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.
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.
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.
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 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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The zeolites are a group of white minerals, with a pearly luster, light weight, and easy solubility in acids; which, because their contained water is lightly held, readily boil before the blowpipe. They are all secondary minerals, which result from the decomposition of feldspars, when exposed to weathering. They are almost universally found in seams and cavities of disintegrating lavas. From a group of a dozen or so, three are common enough to be considered here. They may be found by watching such places, as where trap rock is being quarried for road material, or being blasted for any reason.
Occurs as trapezohedrons in seams and cavities in lavas; hardness, 5.5; specific gravity, 2.2; colorless, white or pink; luster vitreous; transparent on thin edges.
Analcite usually occurs in the 24-sided form, known as a trapezohedron, as illustrated in figure A, Pl. 44; but it may also occur in cubes with the three faces of the trapezohedron on each corner. Small crystals are often colorless, but the larger ones are either white or pink, and are opaque. While the form is the same as that of garnets, the color, lesser hardness, and the occurrence in lavas will serve to distinguish this mineral. If placed in hydrochloric acid analcite dissolves to a gelatinous mass.
It is always found in seams and cavities in lavas, as at Bergen Hill and Weehawken, N. J., Westfield, Mass., in the Lake Superior region, etc.
Occurs as bristling crystals in seams and cavities in lavas; hardness, 5.5; specific gravity, 2.2; colorless; luster vitreous; transparent on thin edges.
Natrolite occurs as beautiful bristling tufts of needle-like crystals, each crystal an orthorhombic prism with a very low pyramid on the end. This mineral is so easily fusible that it can be melted in a candle flame, giving to the flame the characteristic yellow color due to sodium. In hydrochloric acid it dissolves to a gelatinous mass. It is always a secondary mineral in cavities and seams in disintegrating lavas, and the tuft-like manner of growth is so characteristic, that once seen, it will always be recognized.
Natrolite is found at Weehawken and Bergen Hill, N. J., at Westfield, Mass., in the Lake Superior region, etc.
Usually occurs in sheaf-like bundles of fibrous crystals; hardness, 5.5; specific gravity 2.2; colorless to white, yellow or brown; luster vitreous; transparent on thin edges.
Stilbite crystals are really monoclinic, but on account of almost universal twinning, appear as if orthorhombic. Like the two foregoing minerals, stilbite is found in the seams and cavities of disintegrating lavas. It is readily recognized by its habit of forming in sheaf-like bundles of fibrous crystals. It may also, but more rarely, occur in radiating masses. In hydrochloric acid it is completely dissolved. It is found in lavas, at Weehawken and Bergen Hill, N. J., in the Lake Superior region, etc.
Calcium is one of the most abundant of metals, but never occurs as such in nature, nor is it used as a metal by man. In its metallic form it is yellowish-white, and intermediate between lead and gold in hardness. Exposed to air it soon tarnishes by oxidation, and in water rapidly decomposes the water, forming the oxide. However, it has a great affinity for other elements, and makes a large number of minerals, the most important of which are calcite, aragonite, gypsum and fluorite, while it is an essential component of some garnets, anorthite, epidote, amphibole and pyroxene. It is very widely distributed as limestone, and is found in solution in most all natural waters, and in the shells and bones of many animals and some plants.
Occurs in well defined crystals in incrustations, and in stalactitic, oolitic, and granular masses; hardness, 3; specific gravity 2.7; colorless to white, or when impure, yellow, brown, green, red or blue; luster vitreous to dull; transparent on thin edges.
Next to quartz, calcite is the most abundant of all minerals, and occurs in an almost endless variety of forms, over 300 having been described. It belongs to the hemihedral section of the hexagonal system, the form of the crystals being all sorts of variations of the rhombohedron, and combinations of left and right handed rhombohedrons. The cleavage is entirely uniform, in three directions, parallel to the faces of the rhombohedron, and at an angle of 74° 55′ with each other. Crystals may occur in the form characteristic of the cleavage, but not often. The commonest forms are a more or less elongated scalenohedron, made by combining right and left handed rhombohedrons, so that the resulting pyramid is six-sided, as in figure C, Plate 45. Such a scalenohedron may be combined with other forms in a great variety of ways. The six-sided prism with the ends terminated by one or more sets of rhombohedral faces is also fairly common. Twinning occurs occasionally.
