Fig. 5.Fig. 6.
Fig. 5.Fig. 6.
These proportions do not refer to colored gems, which are cut thick or shallow to deepen or diminish the color of the stone. The step cut,fig. 7, now principally used for emeralds, can be advantageously used for other colored stones.
The crowned rose cut,fig. 8, is applied to small diamonds, andoccasionally to colored gems. This cut consists of twenty-four facets, and a well proportioned rose is one half of its diameter in thickness.
Fig. 7.Fig. 8.
Fig. 7.Fig. 8.
Fig. 9.Fig. 10.
Fig. 9.Fig. 10.
To the smaller and more common roses only twelve facets are given.
Besides the above-mentioned forms, there are the:
The last two beautiful forms of cutting are frequently given to fine paste or imitation diamonds.
Of late years nearly all gems have been cut quite round, and in many instances with a sacrifice of size and brilliancy.
The diamond is one of the most precious minerals, and yet it consists of pure carbon, the most common substance that is known, a substance that is present in all animal and vegetable bodies and in the larger number of minerals. When carbon is crystallized the result is the diamond, which is always found in detached crystals, either octahedrons or rhombic dodecahedrons, the planes of the angles being often convex or rounded,—this curving crystal being peculiar to the diamond.
The cleavage is perfect, and, parallel to the faces of the octahedron, the fracture is conchoidal or curved. The diamond is not acted upon byacids or alkalies, is infusible but combustible, and burns under heat of a very high temperature. Diamond powder burns readily, but larger pieces are not affected by the blow-pipe.
The diamond is a non-conductor of electricity, but acquires positive electricity when rubbed, and retains it for half an hour. After being exposed to the solar rays, the diamond presents a distinct phosphorescence in the dark. It possesses single refraction, but belongs to those bodies which reflect light most strongly, and its magnifying power is much greater than that of glass; it does not polarize light; its lustre is adamantine, and specific gravity 3.5 to 3.6. The diamond is the hardest of all known minerals, ranking No. 10 in Moh’s scale of hardness.
White, and the different shades from very light yellow to dark yellow or canary, comprise, according to the popular idea, the colors of the diamond. Yet the diamond is found in green, red, blue, brown, olive,orange, and black, and also in the various shadings of these colors and in opalescent tints.
As the limpid or white diamond surpasses all other white stones in the power of its lustre and the magnificence of its fire, so do the colored diamonds outrank the emerald, ruby, sapphire, and other gems of like colors.
Colored diamonds, excepting light yellow and brown, are rare, and hence are the most valuable of precious stones. The limpid or perfectly white and the white with a bluish tint are the most sought after, while fine deep golden yellow or canaries and pronounced fancy colors always find a ready market.
Diamonds come principally from the mines in South Africa; some are found in Brazil and India, and fewer in Sumatra, Borneo, the Ural Mountains, and Australia. Crystals have also been found in the United States.
The amorphous or carbon diamond is found only in Brazil. The pebbles ormasses are opaque, steel-gray to black in color, and sometimes weigh 1,000 carats.
This carbonate is principally used to point rock-drills and for other engineering purposes. The coarse variety of crystallized diamonds is called bort, and as this is unfitted for gem purposes because of imperfections, it is ground into powder and used for cutting and drilling precious stones.
White sapphires, white zircons, white topaz, and rock-crystal sometimes pass for diamonds. The first two are heavier, the topaz lacks brilliancy, and the crystal is lighter than the diamond.
It is also the case that these four stones, especially the crystal, are easily scratched by a diamond.
The best style of cutting for a diamond is the brilliant, of 66 facets, including the table and culet. The proper proportions of a well cut brilliant is ⅓ for the crown and ⅔ for the culet. The table and culet must also be in proportion to the size of the stone.
This many-colored mineral, composed of nearly pure alumina, produces gems which in some cases are more valuable even than diamonds. The ruby, sapphire, Oriental emerald, Oriental topaz, Oriental amethyst, Oriental aquamarine, Oriental chrysolite, Oriental hyacinth, star ruby, star sapphire, star topaz, and ruby and sapphire cat’s-eyes are all corundums of different colors. The ruby is a red sapphire, and the Oriental topaz a yellow sapphire, while the Oriental emerald is a green sapphire, etc., etc.
In hardness corundum ranks next to the diamond, ranking No. 9 in Moh’s scale.
The specific gravity is 3.9 to 4.1, the crystallization rhombohedral, and cleavage basal, the crystals breaking across the prism with nearly a flat surface.
In lustre, the corundum is vitreous, its refraction double but not to a high degree, and it is susceptible of electricity by friction, which the polished specimens especially retain for a considerable time.
Corundum is unaffected by chemicals, and is infusible alone, but in combination with a flux it melts with difficulty into a clear glass.
The chemical composition of precious corundum is:
Thus it will be seen that corundum is composed almost wholly of alumina,—one of the constituents of common clay, which, when colored by traces of metallic oxides, chrome, etc., produces a greater variety of precious stones of a high rank than any other mineral.
The red sapphire or ruby is the most valuable of the corundum family, and when found of a good color, pure and brilliant, and in sizes of one carat and larger, it is much more valuable than a fine diamond of the same size.
