ATMOSPHERE, CLIMATE AND WEATHER

The atmosphere is the vast ocean of air that envelops the earth and makes life possible on our globe. It absorbs the heat and vapors caused by the action of the sun upon the surface of both land and water, and is the medium through which the ever-changing phenomena of climate and weather are produced. The two great forces of nature acting in connection with it are gravitation and heat, or solar radiation; and the results of their ceaseless action may be summed up as follows: (1) Temperature, or heat, which we soon learn to know by our senses, and to measure by the thermometer. (2) Evaporation, which changes the weight of the air by carrying invisible moisture through it. This change of weight is indicated by the barometer. (3) Condensation, producing fog, dew, rain, hail, and snow; all estimated accurately by the rain gauge or pluviometer. (4) Motions, as in the winds, varying from the gentle breeze to the awful cyclone, the force and velocity of which are indicated by the anemometer. (5) Electricity, producing lightning, thunder, magnetic and chemical changes in the atmosphere. (6) Optical Phenomena, such as rainbows, haloes, coronas, mirage, and the auroras.

THE ATMOSPHERE: ITS EXTENT, CHARACTER, USE AND EFFECT

The Earth is enveloped in its own atmosphere, which like a transparent covering surrounds it, and revolves with it. This atmosphere does not extend to more than forty or fifty miles above the earth’s surface, and is higher at the equator than at the poles.

[Large illustration] (278 kB)

WHAT THE ATMOSPHERE
IS COMPOSED OF

The atmosphere is an elastic fluid consisting of a mixture (not a compound) of oxygen and nitrogen, in the proportions of about twenty-one of the first to seventy-nine parts of the last named. It also contains a small quantity of carbonic acid gas, and a yet smaller quantity of ammonia; and water in the form of invisible vapor is always present in it, though the quantity is subject to great variations. All these substances move freely among each other, and are continually changing places: the oxygen being ever ready to perform the office assigned to it of sustaining life and combustion; the carbonic acid to promote the growth of vegetation; the nitrogen to perfect the fruits of the earth, and the vapor to descend to the thirsty ground, in the form of showers and dew.

The atmosphere is elastic, and therefore capable of expansion and compression; and is also a ponderable body. The consequence of these properties is, that it is much lighter and thinner in the upper regions than nearer the earth’s surface; for at the sea-level its whole weight presses on its lower strata and gives it greater density. Ascending from the earth’s surface it becomes gradually lighter and thinner, and at great elevations is so rarefied as to be unsusceptible of sustaining life.

HOW THE ATMOSPHERE IS
WEIGHED AND MEASURED

The weight of the atmosphere at the level of the sea is equal to about fourteen and one-half pounds on every square inch of surface. This weight is balanced by a column of mercury thirty inches in height; but at an elevation of 18,000 feet it would be balanced by a column of only fifteen inches in height, and at 36,000 by one only seven and one-half inches in height. It is on this principle that the mercurial barometer has been constructed; and since the mercury in the barometer stands at the same point at all places at the sea-level, and falls in a regular ratio on ascending therefrom, this instrument forms a most useful standard for measuring altitudes.

As we ascend from the sea the atmosphere becomes colder; but, as with the density, the temperature does not appear to pass through regular gradations of change. From experiment, however, it has been assumed that the atmosphere loses one degree of heat by Fahrenheit’s thermometer for every 350 feet of ascent; and hence even in the hotter regions very lofty mountains are covered with perpetual ice and snow.

DISTRIBUTION OF TEMPERATURE
OVER THE EARTH

The amount of heat produced by the sun upon the Earth’s surface, is greatest near the Equator, and diminishes gradually towards the Poles. Three general causes, each referable to the spherical form of the Earth, combine to produce the gradual diminution of temperature from the Equator to the Poles.

1. The angle at which the Sun’s rays strike the surface. In the Equatorial regions they are perpendicular to the surface of the sphere, and there produce their maximum effect; but, on account of the curved outline of the globe, they fall more and more obliquely with increasing latitude, and the intensity of action diminishes proportionately. At the Poles their effect is practically nothing.

2. The area on which a given amount of heating power is expended, is least at the Equator, consequently the resulting heat is greatest. The area covered increases, and the effect diminishes, with the increasing obliquity of the Sun’s rays in higher latitudes, which, as we have seen above, results from the spherical form of the Earth.

3. The absorption of heat by the atmosphere, as the Sun’s rays pass through it, is least where they fall perpendicularly,—that is, in the Equatorial regions,—and increases, with their increasing obliquity, towards the Poles.

EFFECT OF THE MOTIONS
OF THE EARTH

The Earth revolves constantly around the Sun, and at the same time rotates upon an axis inclined twenty-three and one-half degrees towards the plane of its orbit. In consequence of the inclination of the axis, the declination of the Sun, or its angular distance from the Equator, varies with the advance of the Earth in its orbit, causing periodical variations in the length of day and night, and, consequently, in temperature.

Vernal Equinox. On the twentieth of March, at mid-day, the Sun is vertical at the Equator. Rising directly in the east it ascends the heavens to the zenith, and, descending, sets directly in the west.

The illuminated hemisphere extends from pole to pole, and embraces half of every parallel of latitude; hence every point on the Earth’s surface is under the rays of the Sun during half of the diurnal rotation; the days and nights are equal all over the globe; and the heating power of the Sun is the same in both the northern and the southern hemisphere.

Summer Solstice. As the Earth advances in its orbit the vertical Sun declines northward; and on the twenty-first of June, at the Summer Solstice, it is over the northern Tropic, twenty-three and one-half degrees from the Equator.

The illuminated hemisphere, extending ninety degrees on each side of the parallel of the vertical Sun, reaches twenty-three and one-half degrees beyond the North Pole; but, at the south, it barely touches the Antarctic circle. It embraces more than half of each parallel north of the Equator, hence throughout the northern hemisphere the day is longer than the night, the difference in their duration increasing with the latitude; and all points within the Arctic circle are in the light during the entire rotation.

In the southern hemisphere, less than half of each parallel being illuminated, the night is longer than the day, and within the Antarctic circle there is constant night. The heating power of the Sun is now at the maximum in the northern hemisphere, while in the southern it is at the minimum.

Autumnal Equinox. On the twenty-second of September, the distribution of light and heat upon the two hemispheres is the same as at the Vernal, and at the Winter Solstice, on the twenty-second of December, it is the reverse of that at the Summer Solstice.

WHAT CAUSES THE SEASONS AND DAY AND NIGHT

FIGURE ILLUSTRATING THE CHANGE OF SEASONS THROUGHOUT THE YEAR

The change of seasons is caused by the revolution of the earth around the sun, and the inclinations of the planes of the equator and ecliptic. These causes also account for the difference in the length of the days and nights and the difference in the height of the midday sun. The exact duration of the seasons we get by observing the dates of equinoxes and solstices.

FIGURE SHOWING THE CAUSE OF DAY AND NIGHT

The revolution of the earth gives us the length of the year; its rotation on its axis, the length of the day and night, by causing the risings and settings and daily apparent motion of the sun and stars.

EFFECT OF UNEQUAL DAYS AND
NIGHTS ON TEMPERATURE

The inequality in the length of the days in different parts of the year, occasioned by the inclination of the Earth’s axis, is of itself sufficient to produce a marked variation in temperature.

During the day the Earth receives from the Sun more heat than it radiates into space; while during the night it radiates more than it receives. Hence a succession of long days and short nights results in an accumulation of heat, raising the average temperature and producing summer; while long nights and short days result in a temperature below the average, producing winter.

Again, the heating power of the Sun in each hemisphere is greatest at the period of the longest days, because of its greater altitude in the heavens; and least at the period of shortest days. Thus long days and a high sun operate together to produce the high temperature of summer; while long nights and a low sun cause the low temperature of winter.

The following table gives the length of the longest day, excluding the time of twilight, and of the shortest night, in the different latitudes, with the difference of duration in hours and minutes, thus exhibiting more clearly the above law.

TABLE OF UNEQUAL DAYS AND NIGHTS

LATITUDE	Longest Day			Shortest Night			Difference
Equator	12	.0	hours	12	.0	hours	00	.0	hours
10°	12	.7	„	11	.3	„	1	.4	„
20°	13	.3	„	10	.7	„	2	.6	„
Tropics	13	.5	„	10	.5	„	3	.0	„
30°	14	.0	„	10	.0	„	4	.0	„
35°	14	.5	„	9	.5	„	5	.0	„
40°	15	.0	„	9	.0	„	6	.0	„
45°	15	.6	„	8	.4	„	7	.2	„
50°	16	.3	„	7	.7	„	8	.6	„
55°	17	.3	„	6	.7	„	10	.6	„
60°	18	.7	„	5	.3	„	13	.4	„
Polar Circles	24	.0	„	0	.0	„	24	.0	„
67¹⁄₂°	1	month		0	.0	„	...
69¹⁄₂°	2	months		0	.0	„	...
73.3°	3	„		0	.0	„	...
78.3°	4	„		0	.0	„	...
84°	5	„		0	.0	„	...
North Pole	6	„		0	.0	„	...

LAW OF VARIATION OF
DAY AND NIGHT

The inequality of day and night increases slowly in the tropical regions, but more and more rapidly towards the polar circles. Beyond these circles the Sun, in the hemisphere in which it is vertical, makes the entire circuit of the heavens, without sinking below the horizon, for a period varying from twenty-four hours to six months; while in the opposite hemisphere there is a corresponding period of continuous night.

RESULT OF THIS LAW IN
DIFFERENT ZONES

In the tropical regions, where the days and nights vary little in length, the temperature is nearly uniform throughout the year; while the increasing inequality of day and night towards the Poles, causes an increasing difference between the summer and the winter temperature.

Again, the length of the day, in the summer of high latitudes, compensates for the diminished intensity of the Sun’s influence; so that the temperature, in the hottest part of the day, may equal, or even exceed, that within the tropics. A summer day in Labrador or Petrograd may be as warm as one under the Equator; but in the former latitudes there are only a few days of extreme heat in the year, while with increasing nearness to the Equator the number of warm days constantly increases.

HOW THE SEASONS VARY IN
DIFFERENT LATITUDES

The high latitudes have short, hot summers, and long, severe winters. The transition seasons, spring and autumn, on account of the very rapid change in the length of the days, are short and scarcely perceptible.

In the middle latitudes the summer and winter are more nearly equal in length, with less difference in the extreme temperatures; and the transition seasons are distinctly marked. Farther towards the Equator the summer increases in length, and the winter diminishes, while the tropical latitudes have constant summer.

WINDS AND OTHER AIR CURRENTS

The winds appear to be caused by partial changes in the density of the atmosphere in a great measure arising from a diverse distribution of heat. When air is warmed it becomes less dense, or, in other words, it occupies a greater space. If an adjacent stratum of air be cooler, it will on coming in contact with the warmer air expand and pour into space occupied by the latter, thus forming a current. The greater the difference between the temperature of the one or other portion, the greater will be the force which the cold portion will rush into the space occupied by the warm portion, or, in other terms, the more violent will be the wind. In temperate climates the winds are variable; but in some parts of the world they blow with great regularity, and in others are subject to periodical changes.

WHAT CAUSES THE
TRADE-WINDS

The most remarkable of the regular winds are the trade-winds. The atmosphere at the surface between the tropics is much warmer than in the higher latitudes; and since air expands when heated, the light warm air of intertropical regions perpetually rises, and its place is as perpetually supplied by the colder air from the north and the south. If it were not for the Earth’s rotation, these would be merely north and south winds; but like the equinoctial water-currents, these cool currents of air coming from regions which have not an equal velocity of rotation with the air at the equator, pause and hang back, and thus these aerial currents acquire a westerly direction, forming north-easterly constant winds in the northern hemisphere, and south-easterly in the southern hemisphere.

MONSOONS AND THEIR
LOCATION

The monsoons or periodical winds of the Indian Ocean owe their origin to the same cause which gives rise to the trade-winds, though they acquire a different character in consequence of the proximity of the land. In the southern portions of the ocean which are remote from this cause of disturbance, the trade-wind blows with its wonted regularity; but in the seas occupying the region between the eastern coast of Africa on the one side, and the Malay peninsula and the island of Sumatra on the other, the course of the trade-wind is reversed for half the year. This change occurs from April to October; the sun at that period being vertical north of the equator, and the land in the adjacent regions acquiring in consequence a high temperature, and the air over the sea being cooler than that over the land, a south-west wind prevails. This wind, called the “south-west monsoon,” commences at about three degrees south of the equator, and passing over the ocean arrives charged with moisture, and accordingly usually deposits copious supplies of rain in India and some of the adjoining territories. In the remaining half of the year, or from October to April, the wind assumes the ordinary north-easterly direction of the trade-wind.

Sea-breezes, which occur in regions bordering on the ocean in hot climates, are produced by causes similar to those which give rise to the south-west monsoon, but on a more limited scale of action, and changing their direction daily.

THE WHIRL OF THE
HURRICANE

Hurricanes are storms of wind which sweep or whirl round a regular course, and are at the same time carried onward along the surface of the Earth. In the northern hemisphere the whirling motion follows the course of east, north, west, and south to east again, and in the southern hemisphere it takes the opposite course. In the Atlantic Ocean, the principal region of hurricanes lies to the eastward of the West India Islands. They are also frequent in the Indian Ocean, at no great distance from the island of Madagascar. The “typhoons” of the China seas, and the “ox-eye” of the Cape of Good Hope, are also revolving storms.

TORNADOES AND OTHER
CHARACTERISTIC STORMS

The tornadoes of the western coast of Africa, the pamperos of South America, and the northers of North America appear to be of a different character, and not to possess a revolving motion. The sirocco of Italy and Sicily, and the solano of Spain, as also the simoon of Arabia, and the harmattan of western Africa, are all winds which owe their origin to the heated surfaces of Africa and Arabia. The principal difference between these winds appears to be, that the sirocco and the solano acquire some moisture in their passage across the Mediterranean, and therefore do not possess that extreme degree of aridity which forms the distinguishing character of the simoon and the harmattan.

CLOUDS—THEIR FORM AND
CLASSIFICATION

Clouds are continually varying in their form and appearance, but may be classed under the four principal heads of the cirrus, the cumulus, the stratus, and the nimbus.

The cirrus is a light, fleecy cloud resembling a lock of hair or a feather.

The cumulus or summer cloud is generally massive and of a round form; sometimes of small size, and sometimes covering nearly the whole sky, and occasionally appearing in the horizon like mountains capped with snow.

The stratus is a horizontal, misty cloud sometimes observed on fine summer evenings comparatively near the ground, and often crossing the middle regions of mountainous or hilly districts.

The nimbus or rain cloud has a uniform gray tint; it is fringed at the edges when these are displayed, but usually covers the whole sky. The region of clouds is a zone extending in the atmosphere from about one to four miles above the Earth. The most elevated clouds, which are light and fleecy, are those comprehended under the name of cirrus, and the lowest are those which are called stratus.

The cirro-cumulus, cirro-stratus, and cumulo-stratus are only modifications and combinations of the above-named principal classes.

FORMS OF ATMOSPHERIC VAPOR

Warm air is capable of holding suspended a larger quantity of moisture than cold air, and therefore the amount of vapor present in the atmosphere is subject to great variations.

WHAT CAUSES
DEW

These facts also account for the formation of dew, which is caused by the reduction of the temperature and the deposition of the moisture which the warmer atmosphere of the day had held in suspension. Dews will hence be usually most abundant when cool nights succeed warm days, and on a clear night than when the skies are obscured by clouds, because a cloudless sky is usually much colder than a beclouded one. It is also essential for the copious formation of dew, that the ground or other substance on which it is deposited should be much cooler than the superincumbent air; for if the ground be warm it will impart its temperature to the air near its surface and dew will not be formed.

