Glucinum
Glucinum is a rare metal, silvery-white in color, malleable, and melting at a fairly low temperature. It is found in the mineral beryl, from which has come the alternative name beryllium. The name comes from the sweet taste of its salts. Except for beryl its minerals are rare, and the metal has found but few uses for man.
[Beryl]
Gl₃Al₂(SiO₃)₆
[Pl. 39]
Occurs in hexagonal crystals in granites, gneisses and mica schists; hardness, 7.5; specific gravity, 2.7; color usually some tint of green; luster vitreous; transparent on thin edges.
When this mineral occurs in coarse hexagonal prisms, with or without faces on the ends, it is known as beryl; when the crystals are clear and perfect and of a dark-green color, they are of gem value and are termed emerald; when of a light-green color, they are aquamarine; and when bright-yellow in color, they are the golden beryl. There is little difficulty in determining beryl, for only apatite occurs in such crystals, and is green, and this latter mineral has a hardness of only 5. There is an imperfect basal cleavage.
Ordinary beryl is fairly common in granites of the pegmatite sort, and less common in gneisses and mica-schists. This type often furnishes crystals of large size, up to two and three feet in diameter.
Beryl which is free from cracks and inclosures, so it can be used as a gem, is so rare, that the emerald has a value above that of the diamond, and second only to the ruby. It is one of the gems with a long history, having been quarried on the west coast of the Red Sea at least 1650 B.C. by the Egyptians. To early people it had a power to quicken the prophet instinct and made the wearer see more clearly. The Spanish conquistadores found fine emeralds among the treasures of both Mexico and Peru. In the United States, Stony Point, N. C., was a notable locality for these gems, but now seems to have been exhausted. The name emerald has been applied to many other green stones, usually with some geographical modification, as “Oriental emerald” which is green corundum, “Brazilian emerald” which is tourmaline, etc.
Giant beryls have been found at Acworth and Grafton, N. H., and at Royalston, Mass. Localities for ordinary beryl are Albany, Norway, Bethel, Hebron, Paris, and Topsham, Me., Barre, Goshen and Chesterfield, Mass., New Milford and Branchville, Conn., Chester and Mineral Hill, Penn., Stony Point, N. C., and many other localities in the Appalachians; also Mount Antero, Colo., and in the Black Hills of South Dakota.
[Sodalite]
Na₄Al₃Cl(SiO₄)₃
Occurs in irregular masses, sometimes in dodecahedrons; hardness, 5.5-6; specific gravity, 2.3; color deep-blue to colorless; streak white; luster vitreous; translucent on thin edges.
This striking mineral, with its deep-blue to azure color, is not easily confused with any other. It is characteristic of soda-rich igneous rocks such as syenite and some lavas. In this country it is found at Litchfield, Me., and Salem, Mass.
[Zircon]
ZrSiO₄
[Pl. 39]
Usually occurs in tetrahedral crystals in igneous rocks; hardness, 7.5; specific gravity, 4.7; color brown; luster vitreous; translucent on thin edges.
Zircon, the mineral of the rare earth element zirconium, nearly always occurs in light-colored igneous rocks, like syenite. It may occur in schists or gneisses, but in these rocks the crystals are of microscopic size. Because of their great hardness and insolubility, zircon crystals resist weathering and are often found, along with gold, cassiterite, or magnetite, in sands which have resulted from the disintegration of syenite rocks.
Zircon refracts and disperses light to a degree second only to the diamond, so that clear crystals are sought as gems. They are often called “Matura diamonds” because of their abundance at Matura, Ceylon. When the crystals are colorless or smoky they are termed jargons or jargoons; when of a red-orange hue, they are hyacinth or jacinth. Most of the zircon of gem-quality comes from Ceylon, where it is picked up as rolled-pebbles from the beds of brooks.
The most remarkable American locality for zircon is near Green River, in Henderson Co., N. C., where it is found abundantly in a decomposed pegmatite dike, from which many tons have been obtained. It is also found at Moriah, Warwick, Amity and Diana, N. Y., at Franklin Furnace, and Trenton, N. J., in the gold-bearing sands of California, etc.
[Cyanite]
Al₂SiO₅
[Pl. 40]
Occurs in long blade-like crystals in gneisses and schists; hardness, 7 at right angles to the length, and 4.5 parallel to the length; specific gravity, 3.6; color blue; luster vitreous; translucent on thin edges.
