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152 A Book of Precious Stones
At
present it is customary to call those which incline most to yellow "
chrysolite "; the yellowish green, resembling a light tourmaline with a
dash of yellow, is known by the name " peridot," given to it by the
French jewellers; and " olivine " is the name associated with the
brighter yellowish emerald-green variety, although originally the
yellow to olive-green stones were known by that name.
Few
olivines are sold as such. The beautiful bright yellowish-green stones
known here as olivines, are generally demantoids, Eussian green
garnets, of about the same hardness; these are rarely found large
enough to cut to gems of over one half to three quarters of a carat.
Olivine
crystallises in the orthorhombic system; also occurring massive;
compact or granular; usually in embedded grains; hardness, 6.5 to 7;
specific gravity, 3.33 to 3.44; cleavage, distinct; fracture,
conclioidal; brittle; lustre, vitreous; colour, typical, olive green;
brownish, greyish red and black. It is strongly doubly refractive with
marked dichroism in some specimens ; peridot showing straw-green and a
green image. Gem kinds and their colours are chrysolite, yellowish
green; peridot or "evening emerald," olive pistachio, or leek-green
colour, of a hue more subdued than the emerald—green beryl. The
approved tint of peridot resembles that revealed by looking through a
delicate translucent
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