FORMATION OF MISTS
AND FOGS

When the ground or water is warmer than the air, mists and fogs are frequently formed; and since water and marshy surfaces cool less rapidly than dry land, mists and fogs are of more common occurrence in low, damp situations than in dry, elevated districts. They are formed by the condensation of the vapor, or, in other terms, its transformation into the minute globules of water, which instead of descending to the earth in the form of dew, remain suspended above the land or the water.

RAIN, HAIL AND
SNOW

Clouds are formed by the condensation of vapor at considerable but various elevations in the atmosphere. Vapor is always invisible, clouds, therefore, are not vapor but water, and consist of a fine watery powder, the size of each particle being exceedingly minute; and consequently they are so light that clouds formed of an accumulation of such particles are readily borne forward by the winds. Clouds are sometimes suddenly formed and as suddenly disappear, probably owing to sudden and partial changes of temperature. When a considerable difference of temperature prevails in the aerial currents which may come in contact with the local atmosphere, a further condensation takes place, and the particles of this fine watery powder unite into drops, and, becoming heavier, fall to the earth in the form of rain, hail or snow.

SNOW AND SNOW-
CRYSTALS

Vapor condensed in air having a temperature below thirty-two degrees Fahrenheit freezes, or passes to a crystalline form, producing snow. Snowflakes occur in a great variety of forms, which usually present the outline of either a regular hexagon or a six-pointed star.

Their size depends upon the temperature and the relative humidity of the air through which they fall, for, like raindrops, they increase by successive additions from the vapors with which they come in contact in descending. Thus in mild weather they are much larger than in very cold weather.

PICTORIAL CHART OF THE CLOUDS, SHOWING THEIR FORMS AND POSITION

1. Cirrus (sir´rus).—Small curl-like clouds, usually high in the heavens. 2. Cirro-stratus (sir-ro-strā´tus).—Intermediate between the cirrus and stratus. 3. Cirro-cumulus (sir-ro-kū´mu-lŭs).—Resembling the scales of mackerel. 4. Alto-cumulus (al´tō-kū´mu-lus).—High cumulus clouds. 5. Alto-stratus (ăltō-strā´tūs).—High stratus clouds. 6. Strato-cumulus (strā´to-kū´mu-lŭs).—Forms of cumulus and stratus combined. 7. Nimbus (nim´būs).—A rain cloud. 8. Cumulus (kū´mū-lus).—A conical heap of clouds. 9. Cumulo-stratus (kū´mu-lo-stra´tŭs).—Intermediate between the cumulus and the stratus. 10. Stratus (strā´tŭs).—Arranged in a horizontal band or layer. 11. Fracto-stratus (frăk´tō-strā´tŭs).—Broken forms of stratus. 12. Fracto-cumulus (frăk´to-kū´mu-lus).—Broken forms of cumulus.

THE BEAUTIFUL CRYSTAL-FORMS OF SNOWFLAKES

1-3. Six-rayed stars. 4-13, 18-25. Combinations of six-rayed stars with decorated flat surfaces. 14, 16, 17. Combinations of stars and columns. 15. A true pyramid.

When the lower air is warm enough partially to melt the crystals, they form minute balls. When raindrops, formed in the upper air, fall through a cold current, they are often frozen, producing sleet instead of snow.

WHERE PERMANENT
SNOW EXISTS

Though the winter snows upon the plains, and the slopes of mountains of medium height, disappear during the warm season; yet, in all latitudes, the tops of high mountains are covered with a layer of permanent snow, which the summer heat of these great altitudes is not sufficient to melt.

The lower limit of perpetual snow, called the snow line, is found, within the tropics, about three miles above the level of the sea. In temperate latitudes it occurs at the height of a little less than two miles; and at the northern limit of the continents, it is about half a mile above the level of the sea, or, perhaps, even less than this.

On the Arctic Islands, vast fields of snow remain permanently, at a few hundred feet above the sea level.

The winter snows, falling into the icy waters of the polar oceans, are but partially dissolved; and, remaining upon the freezing surface, they help to form those vast ice floes which encumber the polar seas at all times.

The following table gives the observed height of the snow line in the different latitudes:—

HEIGHT OF THE SNOW LINE

Lat. N.	New World	Feet
75°	North Greenland	2,300
54°	Unalaska	3,500
48°	Mt. Baker, Oregon, about	8,000
43°	Rocky Mountains	12,500
39°	Rocky Mountains	14,500
38°	Sierra Nevada	11,000
19°	Popocatepetl, Mexico	14,900
5°	Tolima, Columbia	15,300
Lat. S. 1°	Andes of Ecuador	15,800
17°	Andes of Bolivia, west side	18,500
17°	Andes of Bolivia, east side	15,700
33°	Andes of central Chili	14,700
42°	Andes of Patagonia	6,000
54°	Andes of Straits of Magellan	3,700
75°	Bear Island	600
71°	Mageroe, Cape North	2,300
67°	Sulitelma, Lapland	3,800
61°	Scandinavian Alps	5,300
50°	Altai Mountains	7,000
46°	Alps, north side	8,800
46°	Alps, south side	9,200
43°	Caucasus	11,000
35°	Hindu Kush	13,000
31°	Himalaya, south side	16,200
31°	Himalaya, north side	17,400
12°	Abyssinian Mountains	14,000
Lat. S. 3°	Kilimanjaro	16,000
44°	New Zealand Alps	7,500

HOW SNOW AND ICE FORM
GLACIERS AND ICEBERGS

Glaciers (from the French glace, ice) are vast streams of ice which descend from the lower edge of the perpetual snows, like long icicles from a snow-covered roof. They follow the windings of the Alpine valleys, and terminate abruptly in a massive wall of ice, from beneath which the waters of the melting glacier escape, through a large icy vault.

MOST FAMOUS GLACIER
REGION

The mountain systems in the middle latitudes, with abundant snows and alternate warm and cold seasons, are most favorable to the formation of glaciers. The best known, and probably the most remarkable glaciers are those of the high Alps, in the heart of which are Mont Blanc, Monte Rosa, and the Bernese Alps. Late explorers have found large glaciers in the Caucasus and in the Himalayas, the last being of the grandest proportions. In the Scandinavia are many which descend, in the deep western fiords, nearly to the sea level.

In the New World glaciers are less frequent. On Mount Shasta and Mount Rainier fine examples are in evidence.

By far the most extensive glaciers however, are found on the snow-covered islands of the polar oceans.

Vast masses of ice, broken from the ends of these glaciers, form the enormous icebergs (mountains of ice) which are so numerous in the polar seas, and are transported by the currents even to middle latitudes.

CLIMATE AND WEATHER

The term climate is used to express the combination of temperature and moisture which prevails at any particular place, or, in more familiar terms, the prevailing weather.

The most prominent causes of diversity of climate are the heat of the sun, the respective position of land and water, and the elevation of land above the level of the sea. To these may be added, as producing considerable though less marked effects, the nature of the soil, the prevailing winds, the position of mountain ranges, and the currents of the ocean.

THE SUPREME INFLUENCE
OF THE SUN

The sun is the grand agent in diffusing heat over the earth’s surface. While the sun is above the horizon of any place, that place is receiving heat; and when the sun is below the horizon, it is parting with it by the process called “radiation.” Whenever therefore the sun remains more than twelve hours out of the twenty-four above the horizon of any place, and consequently less than twelve hours below, the general temperature of that place will be above average; and when the reverse occurs, it will be below average. If the temperature depended solely on the heat of the sun, then indeed a tolerably accurate view of the respective climates of the zones of the globe might easily be assumed; but it is so greatly modified by other circumstances, that considerable differences prevail in countries situated in the same parallels of latitude.

HOW AFFECTED BY POSITION OF
LAND AND WATER

The relative position of the land and water is an essential cause of this diversity. The waters of the ocean are of very equal temperature, and have a tendency to moderate both heat and cold, wherever their influence extends. Thus when a cold wind passes over the sea, it becomes warmed, while a hot wind becomes cooled; and thus islands generally experience milder winters and more temperate summers than continents. Such countries are said to possess an insular climate. But when any region experiences great severity of cold in winter and a high degree of heat in summer, it is said to possess an extreme or excessive climate. The most striking instances of an extreme climate are drawn from places like Yakutsk, situated in the depths of Siberia, where the difference between the average temperature of winter and summer amounts to the astonishing sum of 101 degrees Fahrenheit.

THE LIFE-GIVING SUN SENDING HEAT AND LIGHT

The sun is the great life-giver of our earth. Its waves of light and heat and electricity come to the earth through a measureless ocean of ether and make it a living rather than a dead world. The above illustration shows how these waves are constantly bombarding the earth, and not only giving it life but contributing to it the glory of the seasons, the wonders of color, and the brilliant effects of light which we see in the skies and call Auroras, or Northern and Southern Lights.

[Large illustration] (347 kB)

INFLUENCE OF
ELEVATIONS

A gradual decrease in temperature takes place in the ascent from the sea to the line of perpetual snow. This line, which is called the snow-line, varies in different latitudes, and sometimes, owing to local causes, differs on the same latitude; as a general rule, however, a gradual decrease in elevation of the snow-line takes place as we recede from the equator north and south. The height of this line within the tropics varies from 16,000 to 17,000 feet above the level of the sea, and in the northern hemisphere meets the level at about the eightieth parallel.

MODIFICATIONS BY PREVAILING WINDS,
MOUNTAINS AND OCEAN CURRENTS

Countries where the prevailing winds sweep across a wide expanse of ocean are not subject to extremes of heat and cold. Thus the climate of oceanic islands is always moderate, and the climates of all coasts are more equable than in the interior of continents.

Climate is also modified greatly by the position of mountain ranges, especially when ridges extend east and west, screening it from the north or leaving it exposed unsheltered in that direction.

Thus the Carpathians screen Hungary from the cold blasts of the north; while Poland, to the north of that range, and therefore unprotected from those piercing winds, suffers from a very cold and humid atmosphere.

The currents of the ocean are likewise potent agents in the formation of climates, and render places which would otherwise be uninhabitable, fit for man’s habitation. Thus the Polar currents coming to the equatorial regions cool, and the Gulf Stream making its way to Polar regions warms, otherwise extreme temperatures.

RAINLESS AND RAINY REGIONS
OF THE EARTH

In some parts of the Earth extensive tracts exist where rain is never known to fall, and if at all only at intervals, and then in small quantities. The rainless districts of the New World include the flat territories of northern Chili and Peru, some parts of Mexico, and some parts of California. In the Old World an extensive rainless band extends from the western shores of Africa to the central regions of Asia, including the Great Sahara Desert, Egypt, part of Arabia, and the Desert of Gobi. Countries so circumstanced, unless like Egypt rendered fertile by the irrigation of a great river, constitute the most arid and desolate regions of the earth.

The quantity of rain which falls in any region depends greatly on local causes, such as the variations of the surface, the prevailing winds or the proximity of the ocean. Rain is usually more copiously deposited in mountains and well-wooded islands than in any other description of surface.

In tropical regions the rains follow the sun, i. e., when the sun is north of the equator, the rains prevail in the northern tropic, and when south of that line in the southern tropic. This forms the rainy and dry seasons to which countries so situated are subject. This does not, however, apply to the whole intertropical regions, for in a zone extending from the fifth to the tenth parallels on each side of the equator there are two rainy and two dry seasons.

In the narrow belt called the variables, between the regions of the north and south trade-winds, rain is almost incessant, accompanied by thunder and lightning. In many parts of the intertropical regions during the rainy season the rain pours down in such torrents that a larger quantity falls in a few hours than in a whole month in temperate North America.

TRAVELERS GROUPED ON THE SANDS OF THE SAHARA, TERRORIZED BY AN APPROACHING SIMOON

The dreaded Simoon of the desert is a whirlwind of terrific force that raises great gyrating clouds of sand, and sweeps forward with suffocating effect upon both man and beasts. It frequently darkens the sky at midday, and sometimes lightning accompanies it caused by the friction of the sand and air, though no rain falls. The Simoon seldom lasts more than twenty minutes.

NATURE WONDERS OF ELECTRICITY AND LIGHT

Electricity produces an infinity of changes in the natural world. It may be artificially elicited or called forth by friction; or by contact of certain substances and the action attendant on this contact. In the one case it is termed ordinary, and in the other case voltaic or galvanic electricity.

All substances are supposed to contain a certain portion of electricity, and if by friction or other means any substance acquires more electrical action than it would naturally possess, it is said to be positively electrified; and if less, it is said to be negatively electrified. Substances when positively electrified attract or draw toward them other substances which are in a state of negative electricity, or even those which are in a natural state, but will repel or force from them substances which are positively electrified. The sudden contact of bodies in an opposite state of electricity is attended with vivid light called the “electric spark,” and accompanied by explosion and shock.

EARTH AND AIR FORM NATURE’S
ELECTRIC BATTERY

The earth is always in a state of positive electricity, and the air when pure in a state of negative electricity. Atmospheric air, however, is subject to incessant variations, and hence its “electrical equilibrium” or natural electrical state is subject to be disturbed. This equilibrium will be restored when an explosion has taken place, and thus it is that in peculiar states of the atmosphere thunder storms act a beneficial part in restoring the air to a normal condition. The intensity of electrical action is greater during the day than at night and also in summer than in winter; and diminishes from the equator to the poles.

Electricity is perpetually effecting great changes in the earth’s crust, and in very many instances acts on the principal of voltaic electricity, the action in such cases being produced by long-continued currents.

LIGHTNING—THE ELECTRICAL DISCHARGE
IN THE HEAVENS

Lightning is the dazzling light produced by an electrical discharge passing between clouds which are oppositely electrified, or between the clouds and the earth. Lightning flashes have been distinguished as zigzag or chain lightning, sheet and globular lightning.

The first has the aspect of a sharply defined chain of fire, and moves at the rate of 250,000 miles per second. Its zigzag course is attributed to the resistance of the air, condensed in the passage of the electrical discharge, which is sufficient to turn it aside frequently in the direction of less resistance.

Sheet lightning includes the expanded flashes which occur during a storm, and the heat lightning, seen on summer evenings, when no clouds are visible, which is supposed to be the reflection of a storm taking place below the horizon.

Globular lightning is seen on rare occasions, when the electrical discharge takes the form of a ball of fire, and descending with less rapidity, is visible for several seconds. In certain conditions of the atmosphere, globes or spires of electrical light, called St. Elmo’s fire, are seen tipping the extremities of bodies in contact with the earth, like church spires, or masts of ships.

All the conditions which give rise to electrical excitement in the atmosphere are much more intense in warm than in cold latitudes; hence the thunder storms of the tropical regions greatly exceed, both in frequency and in violence, those of temperate and cold climates.

THE AURORA BOREALIS, OR
NORTHERN LIGHTS

This phenomenon is frequently observed in the northern heavens. It occurs in many forms, but the most common is that of a luminous arch whose summit is in the magnetic meridian of the place of observation, and from which vivid flashes of light dart towards the zenith. A like phenomenon in the southern heavens is denominated the Aurora Australis. Auroras are most frequent and brilliant in the polar regions, and diminish in intensity towards the equator.

RAINBOWS, HALOS AND
CORONAS

Rainbows are arches of prismatic colors, formed by the reflection of rays of light from within drops of water. The rays, which are refracted in entering the drops, are reflected from their posterior surfaces, and again refracted as they re-enter the air, the colors being separated by their unequal refrangibility.

Halos and coronas are circles of prismatic colors which, in certain states of the atmosphere, surround the Sun and the Moon.

Halos are supposed to be occasioned by the presence, in the atmosphere, of small ice crystals which act as minute prisms, decomposing and refracting the light which passes through them.

Coronas are seen when a light mist is floating in the air, and are supposed to be formed by reflection from the external surface of the globules of vapor.

COLORS OF THE SKY
AND CLOUDS

The azure tint of the cloudless sky is due to the decomposition and refraction of light, as it passes through layers of air successively increasing in density. The blue and violet, being more refrangible than other colors of the solar spectrum, are diffused through the atmosphere; and being reflected from its particles, they impart to it their own color.

