Sal am stone

is a variety which consists of small transparent crystals, generally six-sided prisms, of pale reddish and bluish colours. The corundum of Batta gam man a is frequently found in large six-sided prisms: it is commonly of a brown colour, whence it is called by the natives curundu gallé , cinnamon stone. The hair-brown and reddish-brown crystals are called adamantine spar. Sapphire and sal am stone are chiefly met with in secondary repositories, as in the sand of rivers ., accompanied by crystals and grains of octahedral iron-ore and of several species of gems. Corundum is found in imbedded crystals in a rock, consisting of india nite. Adamantine spar occurs in a sort of granite. The finest varieties of sapphire come from Pegu, where they occur in the Capelan mountains near Syrian. Some have been found also at Hohenstein in Saxony, Bilin in Bohemia, Puy in France, and in several other countries. The red variety, the ruby, is most highly valued. Its colour is between a bright scarlet and crimson. A perfect ruby above 3 1 ⁄ 2 carats is more valuable than a diamond of the same weight. If it weigh one carat, it is worth 10 guineas; 2 carats, 40 guineas; 3 carats, 150 guineas; 6 carats, above 1000 guineas. A deep coloured ruby, exceeding 20 carats in weight, is generally called a carbuncle; of which 108 were said to be in the throne of the Great Mogul, weighing from 100 to 200 carats each; but this statement is probably incorrect. The largest oriental ruby known to be in the world, was brought from China to Prince Gargarin, governor of Siberia. It came afterwards into the po e ion of Prince Menzikoff, and constitutes now a jewel in the imperial crown of Ru ia. A good blue sapphire of 10 carats is valued at 50 guineas. If it weighs 20 carats, its value is 200 guineas; but under 10 carats, the price may be estimated by multiplying the square of its weight in carats into half a guinea; thus, one of 4 carats would be worth 4 2  × 1 ⁄ 2 G. = 8 guineas. It has been said that the blue sapphire is superior in hardne to the red, but this is probably a mistake arising from confounding the corundum ruby with the spinelle ruby. A sapphire of a barbel blue colour, weighing 6 carats, was disposed of in Paris by public sale for 70 l. sterling; and another of an indigo blue, weighing 6 carats and 3 grains, brought 60 l. ; both of which sums much exceed what the preceding rule a igns, from which we may perceive how far fancy may go in such matters. The sapphire of Brasil is merely a blue tourmaline, as its specific gravity and inferior hardne show. White sapphires are sometimes so pure, that when properly cut and polished they have been pa ed for diamonds. The yellow and green sapphires are much prized under the names of Oriental topaz and emerald. The specimens which exhibit all these colours a ociated in one stone are highly valued, as they prove the mineralogical identity of these varieties. Besides these shades of colour, sapphires often emit a beautiful play of colours, or chatoiement , when held in different positions relative to the eye or incident light; and some likewise present star-like radiations, whence they are called star-stones or asterias ; sending forth 6 or even 12 rays, that change their place with the position of the stone. This property so remarkable in certain blue sapphires, is not however peculiar to these gems. It seems to belong to transparent minerals which have a rhomboid for their nucleus, and arises from the combination of certain circumstances in their cutting and structure. Lapidaries often expose the light-blue variety of sapphire to the action of fire, in order to render it white and more brilliant; but with regard to those found at Expailly in France, fire deepens their colour. 3. Chrysoberyl , called by Haüy Cymophane, and by others Prismatic corundum, ranks next in hardne to sapphire, being 8·5 on the same scale of estimation. Its specific gravity is 3·754. It usually occurs in rounded pieces about the size of a pea, but it is also found crystallised in many forms, of which 8-sided prisms with 8-sided summits are perhaps the most frequent. Lustre vitreous; colour asparagus green, pa ing into greenish-white and olive-green. It shows a bluish opalescence, a light undulating as it were in the stone, when viewed in certain directions; which property constitutes its chief attraction to the jeweller. When polished, it has been sometimes mistaken for a yellow diamond; and from its hardne and lustre is considerably valued. Good specimens of it are very rare. It has been found only in the alluvial deposits of rivers, along with other species of gems. Thus it occurs in Brasil, along with diamonds and prismatic topaz; also in Ceylon. Its constituents are, alumina 68·66; glucina 16·00; silica 6·00; protoxide of iron 4·7; oxide of titanium 2·66; moisture 0·66, according to Seybert’s analysis of a specimen from Brasil. It is difficultly but perfectly fusible before the blowpipe, with borax and salt of phosphorus. In composition it differs entirely from sapphire, or the rhombohedral corundum. 