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PRECIOUS STONES.
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soda, and water ; it does not crystallize, but is found in
masses with bands arranged in concentric layers of different shades of dark green. With a hardness, in some specimens, equal to quartz, it admits of a good polish, — a quality, together with its fine color, constituting it an agreeable gem-stone. The name is a combination of three words, meaning " banded green stone." Diopside.— The name diopside, meaning " double appearance," was given to a variety of pyroxene, on account of its
dichroism ; its range of color includes white, brown, and various shades of green resembling green tourmaline, or green epidote. Though softer than quartz, the transparent crystals are cut for gems. The Tyrol is the best known locality for this mineral on the Eastern Continent, but fine specimens, weighing from six to fifteen carats, comparing favorably with the imported stones, have been discovered at De Kalb, New York, said to be the only place in this country where they have been found. Dioptasc. — The mineral known as dioptase, signifying " to
look through," regarded by some lithologists as a green variety of the beryl, is classed by Dana as a species, closely allied, however, to that precious stone, though differing in hardness, specific gravity, and chemical composition, which consists of a large proportion of oxide of copper. The crystals are transparent to translucent, and possess the quality of double refraction in a high degree ; it closely resembles the emerald in appearance, for which it is sometimes sold. It is very limited in its natural distribution, occurring almost exclusively in the Kirghiz Steppes, Siberia, where it was discovered and named achirite. Epidote. — The epidote, occasionally employed as a gemstone, is sometimes denominated green schorl. The predomi-
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