There are only a few blue minerals, and the way in which cyanite occurs in long thin blade-like crystals is entirely characteristic. If more is still wanted to determine this mineral, its unique character in having the great hardness 7 when scratched parallel to the length, and only 4.5 when scratched crossways, will settle any doubts.
The mineral sillimanite has the same composition as cyanite, but is fibrous in habit and has the hardness 6.5. If cyanite is heated to 1350° C. it changes its character and becomes sillimanite.
Cyanite is found as an accessory mineral in metamorphic rocks, such as gneiss and schist, at Chesterfield, Mass., Litchfield and Oxford, Conn., in Chester Co., Penn., in North Carolina, etc.
The [Mica] Group
The micas are very common minerals, easily recognized by their very perfect basal cleavage, as a result of which thin sheets, often less than a thousandth of an inch in thickness, readily split off. These are tough and elastic, which distinguishes mica from the chlorite group in which there is similar basal cleavage, but the sheets are not elastic.
Micas are complex silicates of aluminum, with potassium, iron, lithium, magnesium and hydrogen. They are one of the principle components of many granites, gneisses, and schists. This mineral is always crystalline, being in the monoclinic system, but occurring in six-sided prisms. The cleavage is so dominant a character that the crystal form is usually overlooked, as it is seldom requisite in determining this mineral. The size of the sheets of mica depend on the size of the crystals, the larger sheets expressing great slowness in cooling from the original magmas. Sometimes the crystals may be two or even three feet in diameter. The hardness is not great, ranging between 2 and 3. The specific gravity lies between 2.7 and 3.2. The color varies according to the composition, from silvery-white, through gray, pink, and green to black. The luster is vitreous to pearly, sometimes gleaming in the darker-colored varieties. The commoner types of mica are as follows:
Muscovite, H₂KAl₃(SiO₄)₃ or potash mica. Lepidolite, LiK(Al₂OH·F)Al(SiO₃)₃ or lithia mica. Biotite, (HK)₂(MgFe)₂Al₂(SiO₄)₃ or iron mica. Phlogopite, H₂KMg₃Al(SiO₈)₃ or magnesia mica.
Muscovite is colorless, silvery-white, gray or sometimes pale-green or brown. It gets its name from Moscow where it was early used for window panes, and it is still used for stove and furnace doors, as well as in electric work, for a lubricant, etc.
The best crystals occur in granites, in the coarse varieties of which large crystals may be obtained. It is found also as small scales in gneisses and schists, and when weathered from its original rocks it may be present in sandstones and shales. Muscovite is always in its origin an elementary component of deep-seated igneous rocks, like granite; but is never a component of extruded lavas. Sericite is muscovite which has been secondarily produced by the alteration of other minerals into muscovite, as when feldspar, cyanite, topaz, etc., have been modified by the presence of heat and hot vapors, when near lavas that have come in contact with other rocks. Muscovite is very resistant to alteration by weathering, but when it does change, the greater part of it becomes kaolin. It is found at Acworth and Grafton, N. H., in plates, sometimes a yard across at Paris, Me., Chesterfield and Goshen, Mass., Portland and Middletown, Conn., at Warwick, Edenville, etc., N. Y., and all down the Appalachian Mts., also in the Rocky Mts., the Cascade Range, etc.
Lepidolite is pink or lilac in color and occurs in scaly masses, mostly in granites. It does not come in large crystals. Lepidolite is found at Paris and Hebron, Me., Middletown, Conn., Pala, Calif., etc.
Biotite is dark-brown or black mica. Like muscovite it is very common, making one of the chief components of granites, gneisses and schists; and, unlike muscovite, it may occur in extrusive lavas, like trachyte, andesite, and basalt. It resists weathering much less than muscovite, so that, when the rocks of which it is a component disintegrate, biotite is usually altered to kaolin and other compounds. It is likely to occur in good-sized crystals, especially at Topsam, Me., Moriah, N. Y., Easton, Penn., etc.
Phlogopite is pale-brown, often coppery in color, and is most likely to occur in serpentines, or crystalline limestones or dolomites, often in fine crystals, of good size. While one of the less abundant micas, this is found at Gouverneur, Edwards, and Warwick, N. Y., Newton, N. J., and Burgess, Canada.
[Topaz]
Al₂F₂SiO₄
[Pl. 41]
Occurs in crystals mostly; hardness, 8; specific gravity, 3.5; colorless to pale-yellow; luster vitreous; transparent on thin edges.
