Part 2

The mineral is either held by a pair of platina-pointed forceps, or powdered and placed on a metal plate or in a glass tube.

Before the blow-pipe, some minerals change color, but do not melt, while others retain their color, or swell up, or break into small particles, or melt into colorless or colored glasses.

The following is the scale of minerals used to test the different degrees of fusibility:

1. Gray Antimony. Fusible in coarse splinters in summit of candle flame without the blow-pipe.

2. Natrolite. Fusible in fine splinters in the summit of a candle flame without the blow-pipe.

3. Almandite. Does not fuse in candle flame; fuses easily before the blow-pipe in obtuse pieces.

4. Green Actinolite. Fusible before the blow-pipe in coarse splinters.

5. Orthoclase. Fusible before the blow-pipe in fine splinters.

6. Bronzite. Before the blow-pipe becomes rounded only on the sharp edges.

MAGNETISM.

There are but few precious stones that possess the power to act on the magnetic needle; among them are the chrysolite, cinnamon stone, almandine, pyrope, and garnet.

TRANSPARENCY.

Precious stones are, on the basis of their relative transparency, divided into four classes, as follows: _Transparent_, or admitting light freely and clearly; defining objects when used as a lens. _Semi-transparent_, admitting light, but only partially defining objects. _Translucent_, admitting light faintly. _Opaque_, not admitting light.

The more valuable precious stones, excepting opals and turquoises, are generally transparent.

PHOSPHORESCENCE.

Some precious stones display a distinct phosphorescence after exposure to the sunlight, and also upon the application of artificial heat, and through mechanical and electrical means.

Many diamonds, when taken to a dark room, appear quite luminous; this is also true of topaz, fluor spar, and other minerals.

ELECTRICITY.

Minerals acquire electricity through friction or heating, and in this state readily attract or repel small bits of paper and other light substances.

All minerals are electric, some displaying positive and others negative electricity.

The electric test of a precious stone refers to the length of time that a stone will retain electricity after friction or heating.

Some stones lose this quality in a few minutes, while others retain it a long time. The tourmaline is noted for its electrical properties, while the Brazilian topaz rendered electric by heating or rubbing has been known to affect the electric needle after 32 hours.

CUTTING AND POLISHING.

Although a finely developed diamond, ruby, or other crystal is sometimes found and used for jewelry, the beauty of a precious stone generally remains hidden within a rough and unsightly exterior until the lapidary’s art reveals the gem.

According to well known rules, there is one kind of cutting or faceting for the diamond or colorless gems and another for colored gems.

The brilliant cut, figs. 5 and 6, consists of an arrangement of fifty-six facets, exclusive of the table and culet. This cut is sometimes improved by the addition of eight star facets around the culet, which brings the number of facets up to sixty-four.

The following are the proportions of a well cut diamond or colorless gem:

⅓ above the girdle, fig. 6, A. ⅔ below " " " 6, B. The table 2/5 of the breadth of the stone, fig. 6, C. The culet ⅙ of the size of the table, fig. 6, D.

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, and occasionally to colored gems. This cut consists of twenty-four facets, and a well proportioned rose is one half of its diameter in thickness.

To the smaller and more common roses only twelve facets are given.

Besides the above-mentioned forms, there are the:

Huitpan, or single cut. 16 facet " double " 24 " " single brilliant. Cabochon " carbuncle. Star cut, fig. 9. Degree or rose cut, fig. 10.

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.

DIAMOND.

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 by acids 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 or masses 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.

CORUNDUM.

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:

Alumina 98.5 Oxide of iron 1.0 Lime 0.5 ───── 100.

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 RUBY.

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 is heavier, 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.

SAPPHIRE.

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.

FANCY SAPPHIRES.

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 gem stones 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.

STAR SAPPHIRES.

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 bright stripes 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.

SPINEL.

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.

BERYL.

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 a separate division of the beryl family, and is known as the emerald.

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:

Silica 68.50 Alumina 15.75 Glucina 12.50 Peroxide of iron 1. Lime 0.25 Oxide of chrome 0.30 And traces of magnesia, of lime, and of soda.

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.

BERYL.

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 the more 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.

CHRYSOBERYL.

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 various shadings 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.

CYMOPHANE.

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.

ALEXANDRITE.

On the day that the Emperor Alexander of Russia attained his majority the 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.