Fine rubies larger than 1½ to 2 carats are very rare, and when a fine stone from 3 to 5 carats is offered for sale, the price mounts into the thousands.
The color varies from the lightest rose tint to the deepest carmine; that color, however, which has the greatest value is known in commerce as pigeon’s blood, and is the color of arterial blood, or of the very centre of the red ray in the solar spectrum.
The imperfections in rubies, as in all corundums, consist largely of clouds, milky spots, and cracks. A perfect ruby is rarely met with, and a stone possessing brilliancy and the true color, even if slightly defective, is considered more valuable than an absolutely perfect ruby of an inferior color.
Rubies are found in Siam, Ceylon, Burmah, Brazil, Hindustan, Borneo, Sumatra, Australia, France, and Germany.
Where rubies and sapphires are met with it is said that gold is almost sure to be present.
Chemists have succeeded in producing minute crystals of rubies and sapphires which, under the microscope, presented the true crystallization of corundums, and upon being tested proved to be of the same hardness as rubies and sapphires; but these specimens were small, and cost very much more to produce than their commercial value.
Ruby spinels, garnets, hyacinths, red quartz, burnt Brazilian or rose topaz, and red tourmaline are sometimes passed off for the ruby.
The true ruby will scratch all of these stones readily, the spinel is lighter in specific gravity, and has generally a slight tinge of yellow, even in the most pronounced red specimens.
The ruby will turn green under the flames of a blow-pipe, but when cooled off, resumes its original color.
The garnet and topaz are easily scratched by the ruby, the hyacinth isheavier, and quartz and tourmaline lighter than the ruby. Some so-called reconstructed rubies, recently offered for sale, are of a very fine color, and closely resemble the Oriental gems.
The hardness and specific gravity are the same, but they differ in one very important point, namely: they lack the brilliancy of the true ruby. In addition to this lack of fire, a microscopical test discloses formations which will distinguish the manufactured from the natural stone.
The blue corundum, ranging in color from the lightest blue to deep blue and black, is the same stone as the ruby, the only difference being in the color.
The choicest color is the soft velvety blue, approaching the corn-flower in shade and exhibiting that color vividly by artificial as well as by natural light.
The deeper-colored stones are known as male, and the light-colored ones as female sapphires.
Although choice sapphires are rare, a much greater quantity of good and large stones are to be had than of rubies, and therefore the price of a large sapphire does not advance in the same proportion as the price of a large ruby.
The Oriental emerald or green sapphire does not approach the beryl or true emerald in depth of color, but because of its superior hardness and brilliancy, added to its extreme rarity, it is the most valuable of green gems. The Oriental amethyst or purple sapphire sometimes reflects a red color by artificial light, and is valued highly as a gem stone; the common amethyst is softer, less brilliant, and loses by artificial light.
The various other colored sapphires, such as yellow or Oriental topaz, light green or Oriental aquamarine, greenish-yellow or Oriental chrysolite, and aurora-red or Oriental hyacinth, are all valuable as gemstones when they are pure, well cut, and have pronounced colors—in fact, the name Oriental is given to distinguish the corundums from the less valuable minerals of the same colors which they resemble, but which they greatly surpass in beauty and value because of their brilliancy and superior hardness.
Asterias or star stones are corundums of three different colors; the star sapphire proper is a grayish blue, the star ruby red, and the star topaz yellow.
These stones are usually cut cabochon or convex, and display under the rays of the sun, or when exposed to one candle or other artificial light, a beautiful star with six points.
This star is produced by foreign substances in the corundum, and the lapidary brings about the regular effect by cutting a pointed carbuncle so that the centre of the star begins at the apex, and the six brightstripes radiate to the base of the stone.
The bright lines of the star following the light move over the surface of the stone and produce a remarkable effect. These stones are amongst the most wonderful of mineral productions, and good specimens are very valuable.
The corundum cat’s-eye, called Oriental girasol or sunstone, has a bluish, reddish, or yellowish reflection of light of a lighter shade than the stone itself, and which moves on the convex surface of the stone like the lines of a star stone.
It is only during the past century that mineralogists make a distinction between the minerals spinel and corundum.
The composition of the spinel was discovered towards the end of the last century, and was found to be about seventy per cent. alumina, twenty-five per cent. magnesia, and small parts of oxide of chrome, silica, and protoxide of iron.
Up to that time, red spinels had always been confounded with rubies, and many celebrated so-called rubies have been shown to be spinels by modern mineralogists.
This beautiful mineral is found in many colors, from pink to rose-red, carmine, cochineal, blood-red, hyacinth, pale to dark blue, violet and indigo blue, grass-green to blackish green, and sometimes colorless. There is also a black variety called pleonaste or ceylonite. Spinels crystallize in octahedrons and their modifications, the fracture is conchoidal, specific gravity 3.5 to 3.6, and hardness No. 8 in Moh’s scale; only the diamond, corundum and chrysoberyl will scratch the spinel.
Its refraction is single, the lustre highly vitreous, and it does not easily acquire electricity.
Acids do not attack the spinel, nor has the blow-pipe any effect on this mineral, except to change the red to a brownish or colorless state, but the original color returns when the stone cools.
