MINERALS.
INTRODUCTION.
1. Minerals are natural bodies destitute of organization and life: and Mineralogy is that branch of natural science which treats of the properties and relations of such bodies.
MINERAL DEPOSITS.
2. If we penetrate beneath the surface of the earth, we observe there a very remarkable arrangement. Instead of a generally uniform appearance, as we see on the surface, we pass through divers substances, as clay, gravel, sand, and numerous others, deposited in beds or strata of various thickness, from a few inches to a great many feet ([Pl. I. Fig. 1]). These lie, for the most part, nearly horizontal: but in some instances, particularly in mountainous countries, they take different degrees of inclination; and, in places where the country consists of gently sloping hills and vales, the beds have a waving or bending form ([Pl. 1, Fig. 3]). The strata of which the earth is composed, as deep as the curiosity or the necessities of mankind have induced them to explore, satisfactorily demonstrate the wisdom which has been displayed in the arrangement of materials requisite for the use of men and animals.
The first layer is frequently a rich, black mould, formed almost wholly of animal and vegetable remains. This yields sustenance to the vegetable productions; and thereby becomes the actual, though not the immediate, support of the whole animal creation.—Beneath this is often found a thick bed of clay, that furnishes to man a substance of which to make bricks, tiles, various kinds of pottery, and innumerable other articles for the comfort of social life.—Next are deposited vast beds of gravel, that are of use in numerous points of view.—Underneath this are the infinitely varying strata of sandstone, limestone, &c. which not only serve for the construction of buildings, and for other important purposes, but also frequently surround mines which contain the valuable metals.—Beneath a slaty stratum are usually discovered those immense beds of coal so requisite for the comfort, and, in some situations, even for the existence of man.
These strata, it is true, are not always found together, nor are they always discovered in the same order; but the statement will suffice to show the general nature of their arrangement.
3. Minerals are sometimes observed in detached masses of various size, and situated at various depths in the earth ([Pl. I, Fig. 1]).
4. They are also found in a kind of natural clefts which cross the regular mineral beds or strata in different directions ([Pl. I, Fig. 1, a], [Pl. I, Fig. 4, b]). When these contain metallic ores, they are styled veins; but when they contain only stony or earthy matters, the miners call them dykes. They vary much both in magnitude and length. Six thousand feet are considered an unusual length for veins, though, in some instances, veins have been traced upwards of four miles. Few veins extend more than 1200 feet below the surface of the mountains in which they are situated. They are usually much inclined; but they sometimes descend in a direction parallel with the beds of rock in which they occur.
5. At the places where dykes or veins pass through the earth, they occasionally disjoint the strata in a very singular manner ([Pl. I, Fig. 4]). Some of the coal strata, for instance, are thrown down or raised on one side of a dyke upwards of a hundred yards; and the miner, after penetrating through this dyke, instead of finding the same coal again, meets, on the opposite side, with beds of stone or clay. Hence he is frequently at a loss how to proceed in searching for the coal of which he is in pursuit; and hence it is that to such dykes the peculiar name of faults has sometimes been given.
6. In England the metallic ores are generally found in veins, that form a considerable angle with the regular strata. This in Cornwall is uniformly the case. And it is remarkable, concerning the veins of tin and copper of that county, that they run in a direction nearly east and west; whilst the dykes, or veins of other substances, run for the most part north and south.
7. The thickness of veins, and the quantity and quality of the ores they contain, differ in every mine. Some are only a few inches wide, whilst others extend to the width of several feet. The vein at Dalcooth mine, in Cornwall, varies from two or three to forty feet and upwards; and, in some parts, it contracts so as to be little more than six inches across.
8. In Cornwall the first traces of tin and copper are usually found at the surface of the ground, and thence to the depth of 80 or 100 feet beneath; and it is said that no miner has ever yet seen the bottom of a vein, although several have been wrought to the depth of more than 1000 feet. The veins of these metals have, in some instances, been worked to the length of three or four miles.
