Sunstone or avanturine felspar is a variety of oligoclase; grayish-white to reddish-gray in color, usually the latter; containing minute crystals of hematite, göthite or mica, which are imbedded and scattered through the stone, and give forth golden-yellow, reddish, or prismatic reflections. The hardness is 6 to 7, specific gravity 2.56 to 2.72, and lustre pearly or waxy to vitreous.
Sunstones are found near Stockholm, in Finland, the Urals, Ceylon, the Alps, Iceland, the United States, and other places.
The Amazon stone is a green variety of felspar, which was first found on the banks of the Amazon River, but now comes from Siberia and the United States. This stone consists of potash, alumina, and silex—is green in color but rarely clean, being discolored in places and usually covered with small white spots.
The Amazon stone is harder than glass, but is scratched by rock crystal. Its specific gravity is 2.5 to 2.6; acids do not affect it, and it melts with difficulty before the blow-pipe.
Labrador stone or labradorite is sometimes known as opaline felspar, and was first discovered on the island of St. Paul on the coast of Labrador.
Labradorite is translucent to opaque, gray-green or brown in color, andhas beautiful chatoyant reflections of brilliant blue, sea-green, and sometimes red and yellow, changing from one color to another. Labradorite is 6 in hardness, has a specific gravity of 2.62 to 2.76; a vitreous to pearly lustre, is brittle, fuses with difficulty before the blow-pipe, and is decomposed by muriatic acid. It is composed of:
Large masses of this stone are found on the coast of Labrador. It is also found in Finland, Russia, and the United States. Because of the dark chatoyant appearance the name of œil de bœuf or ox-eye is sometimes applied to labradorite. Handsome specimens, cut cabochon, form pretty ring stones, and many effective engraved cameos have been produced by using the bright portion for the relief work and the gray dead part for the base.
This stone is the transparent variety of disthene, and is sometimes commercially known as sappare. Cyanite is colorless to bluish-white, sky-blue, berlin blue, yellowish- and reddish-white, gray, and green.
The hardness is 5 to 7, specific gravity 3.45 to 3.70, lustre vitreous and pearly; it is infusible before the blow-pipe, but fuses with borax; is not attacked by acids, and is composed of:
Cyanite is found in Switzerland, the Tyrol, Styria, Carinthia, Bohemia, Norway, Finland, France, South America, Scotland, Ireland, Siberia, the East Indies, and the United States. Clean specimens are not plentiful, and fine blue pieces have frequently been sold for sapphires. The cyanite can be distinguished from the sapphire by its inferior hardness and lighter weight.
Lapis lazuli, the sapphire of the ancients, is a mineral, translucent to opaque, ranging in color from colorless to an azure-blue, violet-blue, green, and red.
The principal color, however, is a rich, azure blue, sometimes shading into green, and having a vitreous to greasy lustre.
Its hardness is 5 to 5.5, specific gravity 2.38 to 2.42; it is decomposed by muriatic acid, and fuses before the blow-pipe to a white glass. It is rarely found clean, but has usually a number of veins and spots of a metallic nature. It is composed of:
This mineral is found in Siberia, Transylvania, Persia, China, Thibet, Tartary, South America, India, and Brazil.
Lapis lazuli is sometimes employed for jewelry, and was for somecenturies ground up and used to make the mineral paint known as genuine ultramarine. This paint is now produced chemically, and the more costly mineral compound is rarely used.
The imitation of lapis lazuli for jewelry purposes is also very easy, as metal filings can be readily introduced into the azure blue glass, and thus an imitation of the genuine stone produced, which is perfect excepting in hardness.
The hiddenite is a variety of spodumene that has only been found in one locality, namely, Alexander County, North Carolina. This mineral was discovered by W. E. Hidden, and has been named after him.
The hiddenite is perfectly transparent, and varies from a pale yellowish- to a deep emerald-green, being very brilliant, and approaching the emerald in color. As this stone is rarely found large enough for cutting into gems, it is highly prized, and good specimens command a large price.
The hardness of the hiddenite is 6.5 to 7, and specific gravity 3.13 to 3.19; before the blow-pipe it melts to a clear glass, and it is attacked by salts of phosphorus. It is composed of:
Spodumene is sometimes cut and polished as a gem, but its peculiar cleavage makes it a bad stone for the lapidary to cut and the jeweler to mount.