Flawed or imperfect stones are liable to crack or split if heated too much. With borax or salt of phosphorus the spinel melts into a colorless or green-tinted glass.
Spinels are found in clay and in the sands of rivers, in East India, Hindustan, the province of Mysore, Farther India, Pegu, Ceylon, North America, Sweden, Bohemia, and Australia.
The red spinel, and especially those tints which approach the red corundum or true ruby in color, are the most valuable, and are known as ruby spinels.
Very fine specimens of ruby spinels of one carat and larger are quite rare and command good prices.
Rose-colored spinels are known as balas-rubies, pale-blue spinels as sapphirines, and the hyacinth-red, yellowish-red, and orange-yellow spinels are called rubicelles.
All these different-colored spinels, if pure and of great brilliancy,are valuable as gem stones, being only surpassed in hardness and brilliancy by the diamond and corundums.
The white spinel, which is seldom found, is sometimes confounded with the diamond, having the same specific gravity and single refraction, but as it lacks the fire and is easily scratched by the diamond, the danger of mistaking one for the other is slight. Burnt amethyst, which often resembles the spinel, is lighter and softer, while burnt topaz, although it is identical with the spinel in hardness, is somewhat lighter and possesses remarkable electric powers, becoming electric by either rubbing, heating, or pressure, and retaining electricity for upwards of twenty-four hours.
The zircon is easily distinguished from the spinel because of its much greater specific gravity. It is also doubly refractive and softer.
Garnets are softer, lack the play of color and brilliancy, and fuse easily into a light-brown or black glass.
The beryl is a mineral belonging to the primitive formation, and is found in quartz veins and granite.
It crystallizes in six-sided prisms and is composed largely of silica, the third most common of earth’s productions. The beryl is 7.5 to 8 in hardness, scratching quartz, but is scratched by topaz.
The specific gravity is 2.67 to 2.73, making it one of the light minerals. Its lustre is vitreous and refraction double to a slight degree; its cleavage is imperfectly basal, and it becomes electric by rubbing.
Acids do not attack the beryl, but it melts with borax and is soluble in salts of phosphorus.
This stone is found in various colors, grass-green, pale-green, light-blue, greenish-blue, greenish-yellow, yellow, and sometimes pink.
The most important of these colors is the grass-green, which forms aseparate division of the beryl family, and is known as the emerald.
The emerald or green beryl is one of the most highly prized of the gem stones. Its magnificent color has rightly been compared to the color of the fresh grass in spring, and in brilliancy this stone far exceeds all other green gems, excepting only the very rare green corundum or green sapphire.
The emerald is said to be very soft when first withdrawn from the mine, but it hardens by exposure to the air.
A perfect emerald of fair size is a rarity, so that the saying “an emerald without a flaw” has passed into a proverb.
This stone is so light, compared to a diamond or sapphire, that a carat emerald will be very much larger than either of the above stones.
The emerald is composed of:
The vivid green color of the emerald is supposed to come from the oxide of chrome, as the other beryls do not contain chrome.
Emeralds are found in New Granada, near Bogota, Egypt, East India, Burmah, Ural in Europe; Salzburg, Austria; Mt. Remarkable, South Australia; and North America. Some of the finest come from the mines of Muza, near Bogota, and the best stones are called Peruvian emeralds. During the conquest of Peru by the Spaniards, many very fine emeralds were destroyed by the invaders, who tested them by grinding and pounding, and concluded that the emeralds were worthless, because they were not as hard as the diamonds or sapphires.
In 1587, Joseph D’Acosta returned to Spain with two cases of emeralds, each case weighing one hundred pounds.
Green tourmaline sometimes passes for the emerald, but it is somewhat softer and considerably heavier.
Olivines or chrysolites, if of a fine green color, sometimes resemble the emerald, but they are much heavier than the emerald and have a fatty lustre. Green spinels are heavier and harder than emeralds.
The second and less valuable division of the beryl family comprises the following colors:
Clear light sky-blue, called by lapidaries aquamarine; very light greenish-blue, known as Siberian aquamarine; and a greenish-yellow variety, called aquamarine chrysolite.
These three kinds are usually very brilliant, and especially so by artificial light, in which respect the beryl is superior to many of themore valuable gem stones. Beryls of very large size have been found in New Hampshire, one of which has been estimated to weigh over two tons. While the large specimens are worthless for gem stones, some very handsome aquamarines and golden-yellow beryls have been found during the past few years in New Hampshire and Connecticut. These stones, when cut, compare favorably with the best of their kind.
The name chrysoberyl is derived from two Greek words signifying golden-beryl. This name is well suited to the golden-yellow variety, but the chrysoberyl also includes many other colors: such as green, greenish-yellow, brownish-yellow, white, and dark-brown to black.
Three varieties of chrysoberyls are known as cat’s-eyes, cymophanes, and alexandrites.
The chrysoberyl crystallizes in the trimetric or rhombic system; the cleavage is imperfect; fracture conchoidal; hardness, 8.5, being the third hardest stone; specific gravity, 3.65 to 3.8; and lustre vitreous to greasy.