9. It is frequently observed that metallic veins are separated, from the substances they intersect, by a thin wall, or lining, of minerals different from these substances, and also by a layer of clay on each side of the vein. It is also remarked that the same substance which forms the outer coat of the vein is often intermixed with the ore, or forms layers alternately with it. This has usually the denomination of matrix or gangue.
10. There are few mines of any considerable depth that would not be flooded with water from internal springs were not means adopted for drawing off this fluid. The steam engines that are employed for this purpose in some of the Cornish mines are so powerful as to discharge incessantly, both by night and day, a quantity of water, equal to at least 1000 gallons, or near twenty hogsheads, every minute.
SYSTEMATIC ARRANGEMENT OF MINERALS.
11. To a superficial observer, perhaps nothing would appear more easy than to describe a mineral. This, however, is by no means the case. The same general appearance sometimes prevails in substances that are very different from each other; and the same stone, in its different states, is often extremely varied in its appearance. To these difficulties it must be added, that the combinations of mineral substances are multiplied to a great extent. A little application, however, particularly if the student be possessed of a collection of arranged and named specimens, which he will have no difficulty in procuring at a reasonable price, will enable him to overcome all the obstacles that otherwise might impede his progress in beginning to acquire a knowledge of this interesting science.[[1]]
12. The most simple and natural division of minerals is into four classes, of, 1. Stones; 2. Salts; 3. Combustibles; and, 4. Metals; and the following table, which has chiefly been arranged from the system of Werner, the well-known German mineralogist, will exhibit a tolerably correct outline of the classification of these substances. To reduce the whole within the compass of a single page, many of the families, however, have necessarily been omitted.
[1]. Such collections are supplied by Mr. Mawe, No. 149, Strand, London. His terms, for collections containing from 100 to 200 specimens, are 5 guineas; from 200 to 300 specimens, 10 guineas; and from 300 to 400 specimens, 15 guineas. For collections containing from 350 to 400 specimens, more select, and comprising a better suite of precious stones, he charges from 20 to 30 guineas; and for larger collections, from 50 to 100 guineas. At the particular request of the author, Mr. Mawe has arranged a few collections of minerals, and numbered them in such manner as to correspond with, and illustrate the present volume.
13.To complete a general view of the different productions of the mineral kingdom, it is requisite to subjoin a tabular arrangement of the various kinds of rocks.
14. For the purpose of ascertaining the names and characters of minerals, attention must be paid to their form, surface, lustre, fracture, or the appearance of their internal surface when broken; structure, transparence, streak, or the mark left when scratched by any hard body; stain, or trace left when rubbed upon paper; cohesion, whether solid, friable, or fluid: hardness, or the resistance which they oppose when scratched; tenacity, or the resistance which they oppose to the stroke of a hammer; flexibility, or their property of bending without breaking; feel, or the sensation communicated by their surfaces when handled; smell, taste, adherence to the tongue, sound, specific gravity, or weight in comparison with that of water; colour and electricity.
15. To ascertain the chemical properties of minerals, one of the most important instruments is the blow-pipe. This is a tube which terminates in a cavity as fine as a small wire, and through which the air is forced, and made to play upon the flame of a candle. The flame is thus concentrated, and directed against small particles of the mineral to be examined, which is placed upon a bit of charcoal in a spoon of platina or silver. The air is forced into the blow-pipe by the mouth of the person using it, or by bellows attached to it for that purpose. Under this operation we have an opportunity of trying the action of other bodies upon minerals at a very high temperature; and the properties which these experiments bring into view enable us, in many cases, to ascertain, not only the nature, but even the component parts, of minerals.
SIMPLE MINERAL SUBSTANCES.
16. As a necessary introduction to the study of minerals, it is requisite to describe, in a brief manner, such simple substances as form their constituent parts. Few of these, it is true, are to be found in a separate, uncombined state; yet that they do exist, and that they are to be obtained from the minerals with which they are united, we have the proof of every day’s experience.
UNCONFINABLE FLUIDS.