Topaz may be colorless, but is more often some shade of yellow, and at times brown or even blue. Its hardness is characteristic, there being but few minerals as hard, and it is used to represent the hardness 8 in the Moh’s scale. The crystals are orthorhombic prisms, with the edges of the prism beveled and often striated. The ends of crystals usually terminate with a basal plane, parallel to which there is good cleavage. Between this basal plane and the prism faces there are usually several sets of small faces as indicated on [Plate 41].
This mineral, as is also true of most minerals containing fluorine, is one of those which have crystallized out from hot vapors, escaping from igneous magmas. It is associated with such minerals, as tourmaline, beryl, fluorite, and cassiterite, and occurs mostly in cavities or seams, in or near granites.
Ordinary topaz, which means crystals that are imperfect by reason of tiny cracks and impurities is not very rare, but crystals which are perfect and clear in color are considered gems. Most of the gem-topaz is some shade of yellow, but may be brown or blue, never, however, pink, as is often seen in jewelry. The “pinking” is artificial, and done by packing yellow or brown topaz in magnesia, asbestos, or lime, and then heating it slowly to red heat, after which it is cooled slowly. If underheated the color is salmon, if overheated all color disappears. Topaz has been a gem for centuries, the earliest records coming from Egypt. The name comes from topazios, meaning to seek, because the earliest known locality, from which it was gathered, was a little island of that name in the Red Sea, and this island was often surrounded by fog and hard for those early mariners to find. Here by mandate of the Egyptian kings the inhabitants had to collect topazes, and deliver them to the gem-cutters of Egypt for polishing.
Several yellow stones are called topaz, as the “Oriental topaz” which is corundum and more valuable than topaz itself; and several varieties of yellow quartz, which go under such names as “Saxon,” “Scotch,” “Spanish,” and “smoky” topaz. When topaz occurs colorless as in Siberia, the Ural Mountains, and in the state of Minas Geraes, Brazil, in all of which places it is found as pebbles in brooks, it goes under the name of “slave’s diamonds.” Brazil is today the chief source of gem-quality topaz.
Ordinary topaz is found in this country at Trumbull, Conn., Crowder’s Mt., N. C., Thomas Mts., Utah, in Colorado, Missouri, and California, etc.
[Staurolite]
FeAl₅OH(SiO₆)₂
[Pl. 41]
Occurs in orthorhombic crystals; hardness, 7.5; specific gravity, 3.7; color brown; luster resinous; translucent on thin edges.
This mineral occurs about equally abundantly in simple crystals similar to the outline on [Plate 41], and in twins which have grown through each other either at 90° or at 60°. The color is either brown or reddish-brown. In all cases it is an accessory mineral, occurring in metamorphic rocks, usually schists, though less frequently in slates and gneisses.
From the seventeenth century on, it has been used as a baptismal stone, and worn as a charm, legends stating that it fell from the heavens. Fine crystals have been found in Patrick County, Va., and there is in this region the legend, that when the fairies heard of the crucifixion of Christ, they wept and their tears falling crystallized in the form of crosses, such as the one shown on [Plate 41].
Staurolite is found in the schists of New England as at Windham, Me., or Chesterfield, Mass., and all down the east side of the Appalachian Mountains to Georgia.
[Olivine]
(MgFe)₂SiO₄
Peridot or Chrysolite
Occurs in grains and irregular masses in dark lavas; hardness 6.5 to 7; specific gravity 3.3; color bottle- to olive-green; luster vitreous; translucent on thin edges.
Olivine rarely occurs in crystals, but when it does they belong to the orthorhombic system. The dark-green grains or masses are recognized by the color, considerable hardness and indistinct cleavage. Serpentine may have a similar color, but its hardness is only 4. In hydrochloric acid olivine decomposes to a gelatinous mass.
Olivine is typically one of the constituents of the dark lavas, like basalt, gabbro, or peridotite. It is also a common mineral in meteorites. Olivine, in the presence of water, alters to other minerals, especially serpentine, with great facility.
It occurs fairly widely wherever the dark lavas are present, as in the White Mountains of N. H., in Loudoun Co., Va., in Lancaster Co., Penn., and in many localities in the Rocky Mountains and Cascade Range.
[Epidote]
Ca₂(AlOH)(AlFe₂)(SiO₄)₃
[Pl. 42]
Occurs in grains or columnar masses; hardness, 6.5; specific gravity 3.4; color green, usually a pistachio or yellow-green; luster vitreous; translucent on thin edges.