The clouds, floating in the atmosphere, absorb the more refrangible rays, and reflect the less. At sunrise and sunset, when the light traverses the greatest depth of atmosphere, all the colors are absorbed except the red and the yellow; and these, being deflected from the particles of vapor, produce the brilliant coloring of sunrise and sunset.

THE MYSTIFYING
MIRAGE

The mirage is an optical phenomenon in which images of distant objects are seen, reflected beneath, or suspended in the heavens above. Occasionally, also, objects are seen double, being repeated laterally instead of vertically.

The mirage is caused by the refraction and reflection of light as it passes from denser to rarer strata of air. It is most frequent in arid plains, where the soil, exposed to the burning rays of the sun, becomes intensely heated, and, in consequence, the strata of air near the ground are less dense than those above.

In this case rays of light passing from any distant object, as a tree, to the ground, are refracted more and more towards the horizontal, until finally they are reflected from a horizontal layer of the heated air, and reach the eye from beneath. Then an image of the object is seen as if mirrored in the tranquil waters of a lake.

THE MAGNIFICENT CURTAINS OF LIGHT THAT FORM THE AURORA BOREALIS

USEFUL MINERALS OF THE EARTH

HOW MINERALS ARE
IDENTIFIED

Minerals can be identified and distinguished by various physical properties and by ascertaining their chemical composition. The chief distinguishing physical properties are crystalline form, cleavage, hardness, and specific gravity.

Each mineral or special class of minerals has its own definite geometrical shape or crystalline form. The crystals of each mineral have also a tendency to break or cleave most readily in a particular direction. The term hardness, as applied to minerals and other solid bodies, is used to indicate resistance to being scratched or the power to scratch. The harder of two bodies is the one which will scratch the other, and which resists being scratched by that other.

CRYSTALS THE MOST BEAUTIFUL
OF MINERAL FORMS

There are three general classes of crystals—calcareous, silicious and gypsum—but by far the most important are the silicious crystals because of their great hardness. These include quartz or rock crystal—which is quite common—and the so-called precious stones, among which are the diamond, rubies, sapphires, etc., a description of which will be found in the [Dictionary of Minerals].

To find the relative hardness of substances, a scale has been arranged, beginning with the softest mineral (talc) and ending with the hardest (diamond). The minerals of the scale, therefore, are so arranged that each will scratch any other mineral of lower number in the scale, or be scratched by any of higher number.

Scale of Hardness

	Mineral					Chemical Name
1.	Talc.	-	Can be scratched by the finger-nail	-	1.	Magnesium silicate.
2.	Gypsum (or rocksalt).	-	Can be scratched by the finger-nail	-	2.	Calcium sulphate or Sodium chloride.

3.	Calc-spar.	-	Can be scratched by knife or file	-	3.	Calcium carbonate.
4.	Fluor-spar.				4.	Calcium fluoride.
5.	Apatite.				5.	Calcium phosphate.
6.	Felspar.				6.	Potassium and aluminum silicates.

7.	Quartz (rock-crystal).	-	Cannot be scratched by knife or file	-	7.	Silica.
8.	Topaz.				8.	Aluminum fluosilicate.
9.	Corundum (sapphire, ruby).				9.	These gems are crystallized alumina.
10.	Diamond.				10.	Crystallized carbon.

As a first inquiry into the chemical composition of a mineral, dilute hydrochloric or sulphuric acid is tried. All carbonates effervesce when placed in acid or when acid is dropped upon them, while quartz and all the silicates show no effervescense when so treated.

The table on [pages 104-7] contains a brief description of the distinctive physical features of a number of the very common or important minerals.

DICTIONARY OF IMPORTANT MINERAL PRODUCTS

Aluminum, a metal which does not occur in nature in the free state, but for the most part in combination with silica, as a silicate of aluminum, in clay and many minerals. As extracted from clay by a series of very difficult chemical operations, it forms a white metal, very ductile and malleable, and susceptible of a high polish. On account of its lightness, aluminum is highly valued; it forms excellent alloys.

Bauxite (aluminum hydrate) is the only ore. It is mined in France, Ireland, Austria, Arkansas, Alabama and Georgia, and is refined by electric processes. It is used largely as an addition to iron and steel, preventing bubbles and waste in castings; in electrical work, and for purposes where a light, strong metal is necessary, as in certain machinery, hulls for small boats, etc. Refineries are located in Switzerland, France, Great Britain and United States.

Cryolite (fluoride of aluminum and sodium), a mineral mined only in Greenland, was formerly used as an ore but is now utilized in the manufacture of alum and soda.

Alum (a sulphate) is made from cryolite or clays.

Corundum (aluminum oxide) is, next to the diamond, the hardest natural mineral. Canada, North Carolina, Alabama and India have mines of corundum. Emery is produced chiefly in Greece and Asia Minor. Corundum and emery are powdered for use as abrasives in wheels, sharpening stones, polishing powder and cloth.

Emery is an impure form of corundum.

Feldspar is a silicate of aluminum with other metals. It is mined in Canada, Pennsylvania, Connecticut, New York, Maine and Norway, and ground up for use in pottery making.

Clay is chiefly silicate of aluminum and other metals. Kaolin is its purest form. The properties of clay vary with its composition, as china clay, fire clay, pipe clay, brick clay. Clays are found in all parts of the world as a result of the decomposition of other rocks.

The location of manufacturing centers of pottery of all kinds and of bricks, is dependent on clay deposits. In pottery making, Ohio, New Jersey and Pennsylvania lead the United States. Abroad, fine china is made in France, Germany, Austria, England, Japan, and China.

TABLE FOR THE IDENTIFICATION OF COMMON MINERALS; THEIR SCIENTIFIC AND COMMON NAMES AND CHIEF CHARACTERISTICS

Name of Mineral	Common Name	Composition	Hardness	Lustre	Color	Streak	Cleavage or Fracture	Crystallization and Occurrence	Tenacity etc.	Diaphaneity	Varieties	Remarks
Amphibole. (ăm´fĭ-bōl)	...	Silicate of magnesium, calcium, aluminum, iron, etc.	5-6	Glassy to dull.	Black or light to dark green.	White.	Perfect in two directions at angle of 124°.	Prismatic crystals with hexagonal cross-section, common; also cleavable masses.	Brittle to tough.	Opaque to transparent.	Actinolite (green, transparent). Asbestos (fibrous, dull). Hornblende (black).	Common constituent of igneous and metamorphic rocks. Valueless.
Arsenopyrite. (är´sĕn-ō-py̆r´īt)	Mispickel.	Sulphide and arsenide of iron.	6	Metallic.	Silver, yellowish, or light grayish white.	Black.	Good in two directions at an angle of 112°. Not evident on fine grained material.	Crystals resemble a double-edged axe. Occurs also coarse to fine granular.	Brittle.	Opaque.	...	Principal ore of arsenic and sometimes carries gold. Gives sparks and garlic odor when struck with a hammer. Yellow tarnish.
Barite. (bā´rīt)	Barytes. Heavy spur.	Sulphate of barium.	3	Glassy to stony.	White, yellow, blue or brown.	White.	Perfect in one direction; two other good cleavages at right angles to the first and at 101° with each other.	Diamond shaped or rectangular tabular, or prismatic crystals and platy masses.	Brittle.	Transparent to translucent.	...	Used to adulterate white lead and give weight to paper. Often associated with lead ores. Very heavy.
Biotite. (bī´ō-tīt)	Black Mica.	Hydrous silicate of aluminum, potassium, magnesium and iron.	2¹⁄₂-3	Glassy to almost metallic.	Black or dark brown.	White.	Very perfect in one direction, yielding thin sheets.	Six-sided tabular crystals, and as scales, plates, or scaly masses.	Flexible and elastic.	Opaque to transparent.	...	Common constituent of igneous rocks. May be brittle when altered. Valueless.
Calcite. (kăl´sīt)	Lime. Calespar.	Carbonate of Calcium.	3	Glassy to earthy.	Colorless or white when pure, all colors when impure.	White.	Perfect in three directions at angles of about 105° or 75°.	Prismatic or tabular six-sided crystals; also granular, cleavable, or earthy masses.	Brittle.	Transparent to opaque.	Marble (granular). Limestone (dull, compact). Chalk (soft, white, earthy). Mexican Onyx (compact, banded).	Effervesces vigorously in hydrochloric acid of any strength and temperature. Used as flux, building or ornamental stone, to make lime, etc.
Chalcocite. (kăl´kŏ-sīt)	Copper Glance.	Sulphide of copper.	3	Metallic; dull when impure or tarnished.	Dark gray. Tarnishes black or green.	Lead-gray.	No cleavage, smooth conchoidal fracture.	Usually very compact masses; six-sided, tabular crystals rare.	Slightly sectile.	Opaque.	...	An important ore of copper. Cuts easily, yielding a highly polished surface.
Chalcopyrite. (kăl´kō-pĭr´īt)	Copper Pyrites. Fools gold.	Sulphide of copper and iron.	4	Metallic.	Bright brass-yellow. Often tarnished iridescent.	Greenish black.	No cleavage. Uneven fracture.	Occurs massive or in scattered particles. Crystals usually have four triangular faces.	Brittle.	Opaque.	...	One of the most important ores of copper and often carries silver and gold. Is often mistaken for the latter.
Copper.	...	Native metallic copper.	2¹⁄₂-3	Metallic.	Copper-red. Tarnishes green to black.	Copper-red.	No cleavage. Hackly fracture.	Masses, plates, scales, branching aggregates and octahedral crystals, usually distorted.	Malleable sectile.	Opaque.	...	The value and uses of copper are well known. Often carries some silver.
Corundum. (kō-rŭn´dŭm)	...	Oxide of aluminum.	9	Glassy.	All colors; usually gray or brown when massive.	White.	Often parts readily into almost rectangular pieces whose faces are cross-hatched.	Prismatic or tabular six-sided crystals; also granular and pseudo-cleavable masses.	Brittle to tough.	Translucent to transparent.	Ruby (red). Sapphire (blue, etc.). Adamantine. Spar (massive). Emery (granular, impure).	A very valuable gem mineral and a fine abrasive. See plate I, figures 10, 11 and 13.
Epidote. (ēp´ĭ-dōt)	...	Basic silicate of calcium, aluminum and iron.	6-7	Glassy to dull.	Dark green or greenish brown (crystals) to light yellowish green.	White.	Perfect in one direction.	Slender, deeply grooved prismatic crystals and cleavable to fine granular masses.	Brittle.	Transparent to opaque.	...	Common constituent of metamorphic rocks. Rarely cut as a gem.
Fluorite. (flōō´or-īt)	Fluor Spar. Fluorine.	Calcium fluoride.	4	Glassy.	All colors; green, violet, purple, colorless and white, the commoner.	White.	Cleaves easily into octahedrons, i. e., in four directions, at angles of 109° or 71°.	In groups of crystals, usually cubical; also in cleavable masses. Sometimes granular.	Brittle.	Transparent to translucent.	Rock fluorite (finely granular and usually very impure and hard).	Used as a flux in smelting ores, and in several arts and trades.
Galenite. (gȧ-lē´nīt)	Galena. Lead.	Sulphide of lead.	3	Metallic.	Bluish lead, gray. Tarnishes black.	Lead-gray.	Perfect cubical, i. e., in three directions at angle of 90°.	Cubical crystals, often with triangular faces on the corners; also, cleavable to granular masses.	Very Brittle.	Opaque.	Steel galena (very fine grained masses). Often rich in silver.	Most important lead and silver ore. Often contains the latter metal with sometimes gold and other elements.
Garnet.	...	Silicate of various elements: calcium, aluminum and iron are commonest.	6¹⁄₂-7¹⁄₂	Glassy to resinous.	Commonly some shade of red; also brown, yellow, white, black, green.	White.	No cleavage. Uneven fracture.	Complex, rounded crystals, glassy masses and granular.	Brittle.	Transparent to opaque.	...	An important abrasive and a beautiful gem. Found in metamorphic rocks. See plate I, figures 8 and 15.
Gold.	...	Native metallic gold with a little silver, copper, etc.	2¹⁄₂-3	Metallic.	Golden yellow to nearly silver-white.	Yellow to nearly white.	No cleavage. Hackly fracture.	Nuggets, plates, scales, wires; branching aggregates and distorted crystals, usually octahedral.	Malleable sectile.	Opaque.	Based upon and named after any impurities that may be present.	The value and uses of gold are well known.
Graphite. (graph´īt)	Black Lead. Plumbago.	Carbon.	1-2	Metallic to dull.	Dark gray to black.	Dark gray.	Perfect in one direction. Cleavage faces are apt to be curved. Not shown if finely granular.	Imbedded scales and foliated, granular or compact masses. Rarely in six-sided, tabular crystals.	Sectile Flexible.	Opaque.	...	Used in the manufacture of lubricants, infusible crucibles, and “lead” pencils.
Gypsum. (jĭp´sŭm)	...	Hydrous sulphate of calcium.	1¹⁄₂-2	Pearly, silky, vitreous, dull.	White, gray, red, yellow or other tints due to impurities.	White.	Very perfect in one direction; two others show as cracks at angle of 114°, on the perfect cleavage faces.	Diamond shaped crystals, and cleavable, fibrous, granular, foliated or compact masses.	Sectile, Thin flakes, flexible.	Translucent to transparent.	Selenite (cleavable, transparent). Satin spar (white, fibrous, silky). Alabaster, (white, fine grained).	Is carved into vases, statues, etc., and forms plaster of paris when calcined and ground. Is a precipitate rock.
Halite. (hā´līt)	Rock salt.	Chloride of sodium.	2¹⁄₂	Glassy.	Colorless or white when pure. Yellow, brown, red, etc., when impure.	White.	Perfect cubic i. e., in three directions at angle of 90°.	Cubical or octahedral crystals; also cleavable, granular or compact masses.	Brittle.	Translucent to transparent.	...	Tastes salty. Enormous quantities are used to season food, in various arts and trades, and as a source of sodium and its salts. A precipitate rock.
Hematite. (hēm´ȧ-tīt)	Red oxide of iron.	Oxide of iron.	5¹⁄₂-6¹⁄₂	Metallic to earthy.	Black when metallic; reddish black when dull, red when earthy.	Red.	No cleavage; may have a parting in one direction producing a platy structure. Uneven fracture.	Complex, tabular or rounded crystals; also platy, oolitic, earthy, micaceous, and kidney shaped masses.	Brittle.	Opaque.	Specular iron (mirror-like plates or crystals). Red Ochre or Ruddle (red, earthy).	The most important ore of iron, and is also used to make cheap paint, polishing powder, etc.
Limonite. (lī´mŏn-īt)	Yellow oxide of iron.	Hydrous oxide of iron.	5-5¹⁄₂	Dull, silky, varnish-like.	Yellow, brown or nearly black.	Yellow or yellowish brown.	No cleavage. Uneven fracture.	Botryoidal or stalactitic forms with a radiating fibrous structure and a varnish-like surface, also earthy masses and concretions.	Brittle.	Opaque.	Bog iron ore (porous, earthy, often encloses vegetation). Yellow ochre or umber (earthy with clay, etc.).	Commonest, but most impure ore of iron, and is also used to make cheap yellow and brown paint.
Magnetite. (mag´net-īt)	Magnetic iron ore.	Oxide of iron.	5¹⁄₂-6¹⁄₂	Metallic to dull.	Iron-black.	Black.	No cleavage. Sometimes parts in four directions at angles of 109° and 71°. Uneven to subconchoidal fracture.	Octahedral crystals, and coarse to fine granular, laminated, or compact masses.	Brittle.	Opaque.	Lodestone (a natural magnet).	The only black, brittle, magnetic mineral, and a very pure and valuable ore of iron.
Malachite. (măl´ȧ-kīt)	...	Hydrous carbonate of copper.	3¹⁄₂-4	Silky to dull.	Green, often nearly black on exposed surfaces.	Green. Paler than the color.	No cleavage. Uneven fracture.	Massive, as botryoidal crusts with a radiating structure and silky lustre, and as slender crystals forming velvety surfaces.	Brittle.	Translucent to opaque.	...	Is an ore of copper and is used as an ornamental stone and in jewelry. Azur-malachite is malachite mixed with blue azurite. See plate I, figure 4.
Muscovite. (mŭs´ko̱vīt)	Mica, isinglass. White Mica.	Hydrous silicate of potassium and aluminum.	2-2¹⁄₂	Glassy. Pearly on cleavage faces.	White or light tints of other colors, particularly gray, brown or green.	White.	Very perfect in one direction, yielding thin sheets.	Six-sided, tabular crystals, and as scales, plates, or scaly masses.	Flexible and elastic.	Transparent to translucent.	...	Used in stove doors, as insulation in electrical apparatus, and for spangling or frosting paper and fabric.
Orthoclase. (ôr´tho̱-klās)	Feldspar. Potash.	Silicate of potassium and aluminum.	6	Glassy to stony.	Flesh-red, gray, yellow, white or colorless.	White.	In two directions at angle of 90°, one direction slightly less perfect than the other.	Thick-set square or six-sided crystals, or cleavable masses or grains.	Brittle.	Transparent to opaque.	Sanadine (transparent crystals or grains imbedded in igneous rocks).	Associated with quartz and mica in many rocks. Used in making glass and porcelain. Next to quartz in frequency of occurrence.
Pyrite. (pĭr´īt)	Pyrites. White iron. Fools gold.	Sulphide of iron.	6-6¹⁄₂	Metallic.	Pale to deep brass-yellow. Tarnishes brown or iridescent.	Black.	No cleavage. Conchoidal to uneven fracture.	Cubical, octahedral, or complexly rounded crystals, coarse to fine granular, and massive.	Brittle.	Opaque.	...	Used in making sulphuric acid and often contains so much gold, silver and copper as to make it an ore of these metals.
Pyrolusite. (pĭr´o̱-lū´sīt)	...	Oxide of manganese.	1-2¹⁄₂	Metallic to dull.	Black to dark steel-gray.	Sooty black.	May appear to have good cleavage in one direction but usually shows none.	Occurs as radiating prismatic layers, velvety crust and granular to compact masses. Soils the fingers.	Brittle.	Opaque.	...	Has many uses and is valuable. Usually associated with a very fine grained, hard, black mineral that is often botryoidal.
Pyroxene. (pĭr´ŏks-ēn)	...	Silicate of magnesium, calcium, aluminum and iron.	5-6	Glassy to dull.	Black or light to dark green.	White to greenish.	Poor in two directions at angle of nearly 90°. May have a fine platy parting.	Prismatic crystals with square or octagonal cross-section; also foliated and massive.	Brittle.	Transparent to opaque.	Diopside (light green, glassy). Diallage (light green, dull, foliated). Auagite (black).	A common constituent of igneous rocks. Diopside is sometimes used as a gem.
Quartz. (Pheno- crystalline).	...	Oxide of silicon.	7	Glassy.	White or colorless when pure. All colors when impure.	White or light tints.	No cleavage. Single crystal has conchoidal fracture, otherwise the fracture is uneven.	Six-sided prism terminated by a six-sided pyramid; also massive, coarse to fine granular, and as sand.	Brittle.	Transparent.	Rock crystal (colorless, transparent). Amethyst (purple). Rose (pink). False topaz or Citrine (yellow). Smoky quartz or Topaz (brown or gray). Milky (white). Ferruginous (iron stained).	The commonest of all minerals. A constituent of most rock. Great quantities are used as a flux in smelting, as abrasives, and in the manufacture of glass and porcelain. The transparent varieties of pleasing tints are used as gems. Water-clear spheres are very valuable.
Quartz. (Crypto- crystalline).	...	...	...	Dull to earthy.	...	...	No cleavage. Conchoidal fracture.	Very fine grained massive, botryoidal, nodular, or filling or lining cavities in rocks.	Brittle.	Translucent to opaque.	Chalcedony (drab). Carnelian (red, translucent). Jasper (red, brown, yellow, opaque). Heliotrope or Bloodstone (dark green with red spots). Flint (dark gray concretions). Agate (banded or particolored). Onyx (agate with flat layers). Petrified wood (wood replaced by quartz).	...
Serpentine. (sēr´pēn-tīn)	...	Hydrous silicate of magnesium and iron.	4+	Wax-like, silky, earthy.	Light to dark green, yellow, brownish red, variegated.	White.	No cleavage. Conchoidal fracture when massive.	Compact, massive or coarse to fine fibrous. The two habits are often in parallel layers.	Tough. Fibres are flexible.	Translucent to opaque.	Precious or noble (massive, translucent). Chrysolite (silky, fibres). Verde antique (massive with calcite).	Chrysolite is the best commercial asbestos. Other varieties are used as ornamental stone and occasionally in jewelry.
Siderite. (sĭd´ẽr-īt)	...	Carbonate of iron.	3¹⁄₂-4	Glassy to earthy.	Light to dark brown or gray. Tarnishes reddish brown or brownish black.	White to yellowish.	Very perfect in three directions at angle of 107° and 73°. Not evident when fine grained.	Cleavable masses, coarse to fine, granular and at warped crystals that resemble distorted cubes.	Brittle.	Translucent to opaque.	Sphaerosidirite or Clay-ironstone (concretions of fine grained siderite mixed with clay).	The most valuable ore of iron, but is rather uncommon. The impure clay-ironstone is fairly common in sediments.
Sphalerite. (sfāl´ẽr-īt)	Blende, Jack Rosin zinc, zinc, etc.	Sulphide of zinc.	3¹⁄₂-4	Resinous to nearly metallic.	Commonly yellow, brown, black or red; sometimes green or white.	White, yellow or brown.	Very perfect in six directions at angles of 60°, 90° and 120°.	Complexly rounded or modified cubical crystals; also cleavable, coarse to fine granular masses, and botryoidal, etc.	Brittle.	Transparent to opaque.	...	The commonest zinc ore and an impure variety furnishes most of the cadmium of commerce. Associated with galenite and silver minerals.
Stibnite. (stĭb´nīt)	...	Sulphide of antimony.	2	Metallic.	Light gray. Cleavage faces appear silver white when reflecting light.	Lead-gray.	Perfect in one direction, yielding blade-like strips which are bent or hatched perpendicular to their length.	Sharp, vertically grooved, prismatic crystals and in cleavable masses with a bladed structure.	Very brittle.	Opaque.	...	The chief source of antimony and its salts. Sometimes carries gold and silver.
Talc. (tălk)	Talcum.	Hydrous silicate of magnesium.	1-1¹⁄₂	Waxy to dull. Pearly on cleavage faces.	White, light green, gray; other colors when impure.	White to greenish.	Perfect in one direction, yielding thin flexible plates. Not shown on the fine grained soapstone.	Foliated, coarse to fine granular, or compact masses. Feels greasy to soapy.	Tough sectile.	Transparent to translucent.	Steatite or soapstone (granular, impure, hardness up to 2¹⁄₂). French chalk (white, fine grained soft).	Used in making porcelain, polishing powder, lubricants, gas jets, tinted plasters, paper, soap, leather dressing, talcum powder, slate pencils, and in other ways.
Tetrahedrite. (tet´ra-he´drīt)	Gray copper.	Sulph-antimonite of copper.	3-4¹⁄₂	Metallic.	Gray.	Gray, brown, or reddish.	No cleavage. Uneven, granular fracture.	Crystals have four triangular faces. Occurs usually granular massives.	Brittle.	Opaque.	...	Often contains enough silver to make it a valuable ore of this metal as well as copper.
Tourmaline. (tōōr´mȧ-lĭn)	Schorl.	Silicate of boron and various other bases varying with the variety.	7-7¹⁄₂	Glassy to resinous.	All colors. Interior and exterior or opposite ends of a crystal may differ in color.	White.	No cleavage. Uneven to poor conchoidal fracture.	Vertically lined, prismatic crystals with spherical triangular cross-sections. Also columnar or compact massive.	Very brittle.	Transparent to opaque.	Schorl (black). Rubellite (pink). Indicolite (blue). Achroite (white).	A popular semi-precious gem. When heated (not above 212° F.), will usually pick up bits of paper. Opposite ends of crystals have different forms.
Zoisite. (zois´īt)	...	Silica, alumina, lime, peroxide of iron, water.	6	Pearly.	White, gray, yellow, brown.	Uncolored.	Parallel cleavage; sometimes fibrous.	Occurs in tri-metric crystals; also massive.	Brittle.	Transparent, translucent.	...	Often a constituent of metamorphic rocks.