17. There are some kinds of unconfinable fluids, the existence even of which is manifested only by their contact with other bodies, or becoming separated from them. They are of a nature too subtile to be collected or confined in our vessels for the purpose of examination, and the investigation of their properties has consequently been attended with peculiar difficulty. Those at present known are caloric, light, electricity, and magnetism; but of these the first only is immediately connected with the subjects of our present investigation.
18. Caloric.—Every one is acquainted with the different sensations of heat and cold. That matter which produces on our bodies the sensation of heat has the name of Caloric; heat being only an effect, of which caloric is the cause. This is extended in a greater or less degree through the whole extent of space, and penetrates into the interior of even the most solid bodies: in so doing it expands the particles of which they are composed, augments their bulk, and diminishes their solidity. The sun is the principal fountain from which the earth is supplied with this fluid; and it passes thence to us at the rate of 12,000,000 of miles per minute. The defect of caloric in any substance occasions the sensation called cold.
Were the world deprived of caloric, every species of organized being would, from that moment, cease to exist. It is the cause of all fluidity: to it every production of the earth has been most essentially indebted, even for its form and structure; and in no respect do the power and goodness of the Almighty appear more conspicuous than in the creation, dispersion, and continuance, of this most subtile and astonishing fluid.
19. All the various substances with which we are acquainted must be considered either as solid or fluid. Every substance is defined to be a solid in which the parts are so united or connected that it requires an external force to separate them. A fluid, on the contrary, is a body the parts of which are so loosely connected that they not only yield easily to any force impressed upon them, but also move freely amongst each other; and every fluid is a combination of caloric with some other substance.
20. Fluids are of two kinds: one of these, called liquids, have, when at rest, a smooth and distinct surface, and are distinguishable both by the sight and touch; the other, denominated gas, or gaseous fluids, have the appearance of air, and are not perceptible either to the sight or touch, except under certain circumstances. The latter are principally oxygen ([21]), azote or nitrogen, and hydrogen ([45]). We shall at present have occasion to speak only of the first.
GASEOUS FLUIDS.
21. Oxygen, like caloric, is a fluid never found in an uncombined state. It forms one of the component parts of the air that we breathe, and of the water we drink; but it approaches nearest to a state of purity in combination with caloric ([18]), when it has the name of oxygen gas. It was formerly called vital air, because no breathing animal can live for a moment in any air or gas which has not in it a mixture of oxygen; every kind of combustible burns with great splendour in it, and without it ceases to burn. It unites with a great number of substances, and changes both their appearance and properties in a very remarkable manner. Of the metals it entirely destroys the metallic lustre, and gives them an earthy form and texture. Substances in this state have the name of oxides.
Lead, for instance, combined with oxygen becomes the well-known red and heavy substance used by painters, under the name of minium or red lead ([239]). This, if deprived of its oxygen, loses its red colour, and returns to its former metallic state. Some of the metals are oxidized by merely being exposed to moisture. Thus the rust which is so readily contracted by iron is an oxide of that metal, produced by its attracting oxygen from the air or from water.
ACIDS.
22. It is one of the most remarkable properties of oxygen to impart to most of those bodies called acids their peculiar character of acidity. Oxygen does not itself possess the properties of an acid, nor is it an essential ingredient in all acids, though it is the acidifying principle in the greater number of them.
23. Acid is a word originally synonymous with sour. It has, however, been gradually extended in its signification, and now comprehends all substances possessed of the properties of exciting upon the tongue the sensation called sour; of changing the blue colours of vegetables to red; of uniting with water in almost any proportion; of combining with alkalies ([42]), metallic oxides, and earths, and of forming with them certain compounds called salts.
24. Sulphuric Acid, or Spirit of Vitriol, as it is commonly called, is a liquid of a somewhat oily consistence, transparent and colourless as water, formed by a combination of oxygen ([21]) with sulphur ([46]). Like other acids, it never occurs in nature in a pure state, for it can no sooner be formed than it unites with earths ([31]), alkalies ([42]), or metals, and forms, with them, several well-known salts, which have the name of sulphats. Thus alabaster ([192]) and Epsom salts ([199]) are respectively formed by an union of sulphuric acid with lime and magnesia, and are denominated by chemists sulphat of lime and sulphat of magnesia. In like manner, blue vitriol ([209]) is sulphat of copper; green vitriol ([208]), sulphat of iron; and white vitriol ([210]), sulphat of zinc.