Its hardness is 6.5 to 7, specific gravity 3.13 to 3.19, and lustre, vitreous to pearly.
Grayish-green, greenish-white, and sometimes yellow or faint red are the colors. Its composition is:
Acids do not attack spodumene, and under the blow-pipe it fuses to a white glass.
This mineral is found in Sweden, the Tyrol, Ireland, Scotland, and the United States.
Dichroite is sometimes known under the mineralogical names of cordierite and iolite, and commercially assaphir d’eau, or water sapphire. This stone is remarkable for pleichroism, sometimes showing three different colors in as many directions, and when properly cut has often the star formation of the corundum star-stones.
Water sapphire, as the blue specimens are called, is 7 to 7.5 in hardness, specific gravity 2.56 to 2.67, transparent to translucent, and frequently full of flaws. It is partially decomposed by acids, melts with difficulty before the blow-pipe, is vitreous to greasy in lustre, and is composed of:
Besides thesaphir d’eau, which is blue, dichroite occurs colorless, bluish-white, yellowish-white, yellowish-gray to yellowish-brown, indigo to blackish-blue, and violet. This mineral is found in Ceylon, Spain, Norway, Sweden, Tuscany, Greenland, and Bavaria. Sapphire is harder and much heavier than dichroite.
Idocrase or vesuvianite was first found amongst the ancient ejections of Vesuvius, and it is still found at Vesuvius in hair-brown to olive-green colors.
Vesuvianite is 6.5 in hardness, 3.35 to 3.45 in specific gravity, transparent to opaque, lustre vitreous to greasy. It possesses strong double refraction, is attacked by acids, and melts readily under the blow-pipe. Vesuvianite consists of:
In colors, this mineral shades from brown to black, yellow, pale-blue, and green, and it is found at Vesuvius, Alps, Piedmont, Mt. Somma, Etna, Norway, Sweden, Spain, Hungary, Urals, and the United States.
Transparent or strongly translucent specimens, in handsome green or brown varieties, are used for jewelry, principally, however, in Turin and Naples.
Chrysolite and green garnet are sometimes substituted for vesuvianite. The first has a greater specific gravity and is more vivid in color, and the latter is also heavier and harder.
Euclase is very brittle, and therefore is rarely used as an ornamental stone.
This mineral has the hardness of 7.5; specific gravity, 3.1; lustre, vitreous to pearly; it is transparent to semi-transparent, doubly refractive, is not acted upon by acids, fuses under the blow-pipe to a white enamel, and is composed of:
Euclase occurs in Brazil, in the neighborhood of Villa Rica, and also in the Urals, in colorless, pale green, blue, pale yellow, and white colors.
Sphene or titanite is also a brittle mineral, 5 to 5.5 in hardness; specific gravity, 3.4 to 3.56; transparent, doubly refractive; lustre, adamantine to resinous; colors, brown, gray, yellow, green, black, and colorless; and composition:
When transparent in colorless, greenish, or yellow colors, this mineral presents an appearance like the fire opal.
Sphene is found in Switzerland, the Urals, Tyrol, Finland, Wales, Ireland, Germany, Canada, and the United States.
This mineral, rarely used as a gem stone, is 7.5 to 8 in hardness; specific gravity, 2.96 to 3; lustre, vitreous; transparent to semi-translucent, doubly refractive, it does not melt before the blow-pipe, and contains:
Phenacite occurs colorless, and also bright wine-yellow inclining to red, and brown. This stone is found in Russia, Mexico, and Alsace.
The colorless or transparent variety approaches the diamond in brilliancy, especially under artificial light.
Epidote usually occurs in a peculiar yellowish-green, called pistachiogreen, a color that is seldom found in other minerals. Besides this color, olive, brownish-green, greenish-black and black, red, yellow-gray, and grayish-white occur. The hardness of epidote is 6 to 7; specific gravity, 3.32 to 3.50; lustre, vitreous to pearly; refraction, double. The stone is transparent to opaque, is attacked by acids, and is slightly affected by the blow-pipe. It is composed of:
Epidote is found in Norway, Saxony, Siberia, Brazil, on the St. Gothard, in Switzerland, in the Tyrol, and in the Hartz.
