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Ch. 6: Quartz Amethyst

Ch. 6: Quartz Amethyst Page of 515 Ch. 6: Quartz Amethyst Text size:minus plus Restore normal size   Mail page  Print this page
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A POPULAR TREATISE ON GEMS..
choidal ; lustre resinous ; it is semi-transparent and translu­cent; of a blood-red, yellow-brown, or yellow color; fre­quently dark at the outside* growing paler towards the in­side ; the colors are sometimes changing striated ; it scratches white glass, and has a specific gravity of 2·59 to 2-63. There are two varieties known by lapidaries and jewellers which are better than the others ; those having a pale color or yel­lowish tinge, and those having a dark red color; the latter are in the highest estimation, and are called by the French cornalines de vieille roche.
Sardonyx is called a carnelian, having as its principal color the dark-brown or orange-yeliow, interchanged with layers of a white color.
Carnelian onyx has a blood-red base, marked with white stripes. The finest carnelians come from Siberia, India Arabia, Nubia, Surinam, Oberstein in Germany, and Tyrol ; they occur mostly as pebbles or in .cavities of rocks. In the United States they are found on Lake Superior in large quantities, in Missouri, and in Massachusetts. The carne­lian is used for numerous articles in jewelry, such as seals, rings, watch-keys, &c. ; it is cut on a leaden plate with emery, and is polished on wood with pumice stone, and ob­tains its highest polish on a plate composed of lead and tin with rotten stone and water. The form of its cutting is that of pavilion or step cut, on the upper part, and either quadrangular, hexagonal, octangular, or round ; and for raising its lustre or color it is furnished with a. silver or gold foil, or with red paint on its base. The color of the carnelian is also improved by calcination ; the yellowish kind, for instance, by calcining it in a moderate heat and cooling it slowly, may assume a good red color. It is said that the ancients boiled the carnelian in honey in order to heighten its color. Colored figures or drawings may suc-' cessfully be represented by a mixture of white-lead, coleo-
Ch. 6: Quartz Amethyst Page of 515 Ch. 6: Quartz Amethyst
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