25. Phosphoric Acid is produced by a combination of oxygen ([21]) with phosphorus ([47]); and, when obtained in a state of purity, is not a fluid, but a white and flaky substance. This acid, when combined with mineral productions, forms those salts which have the name of phosphats. It is very soluble in water; and, in dissolving, makes a hissing noise, similar to that produced by plunging hot iron into water.
26. Carbonic Acid is a compound of oxygen ([21]) and carbon, or pure charcoal ([48]): and in a state of gas ([20]) it forms a constituent part of the atmospheric air. It is also emitted in great abundance from wine, beer, and other liquors, in a state of fermentation, and is sometimes found in the lowest parts of mines, where it is known to the miners by the name of choke damp, from the circumstance of its immediately extinguishing flame, and suffocating all animals that are immersed in it. This gas, which was formerly called by chemists fixed air, is about twice the weight of common air. In combination with lime it forms chalk, marble, and limestone; and it constitutes part of several other mineral substances, which are thence denominated carbonats.
27. Fluoric Acid is a gas of very singular nature, which is held in combination with lime, in the Derbyshire or fluor spar ([194]); and may be separated from it by pouring sulphuric acid, or spirit of vitriol ([24]), upon powdered spar, in a leaden vessel called a retort, and applying to it a gentle heat. The salts formed by fluoric acid have the name of fluats.
28. The Boracic is a peculiar kind of acid, which, in combination with soda ([200]), forms the substance that we import from the East Indies under the name of borax ([204]). When extracted from borax this acid does not assume the form of a fluid, but appears in thin six-sided scales or flakes, of white colour, which adhere slightly together, and feel somewhat greasy in handling. To the taste it is at first sour, then bitterish; and at last it leaves an agreeable sweetness on the palate.
29. Muriatic Acid is a gas formed by the combination of oxygen ([21]) with some base that is not yet known. It is an invisible and elastic fluid, which, in mechanical properties, resembles common air, and has a pungent and very peculiar smell. This gas unites with alkalies ([42]), earths ([31]), and the oxides ([21]) of metals; and with them forms the compounds called muriats, of which common salt, or muriat of soda ([202]), is one of the principal. The liquid muriatic acid, or muriatic acid gas combined with water, is frequently denominated spirit of salt ([202]).
30. Nitric Acid is a compound of oxygen and azote, or nitrogen, in the proportion of twenty-five parts, by weight, of the latter to seventy-five of the former. It is one of the constituent parts of nitre, or saltpetre ([206]); and, in a pure state, is transparent and colourless, like water. By the action of light, however, it soon becomes yellow; and, if exposed to the air, it emits yellow fumes, which even tinge the air of the same colour. To the taste it is extremely acid. It dyes the skin a yellow colour, which is very difficult to be removed; and it is so corrosive as to destroy almost every substance into which it penetrates. If poured upon oils, it sets them on fire. With various bases it forms compounds called nitrats. This acid, which hitherto has never otherwise been obtained than mixed with water, is chiefly known in commerce by the name of aqua fortis ([206]).
EARTHS.
31. The solid contents of the globe are composed of several elementary substances, amongst which have been enumerated no fewer than nine different kinds of earth:
1. Silex.
2. Alumine.
3. Zircon.
4. Glucine.
5. Yttria.
6. Barytes.
7. Strontian.
8. Lime.
9. Magnesia.
These, when freed from foreign admixture, are, for the most part, of white colour, not soluble in water, not combustible, and do not exceed four times the weight of water.
32. The whole of these earths have, till lately, been considered simple and uncombined substances; but, by the discoveries of Sir Humphrey Davy, it has been ascertained that four of them have a metallic basis, and are in fact metallic oxides, or compounds consisting of a metal united with oxygen ([21]). These, which have the same affinity with their respective bases as rust has to iron, are silex, lime, barytes, and alumine. Until, however, some further light be thrown upon their nature and constitution, they must continue to hold their former situation of simple earths.
