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CHRYSOBERYL
This mineral is like beryl in containing the element glucinum (beryllium), but in other respects is a distinct species. Chrysoberyl has no silica in its composition, as has beryl, but is composed of glucina and alumina, the theoretical percentages being glucina 19.8, alumina 80.2. In nature, however, some other oxides are usually present as impurities or replacing the alumina. Such are iron and chromium oxides. Chrysoberyl is remarkable for its hardness, this being 8.5, and thus near that of corundum. The cut stones therefore retain a polish well. The specific gravity of the mineral is somewhat greater than that of the diamond, being 3.5 to 3.8. It crystallizes in the orthorhombic system, and often forms twins which are so united as to make a six-rayed stellate crystal, or six-sided prisms. An illustration of one of these crystals may be seen in the colored plate. Chrysoberyl has a prismatic cleavage and conchoidal fracture. Its luster is vitreous, tending to oily, and is brilliant. The mineral is infusible, and is not attacked by acids. In color it usually presents some shade of green, tending at times to brown or yellow. The name chrysoberyl means literally golden beryl, and suggests a yellow stone. While this is a common color, grass-green and emerald-green are frequent and characteristic. Among jewelers chrysoberyl, especially the Brazilian chrysoberyl, is often known as chrysolite, a custom which has doubtless arisen through the similarity in color of the two minerals. Three kinds of chrysoberyl are employed in jewelry, and being given different names may be considered separately. These are: (1) ordinary chrysoberyl, (2) cymophane, or cat's-eye, and (3) alexandrite. Ordinary chrysoberyl, also called Oriental chrysolite, or chrysolite, is greenish-yellow to smoky-brown in color, and is employed as a gem only when transparent. It is for the most part obtained in Brazil and Ceylon, in the gem gravels of both of which countries it occurs. The Brazilian chrysoberyls are rolled pebbles, scarcely larger than beans, and occur together with topaz, garnet, tourmaline, quartz, etc., in the beds of streams chiefly in the northern part of the province of Minas Geraes. The stones occur in the neighborhood of granite and gneiss, and were therefore probably originally formed in these rocks. The (Ceylonese chrysoberyls are likewise found in stream beds, and come from Saifra-
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