The composition of the chrysoberyl is: alumina, 80.2; glucina, 19.8; with traces of protoxide of iron and oxides of lead and copper. The chrysoberyl is doubly refractive to a high degree, acquires positive electricity lasting several hours, is infusible alone, but melts with borax or salts of phosphorus to a clear glass, though with difficulty.
The chrysoberyl is unaffected by acids, but with a solution of cobalt nitrate the powdered mineral becomes blue.
Transparent greenish-yellow chrysoberyls are sometimes called Oriental chrysolites. These, and the brownish-yellow stones are the gems most used in jewelry.
The chrysoberyl cat’s-eye, or Ceylon cat’s-eye, is found in variousshadings of yellow, brown, and green, and sometimes nearly black. These stones are translucent to opaque, and have a bright band of light running through the centre. This band is nearly always white, and in fine specimens is sharply defined, not too wide, and is in the centre of the stone.
The cat’s-eye chrysoberyls are always cut convex or cabochon shape, and as the stone is moved from side to side the band of light moves over its surface.
The cymophane, or floating light, as the name denotes, is a chrysoberyl with a bright spot of light which seems to float over the surface as the stone is moved. The cymophane is also cut cabochon.
On the day that the Emperor Alexander of Russia attained his majoritythe Ural chrysoberyl, of a dark-green color, was found in the emerald mines of Takowaja in the Catherine Mountains.
This wonderful stone is emerald-green to dark-green in color, with often a slight red tint, but by artificial light the green of good specimens changes to a beautiful columbine-red.
As the colors green and red are the national colors of Russia, and the date of discovery of this stone in Russia occurred on the Emperor’s birthday, the name alexandrite was given to this species of chrysoberyl.
The alexandrite is found in large pieces, but is nearly always flawed and cracked. This is a much-sought-after gem stone, and specimens of from one to five carats command good prices. Up to the present time, however, good alexandrites have been rare, and the demand has always exceeded the supply.
Cat’s-eyes and cymophanes are found in Brazil in alluvial deposits of rivers, and consequently in rolled and rubbed masses.
Chrysoberyls are also found in Russia, Germany, America, Borneo, Pegu, and Moravia.
Chrysolites and topazes are sometimes passed off for chrysoberyls. The chrysolite is, however, lighter and softer, while the topaz becomes electric from heating, and is softer.
Quartz cat’s-eyes, which are mistaken for chrysoberyl or Oriental cat’s-eyes, have a specific gravity of about 2.65, hardness of 6 to 6.5, and are soluble in fluoric acid, besides melting with soda into a clear glass.
They lack the bright, hard polish of the chrysoberyl cat’s-eye, and there should be no difficulty in discovering the difference between the gem and the inferior stone.
The zircon, hyacinth, jacinth, or jargoon belong to the tetragonalsystem of crystallization. The cleavage is imperfect, fracture conchoidal, and specific gravity 4.4 to 4.7, the stone being much heavier than any other gems. Its hardness is 7.5 and lustre vitreous to adamantine, and refraction double to a high degree.
The zircon is phosphorescent when heated; before the blow-pipe it is infusible, but loses its color; and with borax it melts into a transparent glass. Sulphuric acid affects this gem after long maceration.
The composition of the zircon is: zirconia, 66.3; silica, 33.7; with a trace of peroxide of iron.
Under the microscope, the texture of these gems presents a watery appearance, called by the Frenchratiné, and which looks like a liqueur poured into water. This is a strong distinguishing point in the zircon.
The zircon, hyacinth, jargoon, and jacinth are the same gems but of different colors.
The brown, violet, and green colors are known as zircons, the red ashyacinth, the yellow as jacinth, and the grayish-white and white as jargoons.
The jargoon has often been palmed off as a diamond because of its transparent color and adamantine lustre.
The zircon is found in Ceylon, Germany, France, Bohemia, America, and in fact in nearly all parts of the earth, as many as 120 localities having been noted where specimens of the mineral have been discovered.
The zircon can be distinguished from the garnet by its peculiar diamond-like brilliancy and its specific gravity.
The turquois is never found in crystals, but in reniform or stalactitic masses. The color varies from pea- and apple-green to greenish-blue, sky-blue and dark-blue.
The hardness of the turquois is 6., specific gravity 2.6 to 2.8, lustre waxy, and condition opaque to slightly translucent.
Before the reducing flame of the blow-pipe, the turquois does not melt, but becomes brown and colors the flame green. With borax and salts of phosphorus the turquois melts to a clear glass, while it is also soluble in hydrochloric acid. Oriental or mineral turquois is composed of:
The best color is a clear deep sky-blue, and in the true turquois this color improves by artificial light; imitation turquoises, however, lose their fine color under the same conditions.
The finest gem turquoises come from the northeastern part of Persia, between Nishapoor and Meshed. Here they are mined and partly cut, andthen the Persian merchants carry them to Russia, where they are sold at the great annual fair of Nijni-Novgorod and in Moscow. Mineral turquoises are also found in New Mexico, Arizona, and Nevada, but not of sufficient size or sufficiently good color to make gem stones, although they are prized for collections. Specimens are also found in Burmah, Khorassan, Thibet, China, Silesia, Saxony, and on the Isthmus of Suez. The stones from these places have, as a rule, but little value, as the color fades or turns green from exposure to the light. Of late however, some very good turquoises have come from Egypt. The color of a faded Persian turquois can sometimes be restored by simply repolishing the stone.
