750
LEAD.
low colors; and in Mucla, in Asia Minor , in pale straw-yellow regular crystals. TWare also met with in the granitic detritus of Cairngorm , in Aberdeenshire . The blnvarieties are absurdly called oriental aquamarine, by lapidaries. If exposed to heat, t»Saxon topaz loses its color and becomes white; the deep yellow Brazilian varieties aS "sume a pale pink hue ; and are then sometimes mistaken for spinelle, to which, however,they are somewhat inferior in hardness. Topaz is also distinguishable by its doubrefractive property. Tavernier mentions a topaz, in the possession of the Great Mog u ;Jwhich weighed 157 carats, and cost 20,0001. sterling. There is a specimen in the museumof natural history at Paris which weighs 4 ounces 2 gros.
Topazes are not scarce enough to be much valued by the lapidary. ., s
7. Emerald and Beryl are described in their alphabetical places. Emerald l° seS j-g.lustre by candle-light; but as it appears to most advantage when in the company ofmonds, it is frequently surrounded with brilliants, and occasionally with pearls. Beiy*the aquamarine of the jewellers, and has very little estimation among lapidaries.
8. Garnet . See this stone in its alphabetical place. »
9. Chrysolite, called Peridot, by Haiiy; probably the topaz of the ancients, as our top
was their chrysolite. It is the softest of the precious stones, being scratched by 9 uaand the file.' It refracts double. gt
10. Quartz, including, as sub-species, Amethyst , Rock-crystal, Rose-quartz, Prase,
Chrysoprase , and several varieties of calcedony, as Cat ’s-eye, Plasma, Chrysqprase, ,* sSardonyx, &c. Lustre, vitreous, inclining sometimes to resinous; colors, very van 0 ’fracture, conchoidal; hardness, 7 ; specific gravity, 2-69. . g .
11. Opal , or uncleavable quartz. Fracture, conchoidal; lustre, vitreous or resino Jcolors, white, yellow, red, brown, green, gray. Lively play of light; hardness
5-5 t0
6-5; specific gravity, 2-091. It occurs in small kidney-shaped and stalactitic s ^ a ^ u " sand large tuberose concretions. The phenomena of the play of colors in P re ^J,jaiopal has not been satisfactorily explained. It seems to be connected with the ra ° hoU tstructure of the mineral. Hydrophane, or oculis mundi, is a variety of opaltransparency, but acquiring it when immersed in water, or in any transparent #
Precious opal was found by Klaproth to consist of silica, 90; water, 10 ; which ,
very curious combination. Hungary has been long the only locality of precious V _where it occurs near Caschau, along with common and semi-opal, in a kind of P° r A,gaU-Finc varieties have, however, been lately discovered in the Faroe islands ; andtiful ones, sometimes quite transparent, near Gracias a Dios, in the province of Hras, America . The red and yellow bright colored varieties of fire-opal are founu aZimapan, in Mexico . Precious opal, when fashioned for a gem, is generally CU J W nS jd-convex surface; and if large, pure, and exhibiting a bright play of colors, is °* s0 lderable value. In modern times, fine opals of moderate bulk have been frequently ^at the price of diamonds of equal size : the Turks being particularly fond of them j le d itestimation in which opal was held by the ancients is hardly credible. They c ^ JD eo tPaideros, or Child beautiful as love. Nonius, the Roman senator, preferred bani ^ a p,to parting with his favorite opal, which was coveted by Mark Antony . Opal wn a lsopears quite red when held against the light, is called g irasol by the French ; a ngiven to the sapphire or corundum asterias or star-stone. . a ]pahl e >
12. Turquois or Calaite. Mineral turquois occurs massive; fine-grained, iWP g U e;fracture, conchoidal; color, between a blue and a green, soft, and rather bright, c0 pper,hardness, 6 ; spec, grav., 2-83 to 3-0. Its constituents are alumina, 73 ; oxyde o conS ;gts4-5; oxyde of iron, 4; water, 18; according to Dr. John. But by Berzelius , j. wa ier.of phosphate of alumina and lime, silica, oxydes of copper, and iron, with a B ^ p ers ia jIt has been found only in the neighborhood of Nichabour in the Khorassan , 1 ^jy dif*and is very highly prized as an ornamental stone in that country. There IS a . e co loreuferent kind of turquois, called bone turquois, which seems to be phosphate ol i ^ pj ea singwith oxyde of copper. When the oriental stone is cut and polished, it form s ^ c opPf T>gem of inferior value. Malachite, or mountain green, a compact carbonate ^^ebitehas been substituted sometimes for turquois, but their shades are different.
yields a green streak, and turquois a white one.
13. Lapis lazuli is of little value, on account of its softness. . ,iy
LEAD ( Plomb , Fr.; Blei, Germ.). This is one of the metals most anC ~ 1 -.p a brig®
being mentioned in the books of Moses. It has a gray-blue color, t ,.j n g in tametallic lustre when newly cut, but it becomes soon tarnished and earthy „ c fljre! *air. Its texture is close, without perceptible cleavage or appearance o - 11-3® .
specific gravity of common lead is 11-352; but of the pure metal, “ . fusfW®
11-44. It is very malleable and ductile, but soft and destitute of e a c00 Hng, fJ jat 612° Fahr., by Crighton, at 634° by Kupfer , and crystallizable on four -sid eoctahedrons implanted into each other so as to form an assemblagepyramids.