Axinite is a brittle mineral which has occasionally furnished some pretty gem stones.
The hardness of this stone is 6.5 to 7; specific gravity, 3. to 3.3;lustre, vitreous. It is transparent to translucent, is not attacked by acids, and melts readily before blow-pipe. It is composed of:
Axinite occurs in clove-brown, plum-blue, and pearl-gray, and exhibits trichroism. The best specimens come from St. Christophe in Dauphiny, but it is also found at Santa Maria, and in Switzerland, Sweden, England, Chili, Saxony, the Hartz Mountains, and the United States.
Axinite is usually cut, like the opal, cabochon, but is rarely used as a gem stone.
Diopside is cut and sometimes sold in Turin and in Chamouny as a gem stone, but no great quantity of this mineral is used for ornamental purposes.
The hardness of diopside is 5 to 6; specific gravity, 2.9 to 3.5; lustre, vitreous to greasy. It is transparent to translucent, brittle, cannot be dissolved by acids, and melts before the blow-pipe. It is composed of:
This mineral is grayish-white to pearl-gray, and greenish-white to greenish-gray. The best green transparent specimens are from the Mussa Alp and Zillerthal, but it is also found in the Urals and the United States.
This mineral occurs in many colors, often approaching the finer gems in appearance, and bearing the commercial names of false ruby, false emerald, false topaz, etc., etc., according to its color.
Fluor spar is brittle, 4 in hardness, has the specific gravity of 3.1to 3.2, single refraction, is transparent to translucent, has a vitreous lustre, phosphoresces when heated, is attacked by acids, and melts before the blow-pipe. It is composed of:
White, yellow, green, rose- and crimson-red, violet-blue, sky-blue, and brown, wine-yellow, greenish-blue, and gray are the colors of this many-tinted mineral.
Fluor spar is found in England, Norway, Baden, Nova Scotia, Thuringia, the Alps, Saxony, and the United States.
Large pieces of this mineral are made into beautiful vases and ornaments.
Handsome specimens of hypersthene or Labrador hornblende are used for ornamental purposes.
This mineral is found in crystalline masses, has the hardness of 6, specific gravity 3.3 to 3.4, lustre pearly to metallic. It istranslucent to opaque, brittle, and fuses before the blow-pipe. It consists of:
Hypersthene occurs in dark-brown, green, grayish-black, greenish-black, and jet-black colors, and is found in the isle of Skye, the Hartz Mountains, Saxony, Labrador, Greenland, Norway, Sweden, Bohemia, Thuringia, and the United States.
The quartz group is the largest and most diversified among precious stones. Quartz occursmassive, in concretions, and in confused crystalline masses.
On account of the abundance of the massive kinds, such as jasper, agates, onyx, etc., some writers place the quartz group under the head of semi-precious stones, and lately the United States customs authorities have gone further in that direction, and have ruled that“because of the abundance and comparative cheapness of agates, onyxes, etc., they were no longer precious stones.” This position, however, the custom-house speedily abandoned, and, for dutiable purposes at least, the quartz family, in all its ramifications, is recognized as belonging to the precious stones.
Harder than the tourmaline, turquois, or opal, as hard as the chrysolite, and nearly as hard as the garnet or emerald, there is no reason why the crystallized varieties, such as amethyst, cairngorm, false topaz, chrysoprase, and even the cat’s-eye and finer onyxes, should not be classed among the precious stones.
Some more plentiful and less beautiful varieties of quartz are not valuable, and they take the same position in the quartz family that the huge imperfect crystals do in the beryl group. Whenever the specimen is sufficiently beautiful to be cut and polished for setting in jewelry, it should be included under the precious stones.
Quartz crystallizes in the rhombohedral system, and many varieties are found massive and compact. The cleavage is indistinct but can sometimes be found by plunging a heated crystal into cold water. The hardness of quartz is 7; specific gravity 2.5 to 2.8, the purest kinds being 2.65; the lustre is vitreous to resinous, and fracture conchoidal.