Occidental or bone turquoises called new rock or odontolites, to distinguish them from the Persian or old rock stones, are of organic origin.
They are cut from the teeth of mammoths, mastodons, dinotheriums, etc., and are found near the town of Simor, in Lower Languedoc, France.
These teeth, the enamel of which is nearly as hard as the mineral turquois, are colored by contact with phosphate of iron and copper, which gives them a dark-blue, light-blue, and bluish-green color. They are easily attacked by a file, and totally destroyed by aqua-fortis.
When heated, the fossil turquois or odontolite gives an offensive odor, owing to the decomposition of animal matter.
The odontolite is lighter than the mineral turquois, changes color by artificial light, loses color in distilled water and alcohol, and is translucent on the edges.
This fossil turquois does not fade like the mineral turquois, but by artificial light appears of a dirty grayish-blue.
Turquoises are sometimes artificially stained, but this can be detected by applying a drop of ammonia to the back of the stone, and if the color is artificial the ammonia will eat it off, leaving a green spot. Ammonia does not affect the color of the Persian turquois. The so-called“reconstructed” turquoises are very close imitations of the real, but are easily distinguished, as they change rapidly to a deeper blue when immersed in water, and while wet the surface of the stone shows cracks in every direction. These stones become softer through soaking in water or alcohol. The original color, however, returns when the stone is dry, but the cracks remain in faint outline.
The tourmaline or precious schorl is known under many different names, and no other mineral has such a suite of colors.
The colorless variety is known as achroite; the red, as rubellite or siberite; the blue, indicolite or Brazilian sapphire; the green, Brazilian emerald; and the yellowish-green, Ceylon chrysolite or Ceylon peridot. Besides the above colors and their shadings, the tourmaline occurs in black and brown.
The crystallization is obtuse rhomboid, and generally forms six-, nine-, and twelve-sided prisms.
Some of the crystals are very large, specimens over eight inches long having been mined.
The tourmaline crystals are remarkable for their varied and beautiful groupings of colors. Some are internally blue or brown, surrounded by a bright carmine red or dull yellow; others are red internally and are enveloped by a green exterior; crystals are sometimes pink at the summit and light green at the base, or crimson tipped with black, or white at one end shading into green and finally into red at the other end. The hardness of the tourmaline is 7 to 7.5, specific gravity 3 to 3.1, and lustre vitreous.
The tourmaline becomes decidedly electric by heating or rubbing, and will readily attract small pieces of paper and other small objects. The rubellite or red tourmaline is composed of:
The green tourmaline is composed of
The tourmaline possesses double refraction to a high degree, and its power of polarizing light is so great that, cut into slices, it is used in the polariscope for analyzing other minerals.
If two slices of tourmaline, cut parallel to their axis, be laid one on the other in one direction, both are transparent; if laid in another direction they become opaque, and if a doubly refracting crystal beplaced between the two plates of tourmaline, the part covered by the crystal is transparent while the other is opaque.
Tourmaline melts with borax into a transparent glass; the rubellite turns white, and the indicolite and green tourmalines turn black, under the blow-pipe.
Tourmalines can be distinguished from other gems by their specific gravity, but principally by their property of assuming polaric electricity after being heated, one end becoming positive and the other negative.
The history of the discovery of the tourmaline and its electric property is a curious one.
On a warm summer day, early in the eighteenth century, some children were playing in a courtyard in Amsterdam. Amongst their playthings were some precious stones which the Dutch navigators had brought from Ceylon. Some of the stones seemed to be possessed of the strange power of attracting and repelling small bits of straw, ashes, and other lightsubstances. The little ones called their parents to witness this strange phenomenon, and the stolid Dutch lapidaries, themselves puzzled at the sight, called the stonesaschentreckersor ash-drawers.
A number of years afterwards, careful experiments disclosed the wonderful electric powers of the aschentreckers or tourmalines. Purple, green, and blue tourmalines are found in Brazil. In Ceylon the stones are found in gravel beds. Rubellites or siberites are found in Siberia.
Tourmalines are also found in Moravia, the island of Elba, Sweden, Burmah, Tyrol, Canada, and the United States.
The first tourmaline deposits known in the United States were discovered at Paris, Maine, in 1820. Another wonderful deposit was found at Mt. Apatite in Maine in 1882, and up to the present time the finest tourmaline crystals have been discovered in the United States.
Really fine specimens of red, blue, or green tourmalines are uncommon and command very good prices.
The precious or noble opal, fire opal, common opal, hydrophane, and cachelong are different varieties of a mineral that is composed of about nine parts silica and one part water.
The colors vary from chalky-white to bluish-white, from yellow to red, and from a slight play of colors to the beautiful mingling of green, blue, and red with the most remarkable kaleidoscopic effects.
The opal is 5.5 to 6 in hardness, specific gravity 2 to 2.1, lustre glassy, and translucent from a slight to a very high degree.
The opal is found in an amorphous state and never crystallizes; in fact from the condition of the pockets in which this mineral is found, the indications are that the substance was once a fluid.