The quickest way to determine calcite is by the hardness (3), combined with the fact that it effervesces, when hydrochloric acid is dropped upon it.
An interesting feature of this mineral is its marked property of deflecting light rays, so that a line or object placed behind a piece of clear calcite appears double. It was with pieces of calcite from Iceland that this was first seen; so that large transparent crystals of calcite are still called Iceland spar; and such calcite is used to make the Nichol’s prisms for microscopes, which are so useful in the study of minerals. This power of refracting light is present in all minerals, but not to such a marked degree as in calcite. The elongated scalenohedrons of calcite are often called “dog-toothed spar” from a fancied resemblance between them and the dog’s tooth.
Calcite is present in solution in the water of the sea and most streams, from which it is withdrawn by many animals and some plants, to make their shells, and bones. The foraminifera, some sponges, the echinoderms, corals and molluscs all draw large quantities from the water in which they live, and build more or less permanent structures from it. These shells when they fall to the bottom, or after being broken to bits, accumulate on the bottom and make limestone, which is widely distributed over the country. This same limestone, when metamorphosed and crystalline, is marble.
Calcite then is readily soluble in water, and streams flowing along crevices and fissures in limestone dissolve out great cavities or caves, like the Mammoth Cave of Kentucky. Other water, percolating through the limestone, comes to these cavities saturated with lime in solution and drips from the roofs and walls; then as part of the water evaporates, it deposits part of its lime in icicle-like masses, hanging from the roof. Such masses of non-crystalline calcite are called stalactites. Below on the floor of the cave, conical masses are built up in the same manner where the dripping water falls on the floor. These are stalagmites. In these limestone caves and in smaller cavities many of the most beautiful crystals grow. Somewhat similarly, when hot water from deep springs comes to the surface, it cools and can not carry as much lime, and so around the spring is laid down layer after layer of non-crystalline calcite making a mass known as travertine. Sometimes this is colored by iron or other impurities and a banded effect results. Such travertine as the “Suisun marble” from California, “California onyx,” “Mexican onyx,” and “satin spar” all belong to this class.
The coral animals, especially in tropical waters precipitate an enormous amount of lime, until whole reefs are built of lime in this non-crystalline form. In places it is hundreds of feet thick and hundreds of miles in extent. Some of this coral has become popular for personal adornment. This is particularly a small, fine-grained variety, Corallum rubrum, which lives almost exclusively in the Mediterranean Sea. This coral is red in color, varying all the way from a deep red to white. It grows in small masses, three pounds being a good sized mass, in water 60 to 100 feet deep, requires some ten years to develop a full-sized mass. The making of this into beads and ornaments is an Italian industry. The demand is growing, while at the same time the supply is diminishing, and search is being widely made for more such coral, but up to the present time with little success. This precious coral is much worn as a protection against the “evil eye” and is widely imitated, apparently with as much protection to the wearer. When coral beads are offered cheap, they are probably something else, red gypsum being much used. This and all imitations can be readily detected by trying a drop of acid in the bead. Coral will effervesce, but gypsum and other substitutes will not.
The bulk of the shells of most molluscs is made of lime, but the mother-of-pearl layer inside is usually aragonite. The chalk of the cliffs on either side of the English channel is lime, and composed of the shells of single celled animals. See p. 213. When lime is deposited in loose porous masses, as around grass, etc., and below hot springs, this mass is termed calcareous tufa.
Calcite will be found almost everywhere, some of the localities for the finest crystals being Antwerp and Lockport, N. Y., Middletown, Conn., the caves of Kentucky, Warsaw, Ill., Joplin, Mo., Hazel Green, Wis., etc.
