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170 PRECIOUS STONES
acid,
21.3; water, 5.7. Translucent to opaque. Hardness, 5 to 5.5; specific
gravity, 2.9 to 3. Color, white, creamy, and flesh-colored.
Dioptase
is a brilliant green silicate of copper found as rhombohedral crystals
and hexagonal prisms in the cavities of mahogany ore. Lustre vitreous;
transparent to nearly opaque. Hardness, 4.5 ; specific gravity, 3.28.
It is too soft for use as a gem.
Elseolite is named from elaion, oil,