Under the blow-pipe the opal loses its translucency and cracks but does not melt. Sulphuric acid will cause it to turn black, and in a cold solution of caustic potash the opal is almost entirely soluble.
The precious or noble opal is found chiefly in the mines of Czernowitza, between Kaschau and Eperies, in Hungary, and in Gracias á Dios, a province in Honduras.
In olden times, the Greek and Turkish merchants carried opals from Hungary to the Orient, and then they were shipped to Holland and sold in Europe as Oriental opals.
The fire opal is of a yellowish-red color, and is found chiefly in Mexico, although it also occurs in Hungary, the Faroe Islands, Honduras, and Guatemala.
The common opal is found in Ireland, Denmark, Frankfurt, Guatemala, and South Australia, and also in Hungary and Mexico. These opals are translucent without fire or reflection.
The hydrophane is an opal that has lost color and brilliancy by reason of the evaporation of its water. If placed in water or alcohol, this stone becomes transparent, only to lose this quality when the water or alcohol has evaporated.
The hydrophane becomes transparent more quickly in warm than in cold water, but most rapidly in alcohol. If boiled in oil, the hydrophane is said to retain its brilliancy for years.
The cachelong is milky-white, and nearly opaque, and is found in small masses in the river Cach, in Bucharia, and also in Iceland.
Although one of the most magnificent of the gem stones, the opal for many years was under the ban of superstition. Now, this splendid stone once more commands a foremost place in the jewelers’ art, and the opal mines of Hungary and Queensland are being worked to their fullest extent to supply the demand.
Although an organic product, the pearl is always ranked amongst the most precious of gems, and is distinguished by being the only gem that does not require the lapidary’s touch to bring out its beauties.
Ancient writers have accounted for the origin of pearls by saying that they were formed of angels’ tears, or drops of dew from heaven, which, during the midsummer nights, fell into the gaping mouths of the pearl-oysters.
According to modern scientific investigation, the formation of the pearl does not seem to be the result of healthy natural causes, but comes from the efforts of the oyster to rid itself of some foreign substance, like a grain of sand, a bit of shell or vegetation, or some unwelcome visitor in the shape of a small water insect.
When annoyed by an intruding substance, the oyster begins to deposit its nacre, or mother-of-pearl, in regular concentric layers around the intruder, these layers gradually increasing in circumference and forming the pearl. Thus, like an onion, the pearl is merely a succession of layers or skins, starting from a small core, or nucleus, which is always present, though often only of microscopical size.
Pearls have sometimes been found where the outer layer, or skin, as it is technically called, has been discolored or otherwise injured, and when this top skin has been carefully removed the result was a somewhat smaller but perfect pearl.
This, however, is a very delicate operation, and at the pearling grounds is only resorted to by men of experience. The composition of the pearl is carbonate of lime, with a small proportion of organic matter, and the specific gravity 2.5 to 2.7.
The pearl is affected by acids, and is easily calcined on exposure to heat.
In color, the pure white, slightly transparent, is the most highly prized; while in India and China the bright yellow colors are sought after.
Decided colors, however, such as black, pink, and golden-yellow bring a high price, and, in fact, black pearls, if perfect in color and shape, are at present more valuable than any other kind.
The beauty and value of a pearl depend on form, quality of texture or skin, color, transparency or water, and lustre or orient.
In form, the perfectly round shape comes first in value, then a finely formed drop or pear shape, and lastly the oval or egg shape.
Pearls that are flat on one side and rounded on the other are called boutons or button pearls. These are frequently found attached to the shell, and are cut out and the bottom part smoothed and polished.
It is easy, however, to detect this class of pearls by the lack of pearly lustre on the side that was attached to the shell.
When a pearl is rough and odd-shaped it is called a baroque, and some extremely fantastic shapes are found, especially in fresh-water oysters.
The texture or skin of a fine pearl should be perfectly smooth and free from all spots, indentations, wrinkles, or scratches.
Pure white is the desirable color for a gem pearl, but many others that are slightly tinted with blue, pink, or yellow will pass for gems if they are otherwise perfect.
The transparency or “water” of a pearl, while not existing in fact, is still one of the requisites of a fine pearl; there must be an appearance of transparency, which adds to the beauty of the gem.
To describe the lustre or orient of the pearl, the author can only use the term pearly, as there is no other substance that approaches the brilliancy and color of a pearl, excepting, of course, mother-of-pearl—the nacre in the pearl-oyster.
Without orient or lustre, the pearl of finest form and color has but little value.
Lustre is to the pearl what brilliancy is to the diamond; when the orient is absent there is no life, no beauty.
Pearls are principally supplied by two groups of pearl-oysters ormussels: the marine or meleagrina margaritifera, a round-cornered square shell with very thick sides, measuring six to eight inches in length.
The color of this shell is mostly blackish-green, but it is also sometimes yellowish; the edges of the inner part of the shell are black, but the rest of the interior is the beautiful mother-of-pearl.
The oyster itself is small for the size of the shell.
This specimen is found on the coast of Ceylon, Persian Gulf, Japanese, Mexican and California coasts, the western shores of South America, Brazil, West Indian Islands, Panama, Sooloo Archipelago, and the northeast and northwestern coast of Australia.
