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Ch. 6: Diamond

Ch. 6: Diamond Page of 515 Ch. 6: Diamond Text size:minus plus Restore normal size   Mail page  Print this page
186
A POPULAR TREATISE ON GEMS.
pistachio-nut green colors. The blue color is very rare. The blue diamond of Mr. Hope, of London, is one of ex­treme beauty and rarity, and is of immense value; the yellow diamond in the Museum of Natural History, in Paris, is likewise very remarkable for its color and size. The black diamond, which is perfectly black, although plainly crystallized, occurs most frequently in small bristled balls, but crystalline points; the crystals are very small, grouped together in an irregular manner, and extremely refractory to the cut; it is considered the hardest of all diamonds. The green diamond is also very rare, but I have seen some beautiful specimens in the Jardin des Plantes and in Freiberg, the first in the cabinet of Abbe Hauy, and the latter in the cabinet of Werner. Its streak powder is- white or grayish ; it becomes phosphorescent by the rays of the sun, and electric by rubbing, which property it retains for half an hour; its specific gravity is 3-5-3-6 ; it does not alter before the blowpipe; it burns, however, at a high degree of heat, and in atmospheric air with a bluish flame; its touch is very cold ; it consists of carbon. The diamond bears the same name in trade, but is changed according to its cut; the blackish and brownish diamonds are called the Savoy diamonds (Diamants Savoyards). The compact and amorphic diamond was first brought to notice by the experiments of Mr. Dufrenoy, about five years ago, as being the transition from the crystallized to the compact condition, on account of its hardness and specific gravity, and has become a great article of commerce; it cuts glass, scratches quartz and topaz, has a specific gravity of 3.27-3.52, and is completely consumed in oxygen gas; it occurs in kidney-shaped and irregular angular masses, but not in pebbles; the exterior is generally black, sometimes resem­bling the graphite; somewhat resinous lustre, and fre­quently its form is very singular, the outside coating being
Ch. 6: Diamond Page of 515 Ch. 6: Diamond
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