Occurs in crystals, in columnar or fibrous masses, or incrustations; hardness, 3.5; specific gravity, 2.9; colorless, white or amber; luster vitreous; transparent on thin edges.
Aragonite has the same chemical composition as calcite, but it crystallizes in the orthorhombic system, either in simple forms like A on Plate 46, or twinned, so as to make forms which seem hexagonal. When in simple crystals its form easily distinguishes it from calcite and dolomite, but when twinned it appears much like either of these two minerals. From calcite it can then be distinguished by its greater hardness and the fact that it has cleavage in one direction only, and that imperfect. The cleavage is the only easy method of distinguishing it from dolomite. However, aragonite is most always easily distinguished by its habits, for it generally forms long slender crystals, which appear more like fibers than crystals. Neither calcite nor dolomite is at all fibrous.
Aragonite is much less abundant than calcite, and has resulted, either from deposition from hot waters, or from waters having sulphates in solution as well as lime. Much of the travertine, and many stalagmites and stalactites are composed of aragonites, forming as outlined under calcite. The mother-of-pearl layer in the shells of bivalves is generally aragonite. The pearly luster of this layer is due to its being formed by the successive deposition of one thin layer upon another; so that light falling on the mother-of-pearl, penetrates, part of it to one layer and part to another, and is then reflected. Certain molluscs have this layer composed of especially thin layers, one, the Unios or freshwater clams, the other, the “pearl oysters” or Aviculidæ, these latter, however, being only distantly related to the edible oysters. In the cases, where molluscs of either of these two families are of large size, large pieces of mother-of-pearl can be recovered, and are used for buttons, handles, and various ornamental objects. A further peculiarity of these same molluscs is the formation of pearls in the sheet of flesh, lining the shells. The pearls are round or rounded concretions of aragonite. At the center there is a grain of sand, or more often a tiny dead parasite. Either was an irritant to the mollusc, and to be rid of it, a layer of aragonite was secreted around it. Then as the mollusc continued to grow and secrete layers for its shell, it also added each time another layer around the sand-grain or parasite, until in time a pearl of noticeable, and then of considerable size resulted. These have all the pearly luster of the mother-of-pearl in a sphere which tends to make the luster even more marked.
Pearls were in use as ornaments in China some twenty-three centuries before Christ, and in India over 500 B.C. They were very highly prized by the Romans and since their times the rulers of India have shown a remarkable fondness for them. Today the finest come from the Gulf of Persia and the Red Sea, while still others are found about Australia and in the Caribbean Sea. In the United States not a few are collected every year from the fresh water clams, some of them beautifully tinted with pink or yellow.
Aragonite is found widely, as at Haddam, Conn., Edenville, N. Y., Hoboken, N. J., New Garden, Penn., Warsaw, Ill., etc.
Occurs in cleavable or granular masses, rarely in crystals; hardness, 3-3.5; specific gravity, 2.9; color white, gray, bluish or reddish; luster pearly on cleavage faces; transparent on thin edges.
When anhydrite occurs in crystals, they are orthorhombic, like the diagram on Plate 46. Usually, however, it is found in beds or layers, which were deposited by the evaporation of sea water, and so it is associated with salt. Anhydrite has three cleavage planes which are at right angles to one another, which produce rectangular or cube-like forms. Mostly anhydrite is associated with gypsum, from which it differs by its greater hardness, pseudo-cubic cleavage, and the fact that anhydrite is not readily soluble in acid, while gypsum is. Chemically it differs from gypsum in not having water of crystallization, which gypsum does have. The anhydrite is likely to occur as veins and irregular masses in beds of gypsum. Calcium sulphate is precipitated from sea water when 37% of the water has been evaporated, and it may be deposited either as anhydrite or as gypsum, the factors, which decide as to which of these two minerals it will be, being as yet unknown. After deposition, if exposed to moisture, the anhydrite may change to gypsum, irregular masses often remaining unchanged.