The fresh-water or unio margaritifera is an even, egg-shaped mussel found in brooks, rivers, and lakes in temperate zones in nearly all parts of the world.
Some fine river pearls have been found in the United States, but mostof the American pearls are of a button or elongated shape, or are baroques or fancy-shaped.
In China many people engage in the business of making small pellets of clay or metal images, which in the month of May are introduced into the river mussels (mytilus cygneus).
The mussels are replanted, and in November they are taken up again. Some of the oysters die, but most of them are found to have been actively at work covering the little pellets or metal figures with nacre, and while no strictly first-class pearls are formed in this way, many curious little pearl figures or gods are made and sold to the curious or devout.
Pink or conch pearls are found in the Gulf of California and coasts of Mexico, Bahama Islands, West Indian Islands, and in some rivers in South America.
They seldom occur in regular shapes, and although they are termed pink pearls, they range in color from red to pale yellow, and are often found of a china-white color.
The pink pearl displays a wavy appearance and a peculiar sheen, something like watered silk. As the pink pearl is seldom found perfectly round and of a good color, such a specimen is very valuable.
The chrysolite, peridot, and olivine differ in color, but are practically of the same composition.
The chrysolite proper is of a pale greenish-yellow color, the peridot a deep olive-green, and the olivine of a yellowish or light olive-green color; these stones also shade into brown. They crystallize on the rhombic system, are transparent to translucent, 6.5 to 7. in the scale of hardness, and 3.3 to 3.5 in specific gravity.
The cleavage is distinct, fracture conchoidal, refraction double, and lustre vitreous, and in the olivines somewhat greasy.
These stones are easily affected by sulphuric acid, but are infusiblebefore the blow-pipe, excepting some kinds containing much iron.
With borax, they melt to a pale-green transparent glass.
Chrysolites are composed of silica, magnesia, and oxide of iron.
Perfectly crystallized chrysolites are brought from Constantinople, but the exact locality where they are found is unknown.
Less distinct specimens occur at Vesuvius, Mexico, the isle of Bourbon, Auvergne, Egypt, Natolia, Brazil, Germany, Pegu, Ceylon, Switzerland, and North America.
Peridots are distinguished by being the only precious stones that have literally dropped from heaven, as they have been found in meteorites.
The Oriental chrysolite of commerce is true chrysoberyl, and is harder and heavier than chrysolite, and the stone called Ceylon chrysolite isa greenish-yellow tourmaline, which is easily distinguished, as it is also harder while considerably lighter than the chrysolite.
The green garnet is of a pronounced green color, and is harder and heavier than the olivine or chrysolite. Although suitable for mounting in brooches and other ornaments, these stones are not sufficiently hard for the rough usage as ring-stones.
Almandine, almandite, Syrian garnet, essonite, cinnamon-stone, pyrope, Bohemian garnet, vermeille, Cape garnet, Cape ruby, Arizona ruby, American ruby, carbuncle, uwarowite, demantoide, grossularite, and Bobrowska garnet are some of the scientific and commercial names for different species and colors of the garnet group.
The crystallization of the garnet is isometric, refraction single, specific gravity 3.15 to 4.3, hardness 5 to 8, lustre vitreous,fracture uneven, colors red, violet, brown, yellow, green, and white, and the various shadings of these colors.
Most varieties fuse easily to a brown or black glass; the uwarowite fuses with borax to a clear chrome-green glass.
Syrian, almandine, almandite, and carbuncle are different names for the iron-alumina garnet.
In colors, these stones shade from deep-red to violet and brownish-red, and are composed of:
The specific gravity is 4. to 4.2, and hardness 7.5.
This garnet, sometimes called the precious garnet, is found in Ceylon, Pegu, Brazil, Greenland, Hindustan, Bohemia, Tyrol, Œtzthal, Carinthia, Styria, Switzerland, Ariolo, Canaria, Maggia, Hungary, Sweden, Norway, Scotland, Spain, and the United States.
Grossularite, or lime-alumina garnet, is known in commerce as essonite, or cinnamon-stone. The color is yellow, of various shades; specific gravity 3.5 to 3.65, and hardness 6.5.
These stones are sometimes sold for jacinths, but they are softer than the jacinth, and melt easily before the blow-pipe. Essonites come principally from Ceylon, but are also found in other places.
Pyrope or Bohemian garnet is the magnesia-alumina variety, and is of a uniform dark blood-red color. This stone is found in Bohemia, and although quantities of small pieces are found, large specimens are rare, and a piece that will cut into a four- or five-carat stone is seldom met with and commands a high price.
These garnets are found at Stiefelburg by Meronitz, Triblitz, Podsedlitz, and Neupaka.
The pyrope turns black under the blow-pipe, then red again, and meltswith difficulty into a black glass. With borax it melts to an emerald-green glass. The specific gravity of this garnet is 3.69 to 3.78, and hardness 7.5.
Vermeille is a name given to the orange-red almandine, Cape garnet to the bright red-yellow variety, Cape ruby to the pyrope, and American ruby to the blood-red kind found in New Mexico, Montana, and Arizona. Carbuncle is a term appliedto allgarnets cut with a smooth rounding top, sometimes called, after the French, cabochon.