Quartz is tough, brittle, and feels cold; it becomes positively electric by rubbing, shows phosphorescence in the dark, and gives sparks if struck with another piece of quartz or with steel.
Quartz is transparent to translucent, semi-translucent to opaque, doubly refractive, and does not melt before the ordinary blow-pipe, but may be melted with the oxyhydrogen blow-pipe. It also melts with soda to a clear glass, and is soluble in fluohydric acid.
Quartz is composed of pure silica
Some of the impure varieties contain oxide of iron, carbonate of lime, clay, and other minerals.
Colorless quartz or pure rock-crystal is found in many parts of the world, notably in Switzerland, Dauphiny, Piedmont, the Carrara quarries in Italy, Canada; in Herkimer County, New York, and on the shores of Lake George, in the same place; at Hot Springs, Arkansas; and along the beach of Long Branch, Cape May, and many other places.
Rock-crystal, commercially known as Bohemian diamond, occidental diamond, Lake George diamond, rhinestone, pebble, etc., etc., is colorless and transparent. This stone is largely used for optical purposes, and is also sometimes cut into brilliants to imitate the diamond.
While rock-crystal is considerably harder than strass or paste, it lacks, however, the brilliancy of the fine-composition imitation diamond.
Besides being much softer, the paste is often heavier than the crystal, because of the quantity of lead and other minerals used in its composition.
Amethystine quartz or amethyst varies in color from light to clear-dark purple, sometimes nearly black, and from light to dark bluish-violet. The coloring of the stone is supposed to be due to manganese.
The best amethysts come from Brazil and Ceylon, but good specimens are found in India, Persia, Botany Bay, Transylvania, near Cork and the island of May in Ireland, at Oberstein, in Saxony, in Hungary, Siberia, Nova Scotia, Sweden, Bohemia, Canada, and in the States of Maine, Pennsylvania, Colorado, Georgia, Virginia, and Michigan.
Under heat, the amethyst turns first yellow, then green, and finally becomes colorless. The value of an amethyst depends upon the fashion,and the time has been when these stones ranked among the most valuable of precious stones. At present, a fine amethyst can be bought for very little money, but should the stone become fashionable again, the best specimens will command good prices.
Yellow quartz, known as false topaz, Bohemian, occidental, Indian, or Spanish topaz, resembles the real topaz in color, but is softer, lighter, different in crystallization and cleavage, and in electrical properties.
In color, this stone varies from the lightest yellow to orange-red and brown.
Most of the yellow quartz comes from Brazil, and much of it is changed to yellow by burning amethyst and smoky quartz.
Smoky yellow to smoky brown, often gray and black, are the tints of thecairngorm. This species of transparent quartz takes its name from Cairngorm in Invernessshire, in Scotland, a locality where some of the best specimens have been found. Pike’s Peak, Arkansas, and certain districts in North Carolina have also produced some very fine smoky topazes.
The cairngorm is used for seals, beads, and some of the cheaper jewels, and is largely sold at watering-places in Switzerland, and in the Western United States.
The stone is very popular in Scotland. Hair or needle stones is the name given to these varieties of crystallized quartz when they contain foreign substances, such as rutile, manganese, chlorite, etc., in hair or needle formation.
These stones are cut to represent the needle enclosures in an upright position, and are called sagenite or Venus hair stones or love arrows.
Iridescent or rainbow quartz is the variety of rock-crystal containingcracks and fissures which reflect all the colors of the rainbow. Quartz can also be artificially colored by rapidly cooling a heated specimen and then dipping the piece into a coloring preparation; the minute cracks in the quartz absorb the coloring matter, and the result is a red-, blue-, or green-tinted stone.
The massive varieties of quartz embrace the rose quartz, avanturine, cat’s-eye, crocidolite, heliotrope, chrysoprase, prase, plasma, chalcedony, agates, onyx, carnelian, jasper, hornstone, and flint.
Rose quartz occurs in a massive form, usually very imperfect and cracked, and varying in color from rose-red to pink. The color is supposed to be due to titanic acid, and often becomes paler on exposure.
This stone is nearly opaque and semi-transparent on the edges, has a greasy lustre, and specific gravity of 2.65 to 2.75. Rabenstein nearZwiesel in Bavaria, the United States, Brazil, France, Ceylon, Finland, and Siberia are places where rose quartz has been found.