4. Spinelle Ruby , called Dodecahedral corundum by some mineralogists, and Balas ruby by lapidaries. Its hardne is 8. Specific gravity 3·523. Its fundamental form is the hexahedron, but it occurs crystallized in many secondary forms: octahedrons, tetrahedrons and rhombohedrons. Fracture conchoidal; lustre vitreous; colour red, pa ing into blue and green, yellow, brown and black; and sometimes it is nearly white. Red spinelle consists of, alumina 74·5; silica 15·5; magnesia 8·25; oxide of iron 1·5; lime 0·75. Vauquelin discovered 6·18 per cent. of chromic acid in the red spinelle. The red varieties exposed to heat, become black and opaque; on cooling they appear first green, then almost colourle , but at last resume their red colour. Pleonaste is a variety which yields a deep green globule with borax. Crystals of spinelle from Ceylon have been observed imbedded in limestone, mixed with mica, or in rocks containing adularia, which seem to have belonged to a primitive district. Other varieties like the pleonaste occur in the drusy cavities of rocks ejected by Vesuvius. Crystals of it are often found in diluvial and alluvial sand and gravel, along with true sapphires, pyramidal zircon, and other gems, as also with octahedral iron ore, in Ceylon. Blue and pearl-gray varieties occur in Süderm ann land in Sweden, imbedded in granular limestone. Pleonaste is met with also in the diluvial sands of Ceylon. Clear and finely coloured specimens of spinelle are highly prized as ornamental stones. When the weight of a good spinelle exceeds 4 carats, it is said to be valued at half the price of a diamond of the same weight. M. Brard has seen one at Paris, which weighed 215 grains. 5. Zircon or Hyacinth . Its fundamental form is an isosceles 4-sided pyramid; and the secondary forms have all a pyramidal character. Fracture conchoidal, uneven; lustre more or le perfectly adamantine; colours, red, brown, yellow, gray, green, white; which with the exception of some red tints, are not bright. Hardne 7·5. Specific gravity 4·5. Zircon and hyacinth consist, according to Klaproth, of almost exactly the same constituents; namely, zirconia 70; silica 25; oxide of iron 5. In the white zirconia there is le iron and more silica. Before the blowpipe the hyacinth loses its colour, but does not melt. The brighter zircons are often worked up into a brilliant form, for ornamenting watch cases. As a gem, hyacinth has no high value. It has been often confounded with other stones, but its very great specific gravity makes it to be readily recognized. 6. Topaz. The fundamental form is a scalene 4-sided pyramid; but the secondary forms have a prismatic character; and are frequently observed in oblique 4-sided prisms, acuminated by 4 planes. The lateral planes of the prism are longitudinally striated. Fracture conchoidal, uneven; lustre vitreous; colours, white, yellow, green, blue, generally of pale shades. Hardne 8; specific gravity 3·5. Prismatic topaz consists, according to Berzelius, of alumina 57·45; silica 34·24; fluoric acid 7·75. In a strong heat the faces of crystallization, but not those of cleavage, are covered with small blisters, which however immediately crack. With borax, it melts slowly into a transparent gla . Its powder colours the tincture of violets green. Those crystals which po e different faces of crystallization on opposite ends, acquire the opposite electricities on being heated. By friction, it acquires positive electricity. Most perfect crystals of topaz have been found in Siberia, of green, blue, and white colours, along with beryl, in the Uralian and Altai mountains, as also in Kamschatka; in Brazil, where they generally occur in loose crystals, and pebble forms of bright yellow colours; and in Mucla in Asia Minor, in pale straw-yellow regular crystals. They are also met with in the granitic detritus of Cairngorm in Aberdeen shire. The blue varieties are absurdly called oriental aquamarine by lapidaries. If exposed to heat, the Saxon topaz loses its colour and becomes white; the deep yellow Brazilian varieties a ume a pale pink hue; and are then sometimes mistaken for spinelle, to which, however, they are somewhat inferior in hardne . Topaz is also distinguishable by its double refractive property. Tavernier mentions a topaz, in the po e ion of the Great Mogul, which weighed 157 carats, and cost 20,000 l. sterling. There is a specimen in the museum of natural history at Paris which weighs 4 ounces 2 gros. Topazes are not scarce enough to be much valued by the lapidary. 