It is found in salt mines in Elsworth Co., Kan., in limestone cavities at Lockport, N. Y., in veins in Shasta Co., Calif., etc.
Occurs in crystals, in cleavable masses, or in fibrous masses; hardness, 2; specific gravity, 2.3; colorless, white, amber, gray, or pink; luster vitreous, silky or pearly; transparent on thin edges.
Gypsum crystals are monoclinic as seen on Plate 47, the perfect ones usually occurring in clay, as at Oxford, O., or in cavities; while crystals of less perfect outline, but with fine cleavages, are found in Utah, Kansas, and Colorado. The cleavage is very perfect in one direction, making it possible to strip off thin sheets almost like mica, and less perfect in two other directions, which appear on the smooth surface of the first cleavage as lines intersecting at 66° 14′. Twinning is also common in such a way, that the two united crystals make forms similar to arrowheads. These cleavages and the twinning show nicely in the photograph of gypsum on Plate 47.
Gypsum is distinguished from anhydrite by its lesser hardness, its cleavage and by being soluble in acids.
Most gypsum occurs in beds or granular masses which were deposited from evaporating sea-water, coming down when 37% of the water was lost. Such beds are often very extensive and are quarried as a source of gypsum to make plaster of Paris, stucco, neat plaster, Keene’s cement, plaster and wall board, partition tiles, etc. The use of the gypsum for plaster of Paris and all these other uses is based on its affinity for water of crystallization. The gypsum is first heated to about 400° C., which drives off the water of crystallization, and causes it to crumble to a powder, which is the plaster of Paris. When water is added, it is taken up and the powder “sets,” or recrystallizes back to gypsum. This simple reaction has made it very useful, for making moulds, casts, hard finish on walls, as stucco, etc.
When the granular type of gypsum is fine grained, it is known as alabaster, which is used for carving vases, statuettes, ornaments, etc. The fibrous variety is called satin spar, and is sometimes used for cheap jewelry and ornaments, but it is very soft and quickly wears out. At Niagara Falls there is a considerable trade in objects carved from this satin spar, tourists buying them on the assumption that the mineral is native and comes from under the falls. Most of it, however, comes from Wales, the small amount of gypsum of that region being mostly granular.
Gypsum is found all across the United States, as in New York, Michigan, Virginia, Ohio, Alabama, South Dakota, Wyoming, Colorado, Utah, California, etc.
Strontium is a pale-yellow metal, ductile and malleable, but oxidizing quickly when exposed to the air. It does not occur in its native state in Nature, but always as some compound, usually either the carbonate or sulphate. It resembles barium, but differs in giving to the flame a brilliant red color, on which account the compounds of strontium are used mostly in making red fire in fireworks.
Occurs in needle-like crystals, or in columnar or fibrous masses; hardness, 3.5-4; specific gravity, 3.6; color white, pale-green or pale shades of yellow; luster vitreous; transparent on thin edges.
Strontianite is orthorhombic, but appears as if hexagonal, since its general habit is to have three twin crystals grow together in such a way as to make a six-sided double pyramid. In this it is very like witherite, both these minerals appearing externally much alike. They can be readily distinguished, however, by holding a piece in the flame. If it gives a red color to the flame it is strontianite, if green, it is witherite. It effervesces readily in hydrochloric acid.
Strontianite is found in veins and cavities in limestone, where it has been deposited after being leached from the limestone by percolating waters. Though known at several localities it is not now being mined in this country, what we use being imported mostly from Germany.
It is found at Schoharie, Chaumont Bay and Theresa, N. Y., in Mifflin Co., Penn., etc.
Occurs in crystals, cleavable masses and fibrous; hardness, 3; specific gravity, 3.9; colorless, white, pale-blue, or reddish; luster vitreous; transparent on thin edges.
Celestite, the sulphate of strontium, is very like barite in external appearance and habit. It is orthorhombic and occurs in tabular crystals. Its cleavage is perfect on the basal plane, and imperfect in one other direction. The ready way of distinguishing celestite from barite is to hold a piece in the flame. If it is celestite it will color the flame red, if barite, green.