Avanturine is an opaque, yellow, brown, or red quartz, spangled with minute scales of mica or some other mineral, and found principally near Madrid, in Spain. It is also found in France, Scotland, Bavaria, the Urals, and Styria.
A beautiful imitation of avanturine, called goldstone, is manufactured of glass into which metal filings are introduced. This goldstone is superior to avanturine in every point except that of hardness. Avanturine and its imitation, but largely the latter, are used for the cheaper kinds of jewelry, and were very popular in the United States some years ago.
The Hungarian, occidental, or quartz cat’s-eye is found on the coast of Malabar, Ceylon, Hartz Mountains, and Bavaria.
This stone is translucent to opaque, gray, green, brown, red, and the shadings of these colors, but usually a greenish-gray, with a mass of fine white lines in the centre, which give to the stone a chatoyant appearance.
The cat’s-eye is usually cut cabochon or carbuncle-shaped, and the lines (which are due to the fibres of asbestos) are kept in the centre of the stone, and play like the eye of a cat when the stone is moved.
The quartz cat’s-eye is easily distinguished from the oriental of chrysoberyl cat’s-eye, as it is softer and much lighter.
Crocidolite or tiger-eye is a light-brown, brownish-yellow to dark-green, and greenish-blue quartz, which has the same chatoyant qualities as the cat’s-eye. When cut cabochon, the crocidolite is called tiger-eye.
This beautiful mineral was very rare some years ago, and good specimens were sold by the carat.
Great quantities, however, have lately been found in South Africa, and although the finest pieces are still used for cameos and intaglios, many objects, such as paperweights, umbrella handles, match-safes, etc., are now cut from this stone.
Crocidolite is often artificially colored to very closely imitate some of the finest shades of the oriental cat’s-eye.
Heliotrope or blood-stone, as this variety is commonly called, is a dark-green quartz, translucent to opaque, and covered with small red spots or blood-colored blotches, from which the stone derives the name of blood-stone.
This stone has long been used for seal and signet purposes, and many fine intaglios and cameos carved in blood-stone are in existence.
Bucharia, Tartary, Siberia, East India, China, the island of Rum in the Hebrides, the United States, and Canada are some of the places where the heliotrope is found.
The chrysoprase is an apple-green chalcedony, sometimes olive- or whitish-green. It is translucent, scratches glass, and has the specific gravity of 2.56.
The color is due to the presence of oxide of nickel. This stone is found principally in Silesia, but also in Siberia and the United States.
Large pieces of chrysoprase are rare, and even the best specimens lose their color in course of time.
A translucent, spotted leek-green, green quartz, which loses its polish on exposure to the air, is known as prase.
This stone is found principally in the iron mines of Brietenbaum,Saxony, and also in Brittany, the Tyrol, Scotland, Salzburg, Finland, and the United States.
Prase is sometimes known commercially as “mother of emerald,” and a greenish crystalline quartz is also often called prase.
Plasma is a dark grass-green quartz, feebly translucent, and is sometimes covered with white or yellow spots. Plasma is somewhat lighter in weight than the heliotrope and does not take as fine a polish.
This stone is found in India, China, and in the Black Forest, Germany.
Chalcedony is cloudy or translucent, white, yellowish-gray, blackish-brown, light to dark-blue, milky-white, and black.
This quartz is sometimes nearly transparent, waxy in lustre, and in some varieties has a light gray and transparent base with dark cloudyspots. This last variety is called “cloudy chalcedony”. Another kind, with gray and white stripes alternating, is known as chalcedonyx.
Iceland, the Faroe Islands, Hüttenberg, Loben, Saxony, Hungary, Nubia, Nova Scotia, Oberstein, Ceylon, India, Siberia, Carinthia, the Hebrides, the United States, and Canada are places where chalcedony is found.
Agate is an improved variety of chalcedony and comprises the following kinds.
Banded or ribbon agate, running in delicate parallel layers.
Eye agate, forming concentric rings with a dark centre, giving the appearance of a human eye.
Fortification agate, running in circular parallel zigzag lines like the walls of a fortress.