Name of Mineral	Common Name	Composition	Hardness	Lustre	Color	Streak
Amphibole. (ăm´fĭ-bōl)	...	Silicate of magnesium, calcium, aluminum, iron, etc.	5-6	Glassy to dull.	Black or light to dark green.	White
Arsenopyrite. (är´sĕn-ō-py̆r´īt)	Mispickel.	Sulphide and arsenide of iron.	6	Metallic.	Silver, yellowish, or light grayish white.	Black.
Barite. (bā´rīt)	Barytes. Heavy spur.	Sulphate of barium.	3	Glassy to stony.	White, yellow, blue or brown.	White.
Biotite. (bī´ō-tīt)	Black Mica.	Hydrous silicate of aluminum, potassium, magnesium and iron.	2¹⁄₂-3	Glassy to almost metallic.	Black or dark brown.	White.
Calcite. (kăl´sīt)	Lime. Calespar.	Carbonate of Calcium.	3	Glassy to earthy.	Colorless or white when pure, all colors when impure.	White.
Chalcocite. (kăl´kŏ-sīt)	Copper Glance.	Sulphide of copper.	3	Metallic; dull when impure or tarnished.	Dark gray. Tarnishes black or green.	Lead-gray.
Chalcopyrite. (kăl´kō-pĭr´īt)	Copper Pyrites. Fools gold.	Sulphide of copper and iron.	4	Metallic.	Bright brass-yellow. Often tarnished iridescent.	Greenish black.
Copper.	...	Native metallic copper.	2¹⁄₂-3	Metallic.	Copper-red. Tarnishes green to black.	Copper-red.
Corundum. (kō-rŭn´dŭm)	...	Oxide of aluminum.	9	Glassy.	All colors; usually gray or brown when massive.	White.
Epidote. (ēp´ĭ-dōt)	...	Basic silicate of calcium, aluminum and iron.	6-7	Glassy to dull.	Dark green or greenish brown (crystals) to light yellowish green.	White.
Fluorite. (flōō´or-īt)	Fluor Spar. Fluorine.	Calcium fluoride.	4	Glassy.	All colors; green, violet, purple, colorless and white, the commoner.	White.
Galenite. (gȧ-lē´nīt)	Galena. Lead.	Sulphide of lead.	3	Metallic.	Bluish lead, gray. Tarnishes black.	Lead-gray.
Garnet.	...	Silicate of various elements: calcium, aluminum and iron are commonest.	6¹⁄₂-7¹⁄₂	Glassy to resinous.	Commonly some shade of red; also brown, yellow, white, black, green.	White.
Gold.	...	Native metallic gold with a little silver, copper, etc.	2¹⁄₂-3	Metallic.	Golden yellow to nearly silver-white.	Yellow to nearly white.
Graphite. (graph´īt)	Black Lead. Plumbago.	Carbon.	1-2	Metallic to dull.	Dark gray to black.	Dark gray.
Gypsum. (jĭp´sŭm)	...	Hydrous sulphate of calcium.	1¹⁄₂-2	Pearly, silky, vitreous, dull.	White, gray, red, yellow or other tints due to impurities.	White.
Halite. (hā´līt)	Rock salt.	Chloride of sodium.	2¹⁄₂	Glassy.	Colorless or white when pure. Yellow, brown, red, etc., when impure.	White.
Hematite. (hēm´ȧ-tīt)	Red oxide of iron.	Oxide of iron.	5¹⁄₂-6¹⁄₂	Metallic to earthy.	Black when metallic; reddish black when dull, red when earthy.	Red.
Limonite. (lī´mŏn-īt)	Yellow oxide of iron.	Hydrous oxide of iron	5-5¹⁄₂	Dull, silky, varnish-like.	Yellow, brown or nearly black.	Yellow or yellowish brown.
Magnetite. (mag´net-īt)	Magnetic iron ore.	Oxide of iron.	5¹⁄₂-6¹⁄₂	Metallic to dull.	Iron-black.	Black.
Malachite. (măl´ȧ-kīt)	...	Hydrous carbonate of copper.	3¹⁄₂-4	Silky to dull.	Green, often nearly black on exposed surfaces.	Green. Paler than the color.
Muscovite. (mŭs´ko̱vīt)	Mica, isinglass. White Mica.	Hydrous silicate of potassium and aluminum.	2-2¹⁄₂	Glassy. Pearly on cleavage faces.	White or light tints of other colors, particularly gray, brown or green.	White.
Orthoclase. (ôr´tho̱-klās)	Feldspar. Potash.	Silicate of potassium and aluminum.	6	Glassy to stony.	Flesh-red, gray, yellow, white or colorless.	White.
Pyrite. (pĭr´īt)	Pyrites. White iron. Fools gold.	Sulphide of iron.	6-6¹⁄₂	Metallic.	Pale to deep brass-yellow. Tarnishes brown or iridescent.	Black.
Pyrolusite. (pĭr´o̱-lū´sīt)	...	Oxide of manganese.	1-2¹⁄₂	Metallic to dull.	Black to dark steel-gray.	Sooty black.
Pyroxene. (pĭr´ŏks-ēn)	...	Silicate of magnesium, calcium, aluminum and iron.	5-6	Glassy to dull.	Black or light to dark green.	White to greenish.
Quartz. (Pheno- crystalline).	...	Oxide of silicon.	7	Glassy.	White or colorless when pure. All colors when impure.	White or light tints.
Quartz. (Crypto- crystalline).	...	...	...	Dull to earthy.	...	...
Serpentine. (sēr´pēn-tīn)	...	Hydrous silicate of magnesium and iron.	4+	Wax-like, silky, earthy.	Light to dark green, yellow, brownish red, variegated.	White.
Siderite. (sĭd´ẽr-īt)	...	Carbonate of iron.	3¹⁄₂-4	Glassy to earthy.	Light to dark brown or gray. Tarnishes reddish brown or brownish black.	White to yellowish.
Sphalerite. (sfāl´ẽr-īt)	Blende, Jack Rosin zinc, zinc, etc.	Sulphide of zinc.	3¹⁄₂-4	Resinous to nearly metallic.	Commonly yellow, brown, black or red; sometimes green or white.	White, yellow or brown.
Stibnite. (stĭb´nīt)	...	Sulphide of antimony.	2	Metallic.	Light gray. Cleavage faces appear silver white when reflecting light.	Lead-gray.
Talc. (tălk)	Talcum.	Hydrous silicate of magnesium.	1-1¹⁄₂	Waxy to dull. Pearly on cleavage faces.	White, light green, gray; other colors when impure.	White to greenish.
Tetrahedrite. (tet´ra-he´drīt)	Gray copper.	Sulph-antimonite of copper.	3-4¹⁄₂	Metallic.	Gray.	Gray, brown, or reddish.
Tourmaline. (tōōr´mȧ-lĭn)	Schorl.	Silicate of boron and various other bases varying with the variety.	7-7¹⁄₂	Glassy to resinous.	All colors. Interior and exterior or opposite ends of a crystal may differ in color.	White.
Zoisite. (zois´īt)	...	Silica, alumina, lime, peroxide of iron, water.	6	Pearly.	White, gray, yellow, brown.	Uncolored.