Rarely epidote occurs in crystals, which belong to the monoclinic system, and may be either short like the diagrams on [plate 42] or long and needle-like. The color and hardness will suffice to determine this mineral, as almost no other has the peculiar yellowish-green color which is characteristic of this form.
Epidote occurs primarily in metamorphic rocks at or near the contact with igneous rocks; or it may be a secondary mineral resulting from the weathering of granites, especially along seams. It sometimes occurs with hornblende in highly folded schists, as in New York City. It is often a mineral which has resulted from the alteration of other minerals, as pyroxene, amphibole, biotite, or even feldspars.
It is found at Chester and Athol, Mass., Haddam, Conn., Amity, Munroe and Warwick, N.Y., East Branch, Penn., in the Lake Superior region, in the Rocky Mountains, etc.
[Tourmaline]
(FeCrNaKLi)₄Mg₁₂B₆Al₁₆H₈Si₁₂O₆₃
[Pl. 42] & [frontispiece]
Occurs in three-sided prismatic crystals; hardness, 7; specific gravity, 3.1; colorless, red, green, brown, or black; luster vitreous; transparent on thin edges.
Tourmaline is readily distinguished from other minerals, as it always occurs in long to short prisms, which are three-sided in cross section. There is also a tendency for the sides to be curved as seen on the end view of D, [Pl. 42]. Frequently the vertical edges of the prism are beveled with one, two or three faces, grouped about each of the three original edges, and there are often striations on the prism faces. The ends are terminated by a low rhombohedron and again there may be a host of modifying faces on the edges and corners of the end. The common varieties are brown or black in color, but occasionally there may occur green, red, yellow or almost any color. When the crystals are perfect, that is free from impurities and without tiny cracks, tourmaline becomes a gem of popularity and value.
Tourmaline is very complex in composition and may vary considerably, the sodium, potassium, lithium, magnesium, and iron being either more or less abundant or even lacking. The color is to some extent dependent on the proportions of these elements present, the dark varieties having more iron, and the light colored tourmalines lacking it. This mineral is one of those which form from superheated vapors, escaping from molten magmas. It will therefore occur in veins, often associated with copper minerals, in crystalline limestones, or in cavities in granites, where it is associated with such minerals, as beryl, apatite, fluorite, topaz, etc.
If heated tourmaline crystals develop electricity, with the effect of making one end a positive and the other a negative pole, and then will attract bits of straw, ashes, etc. It was first introduced into Europe about 1703 from India, and its vogue as a gem has greatly increased since it was found on Mount Mica near Paris, Me. This Paris, Me., locality was discovered by two boys, amateur mineralogists, Elijah L. Hamlin and Ezekiel Holmes, who in 1820 were returning home from a trip hunting for minerals, when, at the root of a tree, they discovered some gleaming green substance. It proved to be gem-quality tourmaline. A snow storm that night buried their “claim,” but next spring it was visited and several fine crystals found. Later this locality was systematically worked, and over $50,000 worth of tourmaline taken from the pegmatite seam in the granite, which lay under the crystals found on the surface. The figure in the [frontispiece] is one of the crystals from there.
Well known localities are Paris and Hebron, Me., Goshen and Chesterfield, Mass., Acworth and Grafton, N. H., Haddam and Munroe, Conn., Edenville and Port Henry, N. Y., Jefferson Co., Colo., San Diego Co., Calif., etc.
[Kaolinite]
H₄Al₂Si₂O₉
Kaolin
Usually found in whitish clay-like masses; hardness, 2; specific gravity, 2.6; color white to grayish or yellowish; luster dull.
Kaolinite does not generally occur in crystals, though crystals of microscopic size and monoclinic forms have been found. It is a secondary mineral resulting from the decomposition by weathering of feldspars, the calcium, potassium or sodium having been replaced by water. When found in place it is generally white or nearly white, and is characterized by its greasy feel.
As granites or other feldspar-bearing rocks are weathered away, the kaolin is washed out by water, and with other fine material is carried down into lakes or the sea, where it settles to the bottom and is known as clay. Clay is kaolin with more or less impurities.
Pure kaolin is used for the manufacture of china and white porcelain ware; but when it is impure, especially when it has iron in it, baking causes the product to turn red or brown, so that it is only suitable for making tile, bricks, etc.