Rainbow agate is a thin or concentric structure which when cut across and held towards the light shows an iridescence.
Moss agate, light-gray to white and translucent to opaque agates, display black tracings like fine moss or trees. Mocha or tree agates are covered with black, brown, or red figures, as of trees and plants.
Beckite or silicified coral shells, silicified wood, wood agate, wood opal, cloudy agate, and agate jasper are some of the many varieties of this class.
The common carnelians, blood-stones, and onyxes are usually counted among the agates.
Uruguay, Brazil, Oberstein, Silesia, Surinam, India, Arabia, Saxony, Scotland, the United States, and Canada are the principal places where agates are found.
Onyx is a variety of chalcedony in bands or strata of white, gray, and black, translucent to opaque, and generally found where agates abound.
The layers or bands are in even planes, and the colors, white andblack, white and brown, or brown, white, and black, alternate. This stone is largely used for cameos, the base being usually of black or brown, and the engraved or upper part white- or cream-colored.
When one or more layers are of carnelian or sard, the stone is called sard-onyx. Sard is a rich brown color inclining to red, and when held against the light shows a red hue.
Onyx and sard-onyx are often artificially improved by boiling the stones in honey, oil, or sugar water, and then in sulphuric acid. The acid carbonizes the sugar or oil which the stone has absorbed and gives it a deeper color.
For red, protosulphate of iron is added, and for a blue color to imitate lapis lazuli, yellow prussiate of potash is added to the protosulphate of iron.
Only the porous parts of the stones, usually the dark parts, absorb the sugar or oil, and so aid the contrast of the colored with the white layers.
Carnelian is a clear red translucent chalcedony, and is usually of a gray or grayish-red color. Several weeks of exposure to the sun’s rays and subsequent heating in earthen pots enhances and deepens the color.
The brownish-red or dark-brown carnelian is called sardoine or sard; the blood-red to pink varieties, with an upper layer of white onyx, are called carnelian onyx, and the stones with a brown or sard base and a white top are called sard-onyx.
Carnelians are sometimes of a yellowish-brown or yellow color, but red to brown are the principal colors.
The secret of coloring agates was discovered in the early part of this century, and about the same time agates became scarce in Oberstein, while large finds were made in Brazil and Uruguay, especially of agates with red layers. This variety comes chiefly from Brazil.
Besides Uruguay and Brazil, carnelian is found in Arabia and India. The most beautiful specimens of intaglios are engraved on sardoine, and some of the finest cameos extant are of sard and carnelian onyx.
Jasper is an impure opaque quartz, usually containing more iron than agate, and lacking the quality of translucency. Jasper occurs in red, brown, ochre-yellow, dark green, brownish-green, grayish-black, and grayish-blue; sometimes containing bands or spots or quartz formations, and often found with regular zones or bands of various colors.
Egyptian jasper or Egyptian pebbles are names given to varieties that are usually brown with inner bands of lighter hue, approaching cream in color, and sometimes having dark bands with spots or markings.
Egyptian jasper is found near Grand Cairo, and other varieties arefound in the Urals, Saxony, Devonshire, Nova Scotia, Canada, and the United States.
The specific gravity of jasper varies from 2.31 to 2.67; it scratches glass, but yields to rock-crystal.
False lapis is jasper or agate artificially colored blue to imitate the true lapis. Lapis lazuli is softer than false lapis, being only 5 to 5.5 in hardness.
Sappharine or siderite is a sapphire or sky-blue chalcedony occurring in Salzburg.
Nicolo is a variety of onyx with a black or brown base and a band or layer of bluish-white on top. The upper layer is not flat, but convex, and is always thicker than the lower one.
Hematite was once largely used to engrave upon, many of the ancientintaglios being on this mineral. It is now cut to simulate black pearls, and is also used in the cheaper jewelry, both engraved and cut cabochon.
Hematite has the hardness of 5.5 to 6.5, and specific gravity, 4.2 to 5.3; it is opaque, and shows a red streak when scratched. It is composed of:
The colors of hematite are dark-steel gray to iron-black, and sometimes brownish- to blood-red. The lustre is highly metallic, with slight iridescence.