Celestite is mostly found in veins or cavities in limestone, where it has been deposited by percolating waters, after having been leached from the limestone. Some years ago an important deposit of celestite was found on Strontian Island in Lake Erie, but that was soon worked out and now no veins are being worked in this country. It is also found at Chaumont Bay, Schoharie and Lockport, N. Y., in Kansas, Texas, West Virginia, Tennessee, etc.
Barium is another metal which does not occur in its native state in Nature. It has only been isolated as a yellow powder, which, exposed to air or water, soon changes to one of the oxides. Both barium and its compounds are peculiar in causing a green color, whenever exposed to the flame. Two of its compounds are fairly abundant, the sulphate, barite, and the carbonate, witherite. The former is the more abundant and has come to be fairly widely used, something over 100,000 tons being annually consumed in the United States, to make the body in flat finish paints for interior work and light colors, for a filler in rubber goods, linoleum, oil cloth, glazed paper, and for a wide range of chemical compounds.
Occurs in crystals or in lamellar, nodular or granular masses; hardness 3; specific gravity, 4.5; colorless, white or almost any color; luster vitreous; transparent on thin edges.
Barite occurs in orthorhombic crystals, which are tabular in form, and usually have the edges beveled, as in figure A, Plate 48. There is cleavage in three directions, a rather perfect basal cleavage, and two less perfect cleavages, which are at right angles to the basal cleavage plane, and intersect each other at 78°.
The tabular form, the cleavage, the heavy weight, and the fact that a piece of barite put into the flame colors it green, all serve to distinguish this mineral.
Barite is a secondary mineral of aqueous origin, which has been deposited in veins and cavities in igneous, metamorphic, or sometimes sedimentary rocks. It is most likely to occur in veins in igneous or metamorphic rocks, the barium having been dissolved from certain feldspars and micas by percolating water, and then redeposited in the fissures, as the water came into them. If in sedimentary rocks, the barite veins are usually in limestones. Barite is quite likely to be a gangue mineral for the ores of lead.
It is found at Hatfield and Leverett, Mass., Cheshire, Conn., Pillar Point, N. Y., Cartersville, Ga., in Virginia, North Carolina, South Carolina, Missouri, Kentucky, Tennessee, Alabama, Illinois, Wisconsin, Nevada, California, Alaska, etc.
Occurs in crystals, or in granular or columnar masses; hardness, 3.5; specific gravity, 4.3; color white to gray; luster vitreous; translucent on thin edges.
Witherite is not an abundant mineral. Its crystals are really orthorhombic, but they are usually twinned, three crystals growing through each other in such a manner that the resulting crystal appears like a six-sided double pyramid, similar to the one figured on Plate 48. The commonest mode of occurrence is in compact masses. Witherite effervesces when cold acid is dropped upon it, which, with its heavy weight, and the green color it gives to the flame, serves to distinguish the mineral. It is used for medicines, in chemical industries, and a considerable amount is made into rat poisons. The chief locality for witherite is in northern England, but in this country it is found along with barite, especially at Lexington, Ky., and in Michigan.
Carbon is an element widely distributed in nature, occasionally appearing in its elementary form, as graphite or the diamond, but much more important in its compounds. Small quantities are present in the air as carbon dioxide, CO₂, immense quantities occurring in the carbonate minerals, which have been considered under their respective metallic salts, as calcite, malachite, siderite, cerrusite, smithsonite, witherite, etc., and still other large quantities being represented in organic compounds, which occur as rocks under the heads of petroleum, coal, etc. The occurrence of limestones, graphite, coal or petroleum is always indicative of the activity of living organisms, and in some cases is the only indication of life in the earlier rocks.
Occurs in hexagonal scales or flakes, in layered masses, or earthy lumps; hardness, 1; specific gravity, 2.1; color black or steel-gray; streak gray; luster metallic; opaque on thin edges.