Name of Mineral	Cleavage or Fracture	Crystallization and Occurrence	Tenacity etc.	Diaphaneity	Varieties	Remarks
Amphibole. (ăm´fĭ-bōl)	Perfect in two directions at angle of 124°.	Prismatic crystals with hexagonal cross-section, common; also cleavable masses.	Brittle to tough.	Opaque to transparent.	Actinolite (green, transparent). Asbestos (fibrous, dull). Hornblende (black).	Common constituent of igneous and metamorphic rocks. Valueless.
Arsenopyrite. (är´sĕn-ō-py̆r´īt)	Good in two directions at an angle of 112°. Not evident on fine grained material.	Crystals resemble a double-edged axe. Occurs also coarse to fine granular.	Brittle.	Opaque.	...	Principal ore of arsenic and sometimes carries gold. Gives sparks and garlic odor when struck with a hammer. Yellow tarnish.
Barite. (bā´rīt)	Perfect in one direction; two other good cleavages at right angles to the first and at 101° with each other.	Diamond shaped or rectangular tabular, or prismatic crystals and platy masses.	Brittle.	Transparent to translucent.	...	Used to adulterate white lead and give weight to paper. Often associated with lead ores. Very heavy.
Biotite. (bī´ō-tīt)	Very perfect in one direction, yielding thin sheets.	Six-sided tabular crystals, and as scales, plates, or scaly masses.	Flexible. and elastic.	Opaque to transparent.	...	Common constituent of igneous rocks. May be brittle when altered. Valueless.
Calcite. (kăl´sīt)	Perfect in three directions at angles of about 105° or 75°.	Prismatic or tabular six-sided crystals; also granular, cleavable, or earthy masses.	Brittle.	Transparent to opaque.	Marble (granular). Limestone (dull, compact). Chalk (soft, white, earthy). Mexican Onyx (compact, banded).	Effervesces vigorously in hydrochloric acid of any strength and temperature. Used as flux, building or ornamental stone, to make lime, etc.
Chalcocite. (kăl´kŏ-sīt)	No cleavage, smooth conchoidal fracture.	Usually very compact masses; six-sided, tabular crystals rare.	Slightly sectile.	Opaque.	...	An important ore of copper. Cuts easily, yielding a highly polished surface.
Chalcopyrite. (kăl´kō-pĭr´īt)	No cleavage. Uneven fracture.	Occurs massive or in scattered particles. Crystals usually have four triangular faces.	Brittle.	Opaque.	...	One of the most important ores of copper and often carries silver and gold. Is often mistaken for the latter.
Copper.	No cleavage. Hackly fracture.	Masses, plates, scales, branching aggregates and octahedral crystals, usually distorted.	Malleable sectile.	Opaque.	...	The value and uses of copper are well known. Often carries some silver.
Corundum. (kō-rŭn´dŭm)	Often parts readily into almost rectangular pieces whose faces are cross-hatched.	Prismatic or tabular six-sided crystals; also granular and pseudo-cleavable masses.	Brittle to tough.	Translucent to transparent.	Ruby (red). Sapphire (blue, etc.). Adamantine. Spar (massive). Emery (granular, impure).	A very valuable gem mineral and a fine abrasive. See plate I, figures 10, 11 and 13.
Epidote. (ēp´ĭ-dōt)	Perfect in one direction.	Slender, deeply grooved prismatic crystals and cleavable to fine granular masses.	Brittle.	Transparent to opaque.	...	Common constituent of metamorphic rocks. Rarely cut as a gem.
Fluorite. (flōō´or-īt)	Cleaves easily into octahedrons, i. e., in four directions, at angles of 109° or 71°.	In groups of crystals, usually cubical; also in cleavable masses. Sometimes granular.	Brittle.	Transparent to translucent.	Rock fluorite (finely granular and usually very impure and hard).	Used as a flux in smelting ores, and in several arts and trades.
Galenite. (gȧ-lē´nīt)	Perfect cubical, i. e., in three directions at angle of 90°.	Cubical crystals, often with triangular faces on the corners; also, cleavable to granular masses.	Very Brittle.	Opaque.	Steel with galena (very fine grained masses). Often rich in silver.	Most important lead and silver ore. Often contains the latter metal with sometimes gold and other elements.
Garnet.	No cleavage. Uneven fracture.	Complex, rounded crystals, glassy masses and granular.	Brittle.	Transparent to opaque.	...	An important abrasive and a beautiful gem. Found in metamorphic rocks. See plate I, figures 8 and 15.
Gold.	No cleavage. Hackly fracture.	Nuggets, plates, scales, wires; branching aggregates and distorted crystals, usually octahedral.	Malleable sectile.	Opaque.	Based upon and named after any impurities that may be present.	The value and uses of gold are well known.
Graphite. (graph´īt)	Perfect in one direction. Cleavage faces are apt to be curved. Not shown if finely granular.	Imbedded scales and foliated, granular or compact masses. Rarely in six-sided, tabular crystals.	Sectile Flexible.	Opaque.	...	Used in the manufacture of lubricants, infusible crucibles, and “lead” pencils.
Gypsum. (jĭp´sŭm)	Very perfect in one direction; two others show as cracks at angle of 114°, on the perfect cleavage faces.	Diamond shaped crystals, and cleavable, fibrous, granular, foliated or compact masses.	Sectile, Thin flakes, flexible.	Translucent to transparent.	Selenite (cleavable, transparent). Satin spar (white, fibrous, silky). Alabaster, (white, fine grained).	Is carved into vases, statues, etc., and forms plaster of paris when calcined and ground. Is a precipitate rock.
Halite. (hā´līt)	Perfect cubic i. e., in three directions at angle of 90°.	Cubical or octahedral crystals; also cleavable, granular or compact masses.	Brittle.	Translucent to transparent.	...	Tastes salty. Enormous quantities are used to season food, in various arts and trades, and as a source of sodium and its salts. A precipitate rock.
Hematite. (hēm´ȧ-tīt)	No cleavage; may have a parting in one direction producing a platy structure. Uneven fracture.	Complex, tabular or rounded crystals; also platy, oolitic, earthy, micaceous, and kidney shaped masses.	Brittle.	Opaque.	Specular iron (mirror-like plates or crystals). Red Ochre or Ruddle (red, earthy).	The most important ore of iron, and is also used to make cheap paint, polishing powder, etc.
Limonite. (lī´mŏn-īt)	No cleavage. Uneven fracture.	Botryoidal or stalactitic forms with a radiating fibrous structure and a varnish-like surface, also earthy masses and concretions.	Brittle.	Opaque.	Bog iron ore (porous, earthy, often encloses vegetation). Yellow ochre or umber (earthy with clay, etc.)	Commonest, but most impure ore of iron, and is also used to make cheap yellow and brown paint.
Magnetite. (mag´net-īt)	No cleavage. Sometimes parts in four directions at angles of 109° and 71°. Uneven to subconchoidal fracture.	Octahedral crystals, and coarse to fine granular, laminated, or compact masses.	Brittle.	Opaque.	Lodestone (a natural magnet).	The only black, brittle, magnetic mineral, and a very pure and valuable ore of iron.
Malachite. (măl´ȧ-kīt)	No cleavage. Uneven fracture.	Massive, as botryoidal crusts with a radiating structure and silky lustre, and as slender crystals forming velvety surfaces.	Brittle.	Translucent to opaque.	...	Is an ore of copper and is used as an ornamental stone and in jewelry. Azur-malachite is malachite mixed with blue azurite. See plate I, figure 4.
Muscovite. (mŭs´ko̱vīt)	Very perfect in one direction, yielding thin sheets.	Six-sided, tabular crystals, and as scales, plates, or scaly masses.	Flexible and elastic.	Transparent to translucent.	...	Used in stove doors, as insulation in electrical apparatus, and for spangling or frosting paper and fabric.
Orthoclase. (ôr´tho̱-klās)	In two directions at angle of 90°, one direction slightly less perfect than the other.	Thick-set square or six-sided crystals, or cleavable masses or grains.	Brittle.	Transparent to opaque.	Sanadine (transparent crystals or grains imbedded in igneous rocks).	Associated with quartz and mica in many rocks. Used in making glass and porcelain. Next to quartz in frequency of occurrence.
Pyrite. (pĭr´īt)	No cleavage. Conchoidal to uneven fracture.	Cubical, octahedral, or complexly rounded crystals, coarse to fine granular, and massive.	Brittle.	Opaque.	...	Used in making sulphuric acid and often contains so much gold, silver and copper as to make it an ore of these metals.
Pyrolusite. (pĭr´o̱-lū´sīt)	May appear to have good cleavage in one direction but usually shows none.	Occurs as radiating prismatic layers, velvety crust and granular to compact masses. Soils the fingers.	Brittle.	Opaque.	...	Has many uses and is valuable. Usually associated with a very fine grained, hard, black mineral that is often botryoidal.
Pyroxene. (pĭr´ŏks-ēn)	Poor in two directions at angle of nearly 90°. May have a fine platy parting.	Prismatic crystals with square or octagonal cross-section; also foliated and massive.	Brittle.	Transparent to opaque.	Diopside (light green, glassy). Diallage (light green, dull, foliated). Auagite (black).	A common constituent of igneous rocks. Diopside is sometimes used as a gem.
Quartz. (Pheno- crystalline).	No cleavage. Single crystal has conchoidal fracture, otherwise the fracture is uneven.	Six-sided prism terminated by a six-sided pyramid; also massive, coarse to fine granular, and as sand.	Brittle.	Transparent.	Rock crystal (colorless, transparent). Amethyst (purple). Rose (pink). False topaz or Citrine (yellow). Smoky quartz or Topaz (brown or gray). Milky (white). Ferruginous (iron stained).	The commonest of all minerals. A constituent of most rock. Great quantities are used as a flux in smelting, as abrasives, and in the manufacture of glass and porcelain. The transparent varieties of pleasing tints are used as gems. Water-clear spheres are very valuable.
Quartz. (Crypto- crystalline).	No cleavage. Conchoidal fracture.	Very fine grained massive, botryoidal, nodular, or filling or lining cavities in rocks.	Brittle.	Translucent to opaque.	Chalcedony (drab). Carnelian (red, translucent). Jasper (red, brown, yellow, opaque). Heliotrope or Bloodstone (dark green with red spots). Flint (dark gray concretions). Agate (banded or particolored). Onyx (agate with flat layers). Petrified wood (wood replaced by quartz).	...
Serpentine. (sēr´pēn-tīn)	No cleavage. Conchoidal fracture when massive.	Compact, massive or coarse to fine fibrous. The two habits are often in parallel layers.	Tough. Fibres are flexible.	Translucent to opaque.	Precious or noble (massive, translucent). Chrysolite (silky, fibres). Verde antique (massive with calcite).	Chrysolite is the best commercial asbestos. Other varieties are used as ornamental stone and occasionally in jewelry.
Siderite. (sĭd´ẽr-īt)	Very perfect in three directions at angle of 107° and 73°. Not evident when fine grained.	Cleavable masses, coarse to fine, granular and at warped crystals that resemble distorted cubes.	Brittle.	Translucent to opaque.	Sphaerosidirite or Clay-ironstone (concretions of fine grained siderite mixed with clay).	The most valuable ore of iron, but is rather uncommon. The impure clay-ironstone is fairly common in sediments.
Sphalerite. (sfāl´ẽr-īt)	Very perfect in six directions at angles of 60°, 90° and 120°.	Complexly rounded or modified cubical crystals; also cleavable, coarse to fine granular masses, and botryoidal, etc.	Brittle.	Transparent to opaque.	...	The commonest zinc ore and an impure variety furnishes most of the cadmium of commerce. Associated with galenite and silver minerals.
Stibnite. (stĭb´nīt)	Perfect in one direction, yielding blade-like strips which are bent or hatched perpendicular to their length.	Sharp, vertically grooved, prismatic crystals and in cleavable masses with a bladed structure.	Very brittle.	Opaque.	...	The chief source of antimony and its salts. Sometimes carries gold and silver.
Talc. (tălk)	Perfect in one direction, yielding thin flexible plates. Not shown on the fine grained soapstone.	Foliated, coarse to fine granular, or compact masses. Feels greasy to soapy.	Tough sectile.	Transparent to translucent.	Steatite or soapstone (granular, impure, hardness up to 2¹⁄₂). French chalk (white, fine grained soft).	Used in making porcelain, polishing powder, lubricants, gas jets, tinted plasters, paper, soap, leather dressing, talcum powder, slate pencils, and in other ways.
Tetrahedrite. (tet´ra-he´drīt)	No cleavage. Uneven, granular fracture.	Crystals have four triangular faces. Occurs usually granular massives.	Brittle.	Opaque.	...	Often contains enough silver to make it a valuable ore of this metal as well as copper.
Tourmaline. (tōōr´mȧ-lĭn)	No cleavage. Uneven to poor conchoidal fracture.	Vertically lined, prismatic crystals with spherical triangular cross-sections. Also columnar or compact massive.	Very brittle.	Transparent to opaque.	Schorl (black). Rubellite (pink). Indicolite (blue). Achroite (white).	A popular semi-precious gem. When heated (not above 212° F.), will usually pick up bits of paper. Opposite ends of crystals have different forms.
Zoisite. (zois´īt)	Parallel cleavage; sometimes fibrous.	Occurs in tri-metric crystals; also massive.	Brittle.	Transparent, translucent.	...	Often a constituent of metamorphic rocks.

Antimony and Bismuth. Antimony is produced in Germany, France, Italy, Hungary, United States, Japan and other countries.

Bismuth comes mainly from Bolivia and Australia. Some is produced in Saxony and England.

Stibnite (antimony sulphide) is the chief ore of antimony. Bismuth occurs in small amounts in a pure state and also combined with sulphur.

These metals form many alloys such as type metal, anti-friction metals, white metal, babbitt metal, fusible metals.

Tartar emetic and other antimony compounds are used in medicine and dyeing.

Amber is a fossil resin found chiefly along the shores of the Baltic. It is used in making mouthpieces for pipes, cigar holders, beads and other articles.

Arsenic. Germany, England, Canada, the United States and Spain produce the ores. Chemical laboratories transform them into the useful compounds.

Arsenopyrite (arsenic and iron sulphide), orpiment and realgar (sulphides of arsenic) and the sources of arsenic.

Arsenic (white arsenic, arsenious acid or oxide of arsenic), paris green and other compounds and salts are prepared.

Sheep dip, rat poison, insecticides, embalming fluid, pigments and dyes are prepared with arsenic compounds. Arsenic salts are used in preparing certain coal-tar colors.

Asphaltum (or mineral pitch) is a bituminous mineral substance found more or less pure, in some localities. The pitch lake of Trinidad and the Bermudez lake at the mouth of the Orinoco in Venezuela, are the largest known deposits of moderately pure asphalt. Smaller deposits of high grade occur in Utah, Cuba and the Barbadoes.

Rock asphalt consists of sandstone or limestone impregnated with asphalt. Much asphalt is produced in refining certain grades of petroleum—such as those obtained in California and Texas.

Rock asphalts are mined in France, Switzerland, Sicily, California, Kentucky and Oklahoma.

For paving rock asphalts are much used in Europe. Trinidad and Venezuelan asphalts are exported in large quantities to the United States and Europe. For paving, these lake asphalts are mixed with broken stone, sand and petroleum residuum.

Pure varieties (gilsonite, marjak, glance pitch) are made into black varnish, used for insulating, etc.

Barium is mined in the United States and Germany.

Barytes or barite is a heavy, white mineral (barium sulphate). It is used as a substitute or adulterant for white lead in paints, and in making oxygen.

Bismuth. See [antimony].

Building Stones are quarried for local use in all parts of the world.

Granite, syenite, gneiss, basalt and other hard or durable rocks.

Only stone of exceptional beauty is shipped to a great distance. Scotland, Norway, Massachusetts, Maine and other localities produce fine stones.

Calcium has no commercial use in the metallic state. Its compounds, both natural and artificial, are of great economic importance.

Limestone (calcium carbonate) is a very common rock used for building. It may be of almost any color and coarse or fine in texture. It is found and utilized in all parts of the world. In the United States, Pennsylvania, Illinois, Ohio, Indiana, New York and Missouri are the chief producers.

Lime is used in chemical industries and mortar.

Marble is a name applied to limestones suitable for polishing or ornamental work. Mexican onyx is translucent. Fine marbles are quarried in Italy, Egypt, France, Spain and Greece. Vermont, Georgia, Tennessee and New York supply the greater part of the marble used in the United States. Handsome marbles are imported from Carrara, Italy, and other parts of Europe. Mexican onyx is also imported.