The island of Elba, France, Switzerland, Italy, Norway, Sweden, Bohemia, England, Brazil, Chili, Canada, Spain, and the United States are places where hematite is found. The Germans call this mineral “blood-stone,” and it is also known as specular iron ore and iron glance.
Obsidian, or volcanic glass, does not occupy a high position as a gemor as an ornamental stone, but its antiquity and occasional use among the agates and semi-precious stones will justify its mention.
This mineral is a melted lava, and consists of silex, alumina, and a little potassa, soda, and oxide of iron. Obsidian is 6 to 7 in hardness, has a specific gravity of 2.25 to 2.8, is sometimes transparent but mostly translucent to opaque, and is vitreous to metallic in lustre. It is brittle and not easily attacked by acids. It melts before the blow-pipe and takes a high polish.
Obsidian comes from volcanoes, and is found in Iceland, Teneriffe, Lepare islands, Peru, Mexico, Sicily, and on all volcanoes. The color is velvety-black to gray, brown, greenish-black, yellow, blue, bottle-green, and white, seldom red, and often with black or yellow spots or veinings.
Iceland agate lava, volcanic lava, and royal agate are all obsidian.
Malachite although sometimes used for jewelry, is now more largelyemployed for mosaic work and ornamental vases, and is sufficiently costly and rare to be classed amongst the precious stones.
Malachite is 3.5 to 4 in hardness; has a specific gravity of 3.6 to 4; is translucent to opaque; the lustre is vitreous to adamantine. It is attacked by acids, and melts before the blow-pipe. It is composed of:
Malachite occurs in emerald or verdigris green color, sometimes in alternating stripes of different shades of green, and occasionally in leek- to blackish-green.
Malachite is found in Russia, France, the Tyrol, England, Scotland, Ireland, Germany, Africa, Chili, Australia, and the United States.
The finest specimens are found in the Urals—a block three and a half feet square, being valued at 525,000 roubles.
The making of jet or mourning jewelry was once a very large industry in France and England, and even now Whitby jet is well known in commerce.
Jet is a species of bituminous coal (cannel coal) which can be cut with a knife. The hardness is 1 to 2.5; specific gravity, 1.35; its lustre is not very high, and color pitch-black.
It is found in England, France, Hesse, Spain, Italy, and Prussia.
Amber is a fossil, and is not to be classed amongst minerals, but this material has always been used as an ornament, and a few notes will not be out of place here.
This vegetable fossil, which has been known to the world for ages, the Greeks called electron.
It is very light, having a specific gravity of 1.065 to 1.08, and is 2 to 2.5 in hardness.
The principal color is yellow, in various shades, sometimes running into white or reddish-brown and black.
Amber is transparent to translucent, possesses single refraction, a resinous lustre to a high degree, becomes electric by rubbing, and burns readily before the blow-pipe.
Amber when heated becomes soft and pliable.
Amber is composed of:
Amber is imitated by gum copal, and even the insect enclosures which occur in real amber are copied.
These imitations can be detected by placing the specimen in water or alcohol. This is also a good test for pieces of real amber that have been melted or glued together.
Amber is thrown up by the sea, in rivers near the sea, or on thesea-shore, and has been found in nearly all parts of the world.
The Russian, Baltic, and Sicilian coasts have yielded the larger portion of the production, but supplies come also from Galizia, the Urals, Poland, China, and the United States.
For ornamental purposes the faceted amber beads are largely used, but of late years these have been closely imitated in glass.
Coral, although not a precious stone, has been largely used in jewelry, and as some of this beautiful substance is very valuable, a few words will not come amiss.
Red or precious coral is the work of a family of zoöphytes which live mostly in cavities of rock in the sea.
These polyps build their homes at a depth of two to seven hundred feet under the surface of the sea, and although the single groups of coralare sometimes several feet long, the usual size is about twelve inches high, and about one inch at the thickest part of any single branch.
Coral is usually red, and rarely white or black, while the pale rose-pink is the most esteemed color.
Coral is mostly found at Calle, off the coast of Africa, but also on the coasts of Tunis, Algiers, Corsica, Barbary, Majorca, and Minorca.
Coral fishing-vessels leave Italy the beginning of March and return from the African coast in October; at one time as many as four hundred vessels were engaged in this industry.