33. Silex, or Siliceous Earth, is the basis of all substances known by the name of quartz and silex ([76]). In a state of nature it has never been found pure; but, in combination with other substances, it abounds in almost every country of the globe. Common flint ([90]) contains ninety-seven parts in a hundred of silex: it consequently has given its name to this earth, silex being the Latin word for flint. When purified it is a white powder, the particles of which are harsh to the touch, as if they consisted of very minute grains of sand. It is not quite three times as heavy as water, and has neither taste nor smell. Water will not dissolve it, nor any kind of acid, except fluoric. Sir H. Davy has discovered it to have a metallic basis, to which he has given the name of silicium.
34. Alumine is a kind of earth, so called from its forming the basis of alum ([197]). It is soft, compact, and tenacious; about twice the weight of water, and, when breathed upon, has a smell which is peculiar to all clayey productions. In the fire it shrinks, and becomes so hard as even to yield sparks when struck against steel. It readily absorbs water, and is dissolved by most acids. Some writers state that pure alumine has been discovered in a native state near Halle, in Germany. It is found in a crystallized form, and nearly in a state of purity, in the Oriental ruby and sapphire. The name of argil, or clay, has sometimes been applied to it; but, in mineralogy, this name has usually been given to a mixture of alum, quartz, and other substances. Sir H. Davy has obtained from alumine a metallic basis, called aluminum.
35. Zircon, when freed from those substances with which it is combined, is a white and somewhat rough powder, insipid to the taste, insoluble in water, and about four times as heavy as that fluid. It is found in the two kinds of precious stones called jargoon and hyacinth, and has not hitherto been applied to any useful purpose.
36. Glucine is a kind of earth of peculiar nature, which is found in the emerald and beryl, and, when purified, forms a soft and white powder, without smell, and of sweetish taste. To the last of these qualities it is indebted for its name, which is derived from a Greek word signifying sweet. It is somewhat unctuous to the touch, and about three times as heavy as water. The uses of this earth, whatever they may be, are not known.
37. Yttria is an earth which, among other particulars, differs from glucine by its weight, as it is nearly five times heavier than water. In a natural state it occurs as the basis of a black Swedish mineral, called gadolinite. When cleansed, by chemical process, from all its impurities, it is a fine, white, and inodorous powder.
38. Barytes is a white, porous, and very heavy earth, which can only be obtained pure by chemical process. It is easily reduced to powder, and is soluble in all kinds of acids. To the taste it is harsh and caustic; and, if taken into the stomach, proves an extremely virulent poison. In some respects it agrees with the alkalies ([42]), particularly in its property of changing blue vegetable colours to green, and in corroding, like them, though with less energy, all kinds of animal substances. From these circumstances it has sometimes been denominated an alkaline earth. Saturated with sulphuric ([24]) and carbonic acid ([26]), it constitutes the minerals denominated sulphat and carbonat of barytes ([196]). It has been discovered to have a metallic base, which is called barium.
39. Strontian is an earth which, like barytes, is not found otherwise than in combination with sulphuric and carbonic acids. It occurs in various parts of the world, and, when purified, forms a porous mass of greyish white colour, acrid taste, and somewhat alkaline nature. This earth converts vegetable blue colours to green, but does not act so strongly on animal bodies as barytes, nor is it poisonous, like that substance.
40. Lime, the basis of all those substances which are denominated calcareous, is only to be obtained in a state of purity by artificial process. Combined with carbonic acid ([26]) it forms limestone ([140]), chalk, and marble; all of which are capable of being converted into lime by burning. Lime may also be obtained from oyster and other sea shells. When pure, it is of white colour, and moderately hard substance, though it is easily reducible to powder. Its taste is burning and acrid; and, like the alkalies, it changes vegetable blue colours to green. It has likewise the property of corroding and destroying animal substances. Lime, when pure, absorbs water rapidly, becomes hot, and falls into powder. Even if exposed to the open air it gradually attracts moisture, and assumes a powdery form; soon after which it becomes saturated with carbonic acid ([26]) from the atmosphere, and is thereby again converted into carbonat of lime ([140]). It occurs abundantly in almost every country, but always in combination with some acid, carbonic ([26]), sulphuric ([24]), boracic ([28]), fluoric ([27]), or phosphoric ([25]). This substance has a metallic basis, which has been denominated calcium.