It is found almost anywhere that feldspar rocks are, or have been, exposed to weathering.
[Talc]
H₂Mg₃(SiO₃)₄
Occurs in scales, or in fibrous, scaly or compact masses; hardness, 1; specific gravity, 2.7; color white, gray or pale-green; luster pearly; translucent on thin edges.
This mineral is as soft as any, only graphite and molybdenite being of the same hardness, but both these latter two have a black streak, while the streak of talc is white. The greasy feel is also characteristic. Talc is very seldom found in crystals, but if they are found, they will appear like flakes and have a hexagonal cross section, though in reality they belong to the monoclinic system.
Talc is a secondary mineral which usually results from the exposure of magnesium silicates, such as pyroxenes or amphiboles, to moisture. In this case, in-as-much as the original rocks were metamorphic in origin, the talc therefrom will occur in old metamorphic regions. Some talc is also formed by the action of silica-bearing waters on dolomite. This is likely to be the case near the contact between dolomite and igneous rocks. Talc is closely related to serpentine and likely to be found in the same regions.
Talc has come to have a considerable use. Some of it is compact and then called soapstone, and this was used by the ancient Chinese to make images and ornaments; and our North American Indians used it to make large pots, to serve as containers for liquids. Some of these pots have been carved out with great skill, so as to be fairly light in proportion to what they would hold. Pipes and images were also carved from soapstone. Today we still cut soapstone into slabs to make mantels, laundry tubs and sinks. The scaly and fibrous varieties are ground, and used in making paper, paint, roofing, rubber, soap, crayons, toilet powders, etc. The United States produce and use over half the world’s production, our industries requiring over 100,000 tons of talc a year. Of this 38% goes into paper, 23% into paint, 18% into roofing, and so on down to toilet powder which uses 2½%, or 2,500 tons a year.
Talc is found in metamorphosed regions, that is in New England, all down the east side of the Appalachian Mts., in the Rocky Mts., and the Cascade Ranges, with a large number of local occurrences. New York State is the leading producer.
[Serpentine]
H₄Mg₃Si₂O₉
[Pl. 43]
Occurs in compact, granular or fibrous masses; hardness, 3; specific gravity, 2.6; color green; luster greasy; translucent on thin edges. Serpentine is never in crystals. Its color and hardness serve to distinguish it. Like talc it is a secondary mineral resulting from the alteration, in the presence of moisture, of pyroxenes, amphiboles, and especially, olivine. As these are often in metamorphic rocks, the serpentine is likely to be associated with metamorphic rocks. Some serpentine is also the result of the action of silica-bearing water on dolomite, and this is likely to occur in areas of sedimentary rocks. The fibrous variety of serpentine, chrysolite, usually occurs in seams or veins, and when the fibers are long, it is used as asbestos. This form of asbestos is the one most used commercially today, as there are remarkably large deposits of it in the Province of Quebec, which provide the major part of the world supply. In the United States it is also found in California and Arizona but only in moderate quantities.
Massive serpentine is used in considerable quantities as an ornamental stone, the green color varied with streaks and blotches of white, yellow and red, due to various impurities, making it very effective. It is, however, only suitable for interior work as the weather quickly spoils the polished surface. This is further discussed under serpentine rock, [page 245].
Serpentine is found at Newfane, Vt., Newburyport, Mass., Brewster, Antwerp, etc., N. Y., Hoboken, N. J., in Pennsylvania, Maryland, etc.
[Chlorite]
H₈(MgFe)₅Al₂(SiO₆)₃
[Pl. 43]
Occurs in monoclinic crystals of six-sided outline, or in scaly flakes or masses; hardness, 2; specific gravity 2.8; color green; luster pearly on cleavage faces; translucent on thin edges.
Chlorite is a family name, covering a series of closely related minerals, so similar in appearance that they are best considered under this common name. In many respects they resemble mica, in the shape of the crystals and the remarkable basal cleavage. At first glance it is easy to confuse the two, but chlorite scales are not elastic, and when bent, stay bent, instead of snapping back like mica. In fact they look like more or less rotted micas. This is more than appearance, for chlorites form as a result of the alteration of micas in the presence of moisture. They are then secondary, and will be found where mica-rocks have been weathered, as in granites and schists.
They may be expected anywhere that micas have been long exposed, as in New England, the Rocky Mountains, or the Sierra Nevada or Cascade Ranges. Special localities are Brewster, N. Y., Unionville and Texas, Penn., etc.