Uwarowite or lime-chrome garnet is one of the rarest and most beautiful of the garnet group.
The color of this stone is emerald-green, hardness 7.5, and specific gravity 3.41 to 3.52. Uwarowites are found near Bissersk in the Urals of Russia, but rarely in specimens of sufficient size to cut into gems.
This garnet is heavier and harder than the true emerald.
Demantoide or Bobrowska garnet is a soft garnet, olive-green to brownand blackish-green in color, sometimes light green. It is found in the Bobrowska River in the Urals. The specific gravity is 3.85, and hardness about 6, its softness making it undesirable for many ornaments. Before the blow-pipe it fuses into a black bead.
These garnets are often sold as olivines; they are heavier than olivines and softer.
Demantoide is composed of:
Topaz belongs to the rhombic system of crystallization. Its cleavage is basal and perfect, fracture uneven, hardness 8, scratching quartz distinctly, specific gravity 3.4 to 3.6, lustre vitreous, refraction double, and colors ranging from colorless or white to bluish-white, light blue, wine-yellow, straw-yellow, golden-yellow, greenish- and pale-red to pink.
Topaz becomes electric from rubbing or pressure, and retains electricity for twenty-four hours. Before the blow-pipe topaz partly loses color, but does not melt, and with borax it fuses slowly to a white bead.
Topaz is partially attacked by sulphuric acid, and dissolves in salts of phosphorus.
The composition of topaz is:
Goutte d’eau or colorless topaz, sometimes called “slaves diamond,” Siberian or bluish-white, Brazilian or golden to reddish-yellow, Saxony or pale-wine yellow, Brazilian ruby or pink, Brazilian sapphire or light blue, and aquamarine or greenish, are the various commercial names for topaz.
Most of the Brazilian rubies or pink topazes are produced by heating the reddish or dark-yellow variety, either in a crucible or byenveloping the stone in German tinder and setting fire to the tinder. If heated too much, the stone is apt to become colorless, and if suddenly cooled it may crack.
Colorless or white topaz takes a very high polish, and is wonderfully clear and transparent.
The great Portuguese diamond, “The Braganza,” of about 1,680 carats, is supposed to be a white topaz.
Topaz is found in the Urals, Kamschatka, Alabaschka, Miask, Nestschinsk, Adun Tschilon, Villa Rica, Boa Vista, Capao, Lana, Minas Novas, Cairngorm Mts., Schlackenwald, Zinnwald, Schneckenstein, Ehrenfriedensdorf, Altenburg, Orenburg, Mourne Mts.—Ireland, Australia, New South Wales, Ceylon, Mexico, and the United States. False topaz, or the ordinary topaz of commerce, is yellow quartz resembling yellow topaz, but lacking its brilliancy and hardness; it is also very much lighter, being only 2.5 to 2.7 in specific gravity.
Beryl and chrysolite are often mistaken for topaz, but as they are softer and beryl is much lighter, they are easily distinguished from the topaz. The strong electric property of the topaz is also a conclusive test.
Oriental topaz, or yellow corundum, is harder and heavier than the occidental or true topaz.
Apatite, which is seldom used as a gem stone, sometimes resembles the beryl and emerald, but is much softer and rarely has the color and brightness combined of the former gems.
This mineral, composed principally of subsesquiphosphate of lime, is 4.5 to 5. in hardness, has the specific gravity of 2.95 to 3.25, is transparent to opaque, vitreous in lustre, infusible before the blow-pipe, and dissolves slowly in nitric acid. In colors, apatitevaries from colorless to sea-green, bluish-green, violet-blue, gray, yellow, red, and brown.
Apatite is found in Saxony, the Hartz Mts., Bohemia, Norway, Bavaria, England, St. Gothard in Switzerland, and in the United States.
Four varieties of felspar are used as gem stones—moonstone or orthoclase, sunstone or avanturine felspar, Amazon stone or green felspar, and Labrador or Labrador spar.
This variety of felspar is called orthoclase, adularia, and orthose, besides the commercial names of fish-eye, Ceylon or water opal, and in the yellow and red tints sunstone. Moonstone occurs in crystals and crystalline fragments, also massive and granular; its hardness is 6. to 6.5, specific gravity 2.4 to 2.6, refraction double, is not attacked by acids, and is composed of:
This beautiful stone is the clearest of all varieties of felspar. It is colorless, or only slightly tinted with blue, green, yellow, and flesh-red, and is transparent to translucent.
The lustre is vitreous, and a brilliant pearly streak of white light plays from side to side.
The yellowish- and reddish-tinted specimens are called sunstones, and are quite rare. These sunstones must not be confounded with the avanturine or felspar sunstone.
Moonstones are found principally in Ceylon and on the St. Gothard in Switzerland, but also occur in Bavaria, Greenland, Tyrol, Dauphine, Norway, and the United States.
During the past few years, large quantities of moonstone balls, cutlike whole pearls, have been used for jewelry—the stones being much sought as well because of their beauty as on the ground of the popular superstition that they will bring good luck to the wearer.
Small pieces or balls are not very valuable, but large perfect specimens command a good price.