41. Magnesia is a light and perfectly white kind of earth, of soft powdery appearance, without taste or smell, and somewhat more than twice as heavy as water. It is not found in this pure state in nature, but may be prepared from Epsom salt, which consists of magnesia in union with sulphuric acid ([24]). The slightly acrid taste that is perceptible in the magnesia used in medicine arises from a portion of lime which it contains. This substance does not dissolve in water, but is soluble in every kind of acid. It has the property of changing delicate blue colours to green.
ALKALIES.
42. Alkalies are substances which enter into the composition of several kinds of minerals, and are known by their property of changing the colour of blue vegetable juices to green, and by a peculiarly acrid, caustic, and nauseous taste, which it is impossible to describe, but which, after it has been once experienced, will easily be recollected. Alkalies corrode and dissolve animal substances, and unite with oil and fat in such manner as to form the well known compound called soap. They readily dissolve in water; and, when mixed with acids, form what have been denominated neutral salts.
43. The alkalies at present known are three in number; potash ([205]), soda ([200]), and ammonia ([207]). Of these the two former, although till lately they have been considered simple substances, have been shown by Sir H. Davy to have metallic bases.
SIMPLE COMBUSTIBLES.
44. By this term we are to understand all those mineral substances, capable of combustion, which have not been discovered to consist of more than a single component part. They are four in number; hydrogen, sulphur, phosphorus, and carbon.
45. Hydrogen, as its name imports, is a principal constituent part of water; for, singular as it may appear, that well-known fluid is formed by a combination of two species of air or gas, called hydrogen and oxygen ([21]), and in the proportion of about fifteen parts of the former and eighty-five parts of the latter. This gas had formerly the denomination of inflammable air, and has long been known in mines under the name of fire-damp. It is about twelve times lighter than atmospheric air. When pure it soon destroys such animals, and extinguishes all such flaming substances, as are immersed in it. Mixed with atmospheric air, it explodes with great violence on the application of any ignited body.
46. Sulphur is a simple combustible substance, of yellow colour, which is found pure, or native, in several parts of the world, and is sufficiently familiar to us under the name of brimstone ([211]). It strongly attracts oxygen ([21]), and is thereby converted into sulphuric acid ([24]). It frequently occurs in combination with mineral substances, such as arsenic, antimony, copper, and other metallic ores.
47. Phosphorus is a combustible substance which, when pure, somewhat resembles bees’-wax both in colour and consistence; and, when exposed to the air under the usual temperature of our atmosphere, is luminous in the dark, and has a smell somewhat resembling that of garlic. It is so combustible that, when melted, it should be kept under water, as it cannot be exposed to the air during this process without great risk of catching fire. This substance is not known in a native state; and the whole of what is used in philosophy and commerce is obtained by different artificial processes. In union with oxygen ([21]) it becomes converted into an acid, called phosphoric acid ([25]), and, under this form, in conjunction with lime, it constitutes the bones of men and animals. The greater part of the phosphorus of the shops is obtained from bones.
48. Carbon is a name given to the pure inflammable part of charcoal. It is abundantly diffused throughout nature, for it enters into the composition of several minerals, and of all vegetable and animal bodies. The purest form under which carbon is known to exist is in the diamond ([50]). It may, however, be obtained sufficiently pure, for all common purposes, by burning a piece of wood, covered with sand, in a vessel called a crucible. In combination with oxygen ([21]) it forms carbonic acid ([26]). Carbon is a chief component part of pit-coal ([217]), petroleum ([213]), and other bituminous substances.