7. Emerald and Beryl , are described in their alphabetical places. Emerald loses its lustre by candle-light; but as it appears to most advantage when in the company of diamonds, it is frequently surrounded with brilliants, and occasionally with pearls. Beryl is the aqua-marine of the jewellers, and has very little estimation among lapidaries. 8. Garnet . See this stone in its alphabetical place. 9. Chrysolite , called Peridot by Haüy; probably the topaz of the ancients, as our topaz was their chrysolite. It is the softest of the precious stones, being scratched by quartz and the file. It refracts double. 10. Quartz , including, as sub-species, Amethyst , Rock-crystal , Rose-quartz , Prase or Chrysoprase , and several varieties of calcedony, as Cat’s eye , Plasma , Chrysoprase , Onyx , Sardonyx , . Lustre vitreous, inclining sometimes to resinous; colours, very various; fracture conchoidal; hardne , 7; specific gravity, 2·69. 11. Opal , or uncleavable quartz. Fracture, conchoidal; lustre, vitreous or resinous; colours, white, yellow, red, brown, green, gray. Lively play of light; hardne , 5·5 to 6·5; specific gravity, 2·091. It occurs in small kidney-shaped and stalactitic shapes, and large tuberose concretions. The phenomena of the play of colours in precious opal has not been satisfactorily explained. It seems to be connected with the regular structure of the mineral. Hydrophane, or oculis mundi, is a variety of opal without transparency, but acquiring it when immersed in water, or in any transparent fluid. Precious opal was found by Klaproth to consist of silica, 90; water, 10; which is a very curious combination. Hungary has been long the only locality of precious opal, where it occurs near Caschau, along with common and semi-opal, in a kind of porphyry. Fine varieties have, however, been lately discovered in the Faroe islands; and most beautiful ones, sometimes quite transparent, near Gracias a Dios, in the province of Honduras, America. The red and yellow bright coloured varieties of fire-opal are found near Zimapan, in Mexico. Precious opal, when fashioned for a gem, is generally cut with a convex surface; and if large, pure, and exhibiting a bright play of colours, is of considerable value. In modern times, fine opals of moderate bulk have been frequently sold at the price of diamonds of equal size; the Turks being particularly fond of them. The estimation in which opal was held by the ancients is hardly credible. They called it Paideros, or Child beautiful as love. Nonius, the Roman senator, preferred banishment to parting with his favourite opal, which was coveted by Mark Antony. Opal which appears quite red when held against the light, is called girasol by the French; a name also given to the sapphire or corundum asterias or star-stone. 12. Turquois , or Calaite . Mineral turquois, occurs ma ive; fine-grained impalpable; fracture conchoidal; colour, between a blue and a green, soft, and rather bright; opaque; hardne , 6; spec. grav. 2·83 to 3·0. Its constituents are, alumina, 73; oxide of copper, 4·5; oxide of iron, 4; water, 18; according to Dr. John. But by Berzelius, it consists of phosphate of alumina and lime, silica, oxides of copper and iron, with a little water. It has been found only in the neighbourhood of Nichabour in the Khor as san, in Persia; and is very highly prized as an ornamental stone in that country. There is a totally different kind of turquois, called bone turquois , which seems to be phosphate of lime coloured with oxide of copper. When the oriental stone is cut and polished, it forms a pleasing gem of inferior value. Malachite , or mountain green, a compact carbonate of copper, has been substituted sometimes for turquois, but their shades are different. Malachite yields a green streak, and turquois a white one. 13. Lapis lazuli , is of little value, on account of its softne .