Chalk comes mainly from the south of England. We export some Portland cement and import a little from Europe.

Chalk is of peculiar soft texture; whiting is prepared chalk used to make putty and paints; precipitated chalk is similar.

Lime is made by burning (calcining) common limestones. Portland and hydraulic cements are prepared by calcining siliceous limestones or a mixture of limestone and clay. They are of enormous commercial importance, being used in concrete construction work. Europe and the United States produce large quantities. Pennsylvania is the leading state in this industry.

Buildings (both commercial and residences) are now being extensively constructed of cement—in the former case being re-enforced by iron rods.

Chloride of lime (or bleaching powder), acetate of lime, calcium carbide and many other compounds are of industrial value.

Gypsum (hydrous calcium sulphate) is used in fertilizers. Plaster is prepared by calcining (burning) gypsum. Plaster of paris is its purest form. Alabaster is compact white gypsum. It is a common mineral mined in many parts of the world. Michigan, Kansas, New York, Ohio and other states produce it. Fertilizers and plaster use up large quantities of this mineral. Plaster of paris is used for casts, decorative plaster work, cement, etc.

Fluorite (calcium fluoride) is a less common mineral. Mined in England, Kentucky and Illinois. It is used in chemical manufacture and as a flux for ores.

Phosphate rock (chiefly calcium phosphate) is important in the preparation of fertilizers, and chemicals containing phosphorus. It is found in deposits of organic origin in South Carolina, Florida, Tennessee, the West Indies, Canada, Spain, France, Germany and England.

The natural phosphates are treated with sulphuric acid as a first step in the manufacture of phosphatic fertilizers. Exported in large amount to Germany, England and other countries.

Carborundum, or carbide of silicon, is harder than any known substance but the diamond. [109] Much is manufactured at Niagara Falls, by electrically heating a mixture of coke, sand and salt. It is used for making polishing powder, in grinding wheels, sharpening stones, abrasive cloth, etc.

Cerium. See [rare metals].

Chrome is mined in Asia Minor, Greece, Canada, New Caledonia and California. Its salts are prepared in chemical laboratories.

Chromite (oxide of chromium and iron) is the only ore.

Bichromate of potash is the most important compound. It, together with chromic acid, is used in tanning soft leather. A small percentage added to steel makes it very hard and suitable for burglar-proof safes, tools, etc. Salts of chrome are used for dyes and pigments, such as chrome yellow, chrome green, etc.

Coal is one of the most important of all rocks and first among fuels. It consists chiefly of carbon, and is universally regarded as of vegetable origin.

Several theories as to the origin of coal have been put forth from time to time. The one now generally accepted is that the rank and luxuriant vegetation which prevailed during the carboniferous age grew and decayed upon land but slightly raised above the sea; that by slow subsidence this thick layer of vegetable matter sank below the water, and became gradually covered with sand, mud, and other mineral sediment; that then, by some slight upheaval or gradual silting up of the sea bottom, a land surface was once more formed, and covered with a dense mass of plants, which in course of time decayed, sank, and became overlaid with silt and sand as before. At length, thick masses of stratified matter would accumulate, producing great pressure, and this, acting along with chemical changes, would gradually mineralize the vegetable layers into coal.

In passing from wood or peat to coal, the proportion of carbon increases, while that of oxygen and hydrogen decreases, these substances being given off in the form of marsh-gas and carbonic acid gas in the process of decay.

Deposits occur in almost all parts of the world, but many are almost entirely undeveloped; as, for example, the coal fields of China. The largest production is in the United States, Wales, England, Germany, Austria, Russia and Australia. Mines are worked in India, Japan, Mexico, South America, South Africa, China and the Philippines. Pennsylvania, Ohio, West Virginia, Alabama, Indiana, Iowa and many other states mine coal in great amount. Pennsylvania produces nearly all of the anthracite and a large quantity of bituminous coal.

Bituminous coal, coking coal, non-coking coal, cannel coal, cherry coal, splint coal, gas coal, steam coal, etc., are all varieties of soft coal and contain a considerable percentage of volatile matter.

Bituminous coal is the fuel which runs the factories, railways and steamships of the world. The distillation of coal tar and the utilization of its numerous by-products, is one of the best examples of modern economy which turns waste material into useful products and large profits. Much coke is made without saving the by-products.

By distillation, bituminous coal yields gas, ammonia, coal tar and coke. Coal tar products are numbered by the thousand. Among them are naphtha, benzine, oil of mirbane, perfumes, flavors, drugs, saccharine, aniline and other dyes, phenol, carbolic acid, salicylic acid, naphthaline, photographic developers, creosote, oils, tar and pitch.

Anthracite coal is almost pure carbon.

Cobalt is a metal the ores of which are sparingly distributed. It generally occurs as Speiss-cobalt, cobalt-glance (or cobaltite), wad, cobalt-bloom, linnæite and skutterudite. Its minerals are found chiefly in the Erzgebirge Mountains, Sweden, Norway, Chile, in silver ores near Coleman township, Ontario, in Oregon (as garnierite), and in New Caledonia. The metal itself is of a gray color with a reddish tinge, brittle, hard, and very magnetic.

Many of its compounds are valued on account of the brilliance and permanence of their colors. The protoxide of cobalt, is employed in the form of smalt in the production of the blue colors in porcelain, pottery, glass, encaustic tiles, fresco-painting, etc., and forms the principal ingredient in Old Sevres Blue, Thenard’s Blue, etc. The chlorid of cobalt, dissolved in much water, may be employed as a sympathetic ink. In dilute solutions, it is of a faint pink color, which is not observable upon paper; but when heated before the fire, it loses water, and becomes blue, and the writing is then capable of being read.

Copper is, next to iron, the most important metal in use. Its greatest production is in the United States, in Arizona, Montana, Michigan, and Utah. Spain, Japan, Chili, Australia and Germany produce smaller amounts. The metal is purified by smelting, and refined, often by electrolytic methods. There are many ores.

Chalcopyrite and bornite (sulphides of copper and iron) are widely distributed.

Chalcocite (copper sulphide) is mined in Montana, malachite and azurite (carbonates of copper) in Arizona and metallic copper in Michigan.

Copper matte is the crude metal as it comes from the smelter.

Brass and bronze are alloys of copper with zinc, tin, aluminum, etc.

Copper sulphate (blue vitriol) is the most important chemical compound of copper.

The value of copper has increased within recent years, due to its enormous use in electrical work. Aside from this, copper is employed in large amount in the various alloys into which it enters, and in coins, utensils, printing plates, etc. Copper sulphate is extensively used in electrical apparatus dyes, chemical work and as an antiseptic. Large amounts of manufactured copper are exported to Europe. Smaller quantities of ores, matte and regulus are imported from Mexico, South America and other countries. Copper wire is extensively used by telephone and telegraph companies.

Diamond. See [gems].

Gems, or Precious Stones are those which, because of their beauty, hardness, and rarity, are prized for use in ornamentation, especially [110] in jewelry. The diamond, ruby, sapphire, and emerald are the only stones which are, strictly speaking, entitled to be called “precious” in this sense; but the opal, on account of its beauty, is often classed with the precious stones; as is also the pearl, which is really not a stone, but a secretion of a shellfish.

Alexandrite.—A variety of chrysoberyl found in the mica slate of the Ural mountains. It is of a rich garnet color by artificial light, by daylight of a dark moss green. It is the only stone that so changes. The finest specimens of alexandrite are nearly as valuable as diamonds.

Amethyst.—A variety of crystallized quartz of a purple or bluish-violet color, of different shades. It is much used as a jeweler’s stone. The lighter colored ones come from Brazil, the deep purple ones from Siberia. In value they are about the same as the garnet.

Beryl.—A very hard mineral of much beauty when transparent. It occurs in hexagonal prisms, commonly of a green or bluish-green color, but also yellow, pink and white. It is a silicate of aluminum and glucinum. Beryls are very rich in colors.

Bloodstone.—A green siliceous stone sprinkled with red jasper, whence the name.

Cameo.—A figure cut in stone or shell that is composed of different colored layers. The value depends on the artistic merit of the engraved figure.

Carbuncle.—A beautiful gem of a deep red color (with a mixture of scarlet), found in the East Indies. When held up to the sun it loses its deep tinge, and becomes of the color of a burning coal.

Carnelian.—A variety of chalcedony, of a clear, deep red, flesh-red, or reddish-white color. It is moderately hard, capable of a good polish, and often used for seals. It is now used but little.

Cat’s-eye.—A variety of quartz or chalcedony exhibiting opalescent reflections from within, like the eye of a cat. The name is given to other gems affording like effects, especially the chrysoberyl.

Chalcedony.—A translucent variety of quartz, having usually a whitish color, and a luster nearly like wax.

Dendrite.—A stone or mineral in which are branching figures, resembling shrubs or trees, produced by a foreign mineral, usually by an oxide of manganese, and the moss agate.

Diamond.—A precious stone or gem excelling in brilliancy, beauty of prismatic colors, and remarkable for extreme hardness. It is found in many hues—green, rose, straw, yellow, etc.—but the straw-colored ones are the most common. The diamond is a native carbon, occurring in isometric crystals, often octahedrons, with rounded edges. It is the hardest substance known. Diamonds are said to be of the first water when very transparent, and of the second and third water as the transparency decreases.

Diopside.—A crystallized variety of pyroxene (a silicate of lime and magnesia), of a clear, grayish-green color; also called mussite.

Emerald.—A precious stone of a rich green color; it is the most valuable variety of beryl. (See [beryl].)

Epidote.—A mineral, commonly of a yellowish-green color, occurring granular, massive, columnar, and in crystals. It is a silicate of alumina, lime, and oxide of iron, or manganese.

Fluorite.—Calcium fluoride, a mineral of many different colors, white, yellow, purple, red, etc., often very beautiful. When crystallized it is commonly in cubes with perfect octahedral cleavage. Some varieties are used for ornamental vessels. Also called fluor spar, or simply fluor. The colored varieties are often called false ruby, false emerald, false topaz, false sapphire, and false amethyst.

Flint.—A massive, somewhat impure variety of quartz, in color usually of a gray to brown or nearly black. (See [quartz].)

Garnet.—A mineral having many varieties, differing in color and in their constituents, but with the same general chemical formula. The commonest color is red; the luster is vitreous, or glassy; and the hardness is greater than that of quartz, about half as hard as the diamond. Besides the red varieties there are also white, green, yellow, brown and black ones.

The garnet is a silicate with various bases. The transparent red varieties are used as gems. The garnet was the carbuncle of the ancients. Garnet is a very common mineral in gneiss and mica slate.

The finest specimens of red garnets come from Arizona and a single carat stone is worth about two dollars. A green variety that comes from Russia is worth about half as much as the diamond.

Heliotrope or bloodstone.—A green siliceous stone sprinkled with jasper, as if with blood, whence the name.

Hyacinth.—A red variety of zircon, sometimes used as a gem. It resembles closely a dark Spanish topaz, and is worth a little more than the garnet.

Indicolite.—A variety of tourmaline of an indigo-blue color.

Iolite.—A silicate of alumina, iron, and magnesia, having a bright blue color and a vitreous or glassy luster. It is remarkable for its dichroism, and is also called dichroite.

Jacinth.—Same as [hyacinth].

Jade.—A stone commonly of a pale to dark green color, but sometimes whitish. It is hard and very tough, capable of a fine polish, and is used for ornamental purposes and for implements, especially in eastern countries and among many primitive peoples.

Jasper.—An opaque, impure variety of quartz, of red, yellow, and other dull colors, breaking with a smooth surface. (See [quartz].)

Labradorite.—A kind of feldspar, commonly showing a beautiful play of bluish-gray colors, and, hence, much used for ornamental purposes. The finest specimens come from Labrador.

Lapis-lazuli or lazuli.—A mineral of a fine azure-blue color, usually occurring in small rounded masses. It is essentially a silicate of alumina, lime, and soda, with some sodium sulphide. It is often marked by yellow spots or veins of sulphide of iron, and is much valued for ornamental work.

Moonstone.—A nearly pellucid variety of feldspar, showing pearly or opaline reflections from within.

The best specimens come from Ceylon. Their value is not much more than the expense of cutting.

Obsidian.—A kind of glass produced by volcanoes. It is usually of a black color and opaque, except in thin splinters.

Onyx.—Chalcedony in parallel layers of different shades of color. It is used for making cameos, the figure being cut in one layer with the next layer as a background (see [cameo]). It is stained black and used to make mourning jewelry.

Opal.—A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity. The precious opal shows a peculiar play of colors of delicate tints and it is highly esteemed as a gem. One kind, with a varied play of colors in a reddish ground, is called harlequin opal. The fire opal (which comes from Mexico) has colors like the red and yellow of flame. This is not the cheap variety commonly called Mexican opal.

CELEBRATED HISTORIC DIAMONDS OF THE WORLD

Name and Possessor			Carats (Cut)			Carats (Uncut)				Discovered
1.	Great Mogul	Indian Moguls	280			...				17th Cent.
2-11.	Pitt or Regent	King of Prussia	136		⁷⁄₈	410				1702
3-5.	Florentine	Emperor of Austria	139		¹⁄₂	...				...
4-12.	Star of the South	Brazilian Government	127			254				1853
6.	Sancy	Czar of Russia	53		¹⁄₂	83				15th Cent.
7.	Green Diamond[112]	Dresden Museum	40			...				...
8-10.	Koh-i-noor	Crown of England	-	280	(Old)	...				B. C. 56
8-10.	Koh-i-noor	Crown of England	-	106	⁹⁄₁₆ (New)	...				B. C. 56
9.	Hope	Mrs. E. B. McLean, Washington, D. C.	44		¹⁄₂	...				...
OTHER NOTED DIAMONDS

Cullinan I		King Edward VII	-	561	¹⁄₂		-	3,025	³⁄₄	1905
Cullinan II		King Edward VII	-	309	³⁄₄		-	3,025	³⁄₄	1905
Braganza		King of Portugal	Never Cut			1,680				1741
Rajah of Mattan		Rajah of Mattan (Borneo)	367		.9	787			¹⁄₂	1756
Orloff		Czar of Russia (scepter)	194		³⁄₄	...				...
Tavernier		Stolen in 1792	...			242			¹⁄₂	1668
King of Portugal			138		¹⁄₂	150				1775
Light Yellow		Stewart (diamond)	...			288			⁵⁄₈	...
Shah		Czar of Russia	86			...				...
Nassac		Lord (Marquis of) Westminster	78		⁵⁄₈	89			⁵⁄₈	...
Porter Rhodes		Found in South America	...			150				1872
Blue			67		¹⁄₂	112				...
Pigott		Bought by Messrs. Rundell and Bridge	49			...				...
Dudley		Earl of Dudley	49		¹⁄₂	88			¹⁄₂	...
Star of South Africa			46		¹⁄₂	83			¹⁄₂	1867
Pasha of Egypt		Khedive of Egypt	40			...				...
Charles the Bold			28			...				...

Pearl.—A shelly concretion, usually rounded, having a brilliant luster, with varying tints, formed in the mantle, or between the mantle and shell, of certain bivalve mollusks (especially in the pearl oysters and river mussels) and sometimes in certain univalves. Its substance is the same as nacre or mother-of-pearl. Pearls which are round, or nearly round, and of fine luster, are highly prized as jewels. They are sold by carat grains instead of carats.

Rhodonite.—Manganese spar, or silicate of manganese, a mineral occurring crystallized and in rose-red masses. It is almost entirely used for ornamental purposes, in slabs, blocks, etc.

Rock crystal or mountain crystal.—Any transparent crystal of quartz, particularly of limpid or colorless quartz. A sphere of rock crystal of absolutely perfect clearness, about five inches in diameter, is worth at least twenty thousand dollars.

Rose quartz.—A variety of quartz which is pinkish red.

Rubellite.—A variety of tourmaline varying in color from a pale rose-red to a deep ruby, and containing lithium. It is a little more valuable than the garnet.

Ruby.—A precious stone of a carmine-red color, sometimes verging to violet, or intermediate between carmine and hyacinth red. It is a crystallized variety of corundum. The ruby from Siam is of a dark color and is called oxblood ruby. It has about the same value as the diamond. The ruby from Burmah, called the pigeon-blood ruby, is of a lighter color and several times more valuable than the oxblood ruby.

Sapphire.—A variety of native corundum or aluminium sesquioxide. As the name of a gem the term is restricted to the transparent varieties of blue, pink, yellow, and other colors. The best specimens of the blue variety are nearly as valuable as the diamond. The sapphire is next to the diamond in hardness.

Sard.—A variety of carnelian, of a reddish-yellow or brownish color.

Sardonyx.—A variety of onyx consisting of sard and white chalcedony in alternate layers. (See [onyx].)

Spinel.—A mineral occurring in octahedrons of great hardness and various colors, as red, green, blue, brown, and black, the red variety being the gem spinel ruby. It consists essentially of aluminum magnesium, but commonly contains iron and sometimes also chromium. The fine specimens of spinel ruby are worth rather more than half as much as the diamond.

Topaz.—A mineral occurring in rhombic prisms, generally yellowish and pellucid, also colorless, and of greenish, bluish, or brownish shades. It sometimes occurs massive and opaque.

Tourmaline.—A mineral occurring in three-sided prisms. Black tourmaline is the most common variety, but there are also other varieties, as the blue (indicolite), red (rubellite); also green, brown, and white. The red and green varieties, when transparent, are valued as jewels. The finest ones come from Maine, and are worth four or five times as much as garnets.

Turquoise.—A hydrous phosphate of alumina containing a little copper. It has a blue, or bluish-green color, and usually occurs in kidney-shaped masses with a nodular surface like that of a bunch of grapes. The finest specimens are worth nearly half as much as diamonds.

Verd antique.—A mottled-green, serpentine marble, also a green porphyry, which is called oriental verd antique.

Zircon.—A mineral usually of a brown or gray color. It consists of silicon and zirconium, and is harder than the garnet. The transparent varieties are used as gems. The red variety is called Hyacinth; a colorless, pale yellow, or smoky-brown variety from Ceylon is called jargon.

Gold, a metal valued on account of its scarcity, color, luster, and power of resisting oxidation. It is found in nearly all parts of the world. South Africa and the United States are the leading producers. Australia, South America and parts of Europe possess important gold fields.

Gold is separated from gravel (placer mines) by washing with water. The particles of metal, being heavy, sink and can be collected. Rock containing gold is crushed to fine powder and the gold combined with mercury (amalgamation). Low-grade ores are treated with a solution of cyanide of potassium which dissolves the gold and the metal is later separated.

Chloride of gold, used in photographic work, is its only important compound. Pure gold is called twenty-four carats fine. A smaller figure indicates that the metal is alloyed to harden it.

Gold is used for money, jewelry, gold leaf (gilding) and in dentistry. It is almost always alloyed with copper and silver. Gold is the world’s accepted standard of value. Shipments of gold go from one country to another chiefly to balance international business dealings. Government treasuries and bank vaults [113] are the chief storehouses for gold, either as bullion or coin.

Graphite is almost pure carbon. It is produced in Bohemia, Ceylon, Italy, Germany, Mexico and the United States. The deposits in Ceylon are the largest in the world. Much of that mined in New York and Alabama is of very high grade.

Plumbago or black lead is used in making crucibles, lead pencils, lubricants for heavy machinery, stove polish, foundry facings, paint, etc.

Artificial graphite is made from coal or coke by an electric process.

Powdered graphite is mixed with fine clay in greater or less proportion and then molded and baked to form such articles as crucibles and lead for pencils. Graphite is imported from Ceylon to the United States, and lead pencils from Europe.

Iron is the most useful of all metals. The United States, Germany, Great Britain, Spain and France are the greatest producers of iron. Its ores occur in almost all parts of the world. Hematite is mined in Minnesota, Michigan, Alabama and other parts of the United States and in Germany, England, France, Spain, Russia, etc. Limonite is also widely distributed. Pig iron is made by smelting iron ore in a blast furnace. The ore, mixed with limestone, is melted by burning coke, coal or charcoal.

Pyrite (iron pyrites, or fool’s gold) is found in Spain and many other parts of the world and is valuable in the preparation of sulphuric acid (oil of vitriol), but useless as an iron ore.

Hematite (sesquioxide of iron) is the ore which supplies three-fourths of the iron of commerce.

Limonite brown (hematite) is a hydrous oxide and furnishes nearly one-fourth of the world’s supply of the metal. Magnetite and siderite are less common ores.

Pig iron is the crude form of the refined metal and is transformed into cast iron, wrought iron and steel in their multitudinous forms.

These three forms of iron differ in hardness, strength, elasticity, malleability, etc., according to the amounts of carbon, sulphur, phosphorus, manganese and other elements.

Ochers and metallic paints are iron oxides. Prussian blue and copperas are iron compounds.

The United States manufactures more iron and steel than any other country. Almost half of the production is in Pennsylvania. Cast iron appears in many articles but is weaker than other forms of iron. Wrought iron contains less impurity and is used for bars, plates, wire, structural material and parts of machinery. Steel (Bessemer, Siemens-Martin, open hearth, etc.) contains more carbon than wrought iron, possesses both strength and hardness, and is used for rails, structural material, machinery, tools, wire rope, sheet steel, etc. Its hardness may be increased by tempering. The United States imports iron ore from Cuba and Spain, pig iron from Great Britain and a little manufactured iron and steel from Europe. We export large quantities of manufactured iron and steel.

Lanthanum. See [rare metals].

Lead is the softest, heaviest, most malleable and most easily melted of the common metals. Its ores are found in many countries but the main supply is from the United States, Spain, Germany and Mexico. The chief lead mines of the United States are in Missouri, Idaho, Utah, Colorado and Kansas. Much lead bullion is from smelters where silver ores are reduced.

Galena (lead sulphide) is the only important ore; it often carries a considerable percentage of silver. Carbonates and sulphates of lead are less common. Solder and type metal are alloys of lead with tin and antimony. White lead is a carbonate, red lead and litharge are oxides. Chrome yellow and orange mineral are lead compounds used as pigments.

The chief use of metallic lead is in piping, sheet lead, shot and alloys. Large amounts of ore are transformed not into metallic lead but into white lead for use in paints. Lead ores and lead bullion are imported from Mexico. England is the greatest importer of lead and lead ores.

Lithium is the metallic base of the Alkali lithia. The metal is of a white, silvery appearance, and is much harder than sodium or potassium, but softer than lead. It is the lightest of all known solids, its specific gravity being little more than half that of water. It comes principally from South Dakota, California and Sweden.

In chemical laboratories it is converted into lithium carbonate for medicinal tablets and mineral waters.

Magnesium is a metal widely distributed over the globe, and chiefly mined in Austria, Germany and Greece. The metal is used in flash powders for photographic use, and in chemical manufacture, in fireproofing and lining furnaces.

Magnesite (magnesium carbonate) is used in making carbon dioxide gas and epsom salts and for preparing magnesia (calcined magnesia).

Dolomite (magnesium calcium carbonate) is common limestone, used for building. Found in many parts of the world. Calcined dolomite is used for lining iron furnaces.

Talc (hydrous magnesium silicate), soapstone or steatite, is a soft mineral. Mined in Maryland, Virginia, North Carolina, etc., and in Europe. It is made into laundry tubs, firebrick, hearthstones, griddles, slate and tailor’s pencils, gas tips, etc. Imported in small amount from France and Italy.

Meerschaum or sepiolite (magnesium silicate), comes from Asia Minor and New Mexico. It is easily carved and made into pipes and cigar holders. Austria and France use large quantities. It is largely imitated.

Asbestos is a fibrous variety of serpentine (a magnesium silicate). Mineral wool is an artificial fibrous mineral. It is mined in Quebec, Canada. Another variety of asbestos comes from Italy. Mines have been recently discovered in Wyoming. It is used as a fireproofing material. This mineral fiber is spun and woven into fireproof fabrics for theater curtains or made into felt building paper, pipe covering, etc.

Mercury (or quicksilver) is a heavy metal which is liquid at ordinary temperatures. It is produced in Spain, the United States, [114] Austria, Italy and Russia. California supplies most of this country’s quota. It is obtained by distillation of the ore.

Cinnabar (sulphide of mercury) is the source of the metal, although a little is found in nature in the pure state.

Vermilion (artificially prepared cinnabar) is used in paints.

Calomel and corrosive sublimate are used in medicine and fulminates of mercury in explosives.

It is used principally in the extraction of gold and silver from their ores by amalgamation. Employed in thermometers and barometers, silvering mirrors, and in making amalgams for dental work.

Mica is a common mineral found in rocks in many parts of the world. It is mined in India, Canada, North Carolina and South Dakota. Several varieties occur (muscovite, biotite, etc.)—valuable only when found in large sheets which can be split smoothly. Transparent sheets are used for lamp chimneys and stove doors. It is also employed in electrical work, and lubricating. Some is imported from India.

Molybdenum. See [rare metals].

Nickel is found in the ores pyrrhotite and garnierites, mined in largest amount in New Caledonia and Canada. Norway produces other ores.

Garnierite (a silicate of nickel and magnesium) is the common ore. Magnetic iron pyrite (pyrrhotite) often carries several per cent of nickel. Sulphides and other compounds occur. German silver contains nickel, copper and zinc. It enters into other alloys.

France and Germany refine nickel from imported ore, chiefly from New Caledonia. Nickel steel, being especially hard and tough is used for armor plate, special machinery and wire rope. Nickel is extensively used for cheap electro plating.

Nickel and nickel oxide are exported to Holland and England from the United States and ores and matte are imported from Canada.

Petroleum (or coal oil) is obtained from wells in the United States, Russia, Dutch East Indies, Galicia, Roumania and other countries. More than half of the world’s output is from the United States, the leading districts being (1) Kansas and Oklahoma, (2) California, (3) Illinois, (4) Pennsylvania and (5) Texas. Crude oil is transported from the wells for hundreds of miles through pipe lines to the refineries.

In its crude state, petroleum is a dark colored liquid. It yields by distillation, first: light oils, gasoline, naphtha, benzine; second: illuminating oils, kerosene, headlight oil, etc.; third: lubricating oils, engine oil, cylinder oil, machine oil; fourth: petroleum residuum (for asphalt paving) and coke. Petrolatum, vaseline and paraffin wax are by-products in petroleum refining.

American kerosene oil is exported to all parts of the globe. Crude oil is also exported as well as other petroleum products.

Platinum is a rare metal found with gold, iridium and other rare metals in placer mines. It comes chiefly from Russia. Smaller amounts from Colombia, California, Canada and Australia.

It is used in the terminals of incandescent electric lamps, and also employed by chemists, jewelers and dentists.

Potash (or potassium) is an alkaline metal. Chlorides, sulphates, etc., are found in Germany. Wood ashes and sugar beet refuse furnish much of the world’s potash. Stassfurt, Germany, possesses the only known large deposit of natural potash salts. These salts are the source of potash in many chemical industries and in fertilizers. It is exported in large amount from Germany to England, France and America.

Quartz (silica) is of many varieties, crystalline to amorphous.

Rock flint is mined in Connecticut and Pennsylvania, and also comes from the chalk cliffs of England and France.

Sandstones are quarried and used for building in almost all parts of the world. Pennsylvania, Ohio, and New York supply the greatest quantities in the United States. Honestones and whetstones are mostly sandstone, and in this country are largely quarried in Arkansas, Michigan and New Hampshire.

Rock crystal is employed for lenses. Many semiprecious stones are varieties of quartz, as agate, moss agate, onyx, sard, chalcedony, chrysoprase, jasper, etc.

Rock flint and quartz sand are used in making glass and pottery.

Outside of building stones, quartz is used in greatest amount in making glass and pottery. For glass it is melted with alkali (soda ash) and either lime or lead oxide. Glass is either blown or molded. Belgium, Austria, Germany, France, Great Britain and the United States manufacture glassware. Pennsylvania, Indiana and New Jersey are the leading states.

Radium is the most characteristic of those substances which possess the property of radio-activity—i.e. have the power of producing photographic or electric effects by a process identical with or analogous to radiation. The property was first observed in uranium by Becquerel in 1896—hence the name “Becquerel rays.” In 1898 Schmidt and Madame Curie discovered almost simultaneously that the compounds of thorium had the same radio-active property; and further elaborate investigations led to the discovery of polonium, radium, and actinium, as new substances with radio-active properties. Polonium was the name given by M. and Mme. Curie to the radio-active component of bismuth separated from pitchblende. Its activity is transient. In the new field of research thus opened up important work has been done by Rutherford, Crooks, Ramsay, Soddy, Huggins, and others.

Radium is derived from pitchblende, in which it exists in very small quantities. After a long-continued process of fractional crystallization it has been prepared in the form of a tolerably pure salt. The process of obtaining the element is very tedious. One to two kilograms of impure radium bromide can be procured from a ton of pitchblende residue only after processes extending over months. For the remarkable chemical properties of radium, see further under [Radio-activity].

Rare Metals. These include chiefly the following: Tungsten, molybdenum, vanadium and uranium. They are found in Colorado, Arizona, Germany, England and Sweden. The ores of these metals are unusual minerals, and the metals themselves are used in making special high grades of steel. Their salts are used in dyeing.

Thorium, cerium, lanthanum and yttrium, found in North Carolina, Norway, Brazil and Ceylon, are also to be classified under this head. Monazite, samarskite, thorite and other rare minerals contain these elements. They are used in preparing the mantles for incandescent gas lights.

Silver, the more common precious metal, is produced in greatest amount in the Rocky Mountains and the Andes. The United States, Mexico, Australia, Bolivia, Chili, Peru and Germany contribute nearly the entire supply. Montana, Colorado, Nevada and Utah lead in silver production in the United States. The ores are usually smelted and refined to purify the metal.

Argentiferous galena (lead ore) is the commonest ore of silver. The amount of silver per ton varies greatly. Zinc and copper ores often carry silver. Many sulphides of silver (argentite, pyrargyrite, etc.) are found, as well as chlorides and bromides (cerargyrite and bromyrite). Chloride and nitrate of silver are used in photography.

Silver is manufactured into innumerable articles for household use and personal adornment. The cheapest articles are not solid (sterling) but are electrically plated with a very thin coating of silver. Silver coins form the bulk of the currency of the world, although in most countries gold is the standard.

Sodium is the most important alkaline metal, and has a wide use.

Salt (rock salt, sea salt, lake salt, halite or sodium chloride) is the commonest natural compound of sodium. Important for food and in chemical manufacture.

Rock salt is mined in Germany, Austria, Spain, England, Louisiana, Kansas, India and other parts of the world. Obtained by evaporating salt water from wells in England, Michigan, New York, Ohio and China, or by evaporating salt water in the West Indies, Great Salt Lake, etc.

Besides its use for meat packing, curing fish, domestic purposes, etc., it is employed in silver refining, and the preparation of hydrochloric acid, soda ash, carbonate of soda and other chemical products.

Soda niter (nitrate of sodium) is a very easily soluble mineral. It is found in quantity only in the deserts of northern Chili, and is exported in large amounts to Europe and America for fertilizer and the manufacture of nitric acid and other chemicals.

Borax (hydrous sodium borate) occurs in nature in an impure form and is prepared also from calcium borates. Borates are found in Tuscany, Central Asia, California and Nevada, and in South America.

Borax and boracic acid are used in pottery manufacture, for the preservation of meat, in dyeing and in medicine.

Strontium is found in Germany, Scotland, Texas and New York. Strontianite (strontium carbonate) and celestite (strontium sulphate) contain this element. Strontium salts are used in sugar refining and making red fire.

Sulphur or brimstone is found in a pure state in volcanic regions or associated with gypsum and limestone. Pyrite (sulphide of iron) is also a source of sulphur compounds.

Sicily, Italy, Japan, Louisiana and Utah have mines of native sulphur, which is used in manufacturing sulphuric acid, gunpowder, matches, as a disinfectant, for bleaching and vulcanizing rubber.

Blue vitriol, green vitriol and alum are sulphates. Sulphur is imported from Sicily and Italy.

Thorium. See [rare metals].

Tin is less abundant than most of the common metals. The Malay peninsula and nearby islands (Banca and Billiton) produce over half the tin ore of the world. The remainder is mined in Bolivia, Australia, Tasmania and Cornwall, England. Small deposits occur in the United States.

Tin melts at a low temperature and is easily refined.

Cassiterite (tin oxide) is the only important ore. This mineral is commonly found as pebbles (stream tin) in gravel.

Tinplate and alloys containing tin are of enormous importance in the arts. Of these, bronze is chief. Gun metal, pewter, solder, type metal and britannia metal are other alloys. Salts of tin are used in dyeing, glass making, etc.

Tinplate, used for tin cans, roofing and kitchen utensils, is made by dipping sheet iron or steel in a bath of melted tin, thus covering it with a thin layer of tin. Tinplate is manufactured in the United States and imported from England. Tin metal is imported from England and Straits Settlements.

Tungsten. See [rare metals].

Uranium. See [rare metals].

Vanadium. See [rare metals].

Zinc is one of the most useful metals. Germany, United States and Belgium supply most of the zinc. In this country, Missouri and Kansas lead in zinc production.

Sphalerite or blend (zinc sulphide) is the chief ore. Carbonates, silicates and oxides of zinc are found. Crude zinc (spelter) is distilled from roasted ore.

Brass, German silver and other alloys contain zinc. Galvanized iron consists of a coating of zinc on sheet iron. Zinc oxide (zinc white) resembles white lead and is used in paints.

Used in electric batteries, making hydrogen, zinc etchings, etc. The greatest amount of zinc is used in alloys and zinc compounds. Zinc and zinc ores are both imported and exported by the United States, the imports exceeding the exports. Zinc oxide is exported in larger amount than any other form.

HOW AND WHERE WE GET THE SALT FOR OUR FOOD

THE PRODUCTIVE CALIFORNIA SALT BEDS

The United States produces one-fourth of the entire output of the world. Salt was one of the first two great articles of international commerce in the history of the world trade.

AN UNDERGROUND PASSAGE WAY THROUGH SOLID SALT

The most wonderful salt mines in the world are those of Galicia, in Austria. In this region there is a mass of salt estimated to measure 500 miles in length, 20 miles in breadth, and 1,200 feet in thickness.

SCIENTIFIC TERMS USED IN THE EARTH SCIENCES

Acanthodus (a-kan-thō´dus).—Fossil fish, having thorn-like fins.

Aërodynamics (ā-ẽr-ō-di-nam´iks).—The science which treats of the air and other gaseous bodies under the action of force, and of their mechanical effects.

Aërognosy (ā-ẽr-ŏg´nô-sy̆).—The science which treats of the properties of the air, and of the part it plays in nature.

Aërolite (ā´ẽr-ô-līt).—A stone, or metallic mass, which has fallen to the earth from distant space; a meteorite; a meteoric stone.

Aërology (ā-ẽr-ŏl´ôjy̆).—That department of physics which treats of the atmosphere.

Aerometer (ā´ẽr-ŏm´ê-tẽr).—An instrument for ascertaining the weight or density of air and gases.

Ammonites (am´mo-nitz).—Fossil mollusks of spiral form, found in all strata from the palæozoic to the chalk; very numerous, varying greatly in size; all now extinct; sometimes called snakestones.

Anemology (ăn-ĕ-mŏl´ô-jy̆).—The science of the wind.

Anemometer (ăn-ĕ-mŏm´ẽ-tẽr).—An instrument for measuring the force and velocity of the wind; a wind gauge.

Attrition (ăt-trĭsh´ŭn).—The act of rubbing together; friction; the act of wearing by friction, or by rubbing substances together; abrasion.

Aurora (aw-rō´rȧ).—The rising light of the morning; the dawn of day; the redness of the sky just before the sun rises.

Aurora Borealis (bō´rẽ-ā´lĭs), i. e., northern daybreak; popularly called northern lights. A luminous meteoric phenomenon, visible only at night, and supposed to be of electrical origin. This species of light usually appears in streams, ascending toward the zenith from a dusky line or bank, a few degrees above the northern horizon. Occasionally the aurora appears as an arch of light across the heavens from east to west. Sometimes it assumes a wavy appearance. They assume a variety of colors, from a pale red or yellow to a deep red or blood color.

The Aurora Australis (aws-trā´lĭs) is a corresponding phenomenon in the southern hemisphere, the streams of light ascending in the same manner from near the southern horizon.

Barometer (bȧ-rŏm´ẽ-tẽr).—An instrument for determining the weight or pressure of the atmosphere, and hence for judging of the probable changes of weather, or for ascertaining the height of any ascent.

Calamites (kal´a-mīts or kal´a-mī´tēz).—Reed-like plants, found in coal.

Carboniferous (kär´bŏn-ĭf´ẽr-ŭs).—Producing or containing carbon or coal.

Conglomerate (kŏn-glŏm´ẽr-ât).—Pudding stone, composed of gravel and pebbles cemented together.

Corona (kô-rō´nȧ).—A circle, usually colored, seen in peculiar states of the atmosphere around and close to a luminous body as the sun or moon.

Cosmogony (kŏs-mŏg´o-ny̆).—The creation of the world or universe; a theory or account of such creation.

Cosmology (kŏz-mŏl´ô-jy̆).—The science of the world or universe; or a treatise relating to the structure and parts of the system of creation, the elements of bodies, the modifications of material things, the laws of motion, and the order and course of nature.

Crystallography (krĭs´tal-lŏg´rȧ-fy̆).—The science of crystallization, teaching the system of forms among crystals, their structure, and their methods of formation.

Cyclone (sī´klōn).—A violent storm, often of vast extent, characterized by high winds rotating about a calm center of low atmospheric pressure. This center moves onward, often with a velocity of twenty or thirty miles an hour.

Denudation (dĕn´û-dā´shŭn or dē´nū-).—The laying bare of rocks by the washing away of the overlying earth, etc.; or the excavation and removal of them by the action of running water.

Deposit.—A body of ore distinct from a ledge; pocket of gravel or pay dirt.

Diplacanthus (dip-lä-kăn´thus).—A fish, belonging to Acanthodii, known only by fossil remains in Old Red Sandstone.

Drifts.—Tunnels leading off from the main shaft, or from other tunnels or levels, through and along the vein.

Drift Matter.—Earth, pebbles and bowlders that have been drifted by water, and deposited over a country while submerged.

Druse (drṳs).—A cavity in a rock, having its interior surface studded with crystals and sometimes filled with water.

Elephas (el´e-fas).—The Latin name for Elephant. The primitive elephant was what is known as the Mammoth.

Fata Morgana (fä´tȧ môr-gä´nȧ).—A kind of mirage by which distant objects appear inverted, distorted, displaced, or multiplied. It is noticed particularly at the Straits of Messina, between Calabria and Sicily, Italy.

Fire-damp.—An explosive carburetted hydrogen of coal mines.

Fissures.—Seams or crevices in rocks formed by volcanic or earthquake action, and when filled subsequently by metal or metallic ores they become fissure veins.

Fog.—Watery vapor condensed in the lower part of the atmosphere and disturbing its transparency. It differs from cloud only in being near the ground, and from mist in not approaching so nearly to fine rain.

Geography (je-ŏg´rȧ-fy̆).—The science which treats of the world and its inhabitants; a description of the earth, or a portion of the earth, including its structure, features, products, political divisions, and the people by whom it is inhabited.

Astronomical, or Mathematical Geography treats of the earth as a planet, of its shape, its size, its lines of latitude and longitude, its zones and the phenomena due to the earth’s diurnal and annual motions.

Physical Geography or Physiography treats of the conformation of the earth’s surface, of the distribution of land and water, of minerals, plants, animals, etc., and applies the principles of physics to the explanation of the diversities of climate, productions, etc.

Political Geography treats of the different countries into which the earth is divided with regard to political and social institutions and conditions.

Geology (jē-ŏl´o-jy̆).—The science which treats: (a) Of the structure and mineral constitution of the globe; structural geology. (b) Of its history as regards rocks, minerals, rivers, valleys, mountains, climates, life, etc.; historical geology. (c) Of the causes and methods by which its structure, features, changes, and conditions have been produced; dynamical geology.

Goniatites (gō-ni-a-tī´tēz).—Fossil remains of Ammonites, many species of which are found in Devonian and Carboniferous Limestone.

Hail (hāl).—Frozen rain, or particles of ice precipitated from the clouds, where they are formed by the congelation of vapor. The separate particles are called hailstones.

Harmattan (här-măt´tan).—A dry, hot wind, prevailing on the Atlantic coast of Africa, in December, January, and February, blowing from the interior or Sahara. It is usually accompanied by a haze which obscures the sun.

Hoarfrost (hōr´frŏst).—The white particles formed by the congelation of dew; white frost.

Hydrography (hī-drŏg´rȧ-fy̆).—The art of measuring and describing the sea, lakes, rivers, and other waters, with their phenomena.

Hygrometer (hī-grŏm´ê-tẽr).—An instrument for measuring the degree of moisture of the atmosphere.

Ignis fatuus (ĭg´-nĭs făt´ûŭs).—A phosphorescent light that appears, in the night, over marshy grounds, supposed to be occasioned by the decomposition of animal or vegetable substances, or by some inflammable gas,—popularly called also Will-with-the-wisp, or Will-o’-the-wisp, and Jack-with-a-lantern, or Jack-o’-lantern.

Ichthyosaurus (ĭk-thē-ō-saw´rus).—A large marine reptile, known only by fossil vertebræ and other bones, found in oolite rocks.

Labyrinthodon (lab-i-rin´thō-don), or Mastodon. A large animal, belonging to Amphibia, remains of which are found in Upper Trias rocks and strata.

Lepidodendron (lep-i-dō-den´dron).—Coal-plants, belonging to the Lycopods, of which very many remains are found in coal.

Lepidosteus (lep-i-dŏs´te-us).—Bony-pike fish, the fossil remains of which are found in rocks and earth strata.

Lightning (līt´nĭng).—A discharge of atmospheric electricity, accompanied by a vivid flash of light, commonly from one cloud to another, sometimes from a cloud to the earth. The sound produced by the electricity in passing rapidly through the atmosphere constitutes thunder.

Lithology (li-thŏl´ō-jy̆).—The science which treats of rocks, as regards their mineral constitution and classification, and their mode of occurrence in nature.

Lode (lōd).—A metallic vein; a longitudinal fissure or chasm filled with ore-bearing matter and having well-defined side walls; lode, lead, vein and ledge are synonymous; a mineral vein in the rock.

Mastodon (mas´tō-don).—An extinct elephant-like mammal of America, whose teeth have a nipple-like surface.

Metallurgy (mĕt´al-ler-jy̆).—The art of working metals, comprehending the whole process of separating them from other matters in the ore, smelting, refining and parting them; sometimes, in a narrower sense, only the process of extracting metals from their ores.

Meteorology (mĕ-tē-er-ŏl´o-jy̆).—The science which treats of the atmosphere and its phenomena, particularly of its variations of heat and moisture, of its winds, storms, etc.

Min´er-al´o-gy (mĭn-er-ăl´ō-jy).—The science which treats of minerals, and teaches how to describe, distinguish, and classify them.

Mist (mĭst).—Visible watery vapor suspended in the atmosphere, at or near the surface of the earth; fog.

Monsoon (mŏn-sōōn´).—A wind blowing part of the year from one direction, alternating with a wind from the opposite direction—a term applied particularly to periodical winds of the Indian Ocean, which blow from the southwest from the latter part of May to the middle of September, and from the northeast from about the middle of October to the middle of December.

Oceanography (ō´shan-ŏg´rȧ-fy̆).—A description of the ocean.

Oceanology (ō´shan-ŏl´ô-jy̆).—That branch of science which relates to the ocean.

Oreography (ō-rē-ŏg´rȧ-fy̆).—The science of mountains; orography.

Palæotherium (pā-lē-ō-thē´ri-um).—A tapir-like mammal, having canine teeth, known only by fossil remains found in Tertiary rocks.

Pampero (pȧm-pâ´rô).—A violent wind from the west or southwest, which sweeps over the pampas of South America and the adjacent seas, often doing great damage.

Parhelion (pär-hēl´yŭn or hē´lĭ-ŏn).—A mock sun appearing in the form of a bright light, sometimes near the sun, and tinged with colors like the rainbow, and sometimes opposite to the sun. The latter is usually called an anthelion. Often several mock suns appear at the same time.

Petrology (pē-trŏl´ô-jy̆).—The science which is concerned with the mineralogical and chemical composition of rocks, and with their classification; lithology.

Physiography (fiz-e-ŏg´rȧ-fy̆).—The science which treats of the earth’s exterior physical features, climate, life, etc., and of the physical movements or changes on the earth’s surface, as the currents of the atmosphere and ocean, the secular variations in heat, moisture, magnetism, etc.; physical geography.

Plesiosaurus (plē-zi-ō-saw´rus).—An oolithic reptile with crocodile-like head, known by fossil remains, chiefly vertebræ, found in lias and oolitic rocks, named from its fossil remains being found near those of the ichthyosaurus.

Pneumatics (nû-măt´ĭks).—That branch of science which treats of the mechanical properties of air and other elastic fluids, as of their weight, pressure, elasticity, etc.

Pterodactyl (ter-ō-dak´tīl).—Winged lizard: extinct reptile; fossil remains found in Kentish chalk.

Pyroscope (pĭr´ô-skōp).—An instrument for measuring the intensity of heat radiating from a fire, or the cooling influence of bodies. It is a differential thermometer, having one bulb coated with gold or silver leaf.

Rainbow.—A bow or arch exhibiting, in concentric bands, the several colors of the spectrum, and formed in the part of the hemisphere opposite to the sun by the refraction and reflection of the sun’s rays in drops of falling rain. Besides the ordinary bow, called also primary rainbow, which is formed by two refractions and one reflection, there is also another often seen exterior to it, called the secondary rainbow, concentric with the first, and separated from it by a small interval. It is formed by two refractions and two reflections, is much fainter than the primary bow, and has its colors arranged in the reverse order from those of the latter.

Seismology (sīs-mŏl´ô-jy̆).—The science of earthquakes.

Seismometer (sīs-mŏm´e-tẽr).—An instrument for measuring the direction, duration, and force of earthquakes and like concussions.

Simoon (sĭ-mōōn´).—A hot, dry, suffocating, dust-laden wind, that blows occasionally in Arabia, Syria, and the neighboring countries, generated by the extreme heat of the parched deserts or sandy plains.

Sirocco (sĭ-rŏk´kô).—An oppressive, relaxing wind from the Libyan deserts, chiefly experienced in Italy, Malta, and Sicily.

Sivatherium (siv-a-thē´ri-um).—A large four-horned antelope, known by fossil remains found in Pliocene rocks of Hindustan.

Strophomena (strō-fŏm´ĕ-nä).—A genus of shell-like animals similar to the nautilus, found in numerous fossil forms in Lower Silurian and the carboniferous strata.

Tornado (tor-nā´dô).—A violent whirling wind; specifically a tempest distinguished by a rapid whirling and slow progressive motion, usually accompanied with severe thunder, lightning, and torrents of rain, and commonly of short duration and small breadth; a small cyclone.

Typhoon (tï-fōōn´).—A violent whirlwind; specifically, a violent whirlwind occurring in the Chinese seas.

Wind.—Air naturally in motion with any degree of velocity; a current of air.

Zosterites (zos-ter-ī´tez).—Sear-wracks: marine plants, resembling sea-weeds, with small naked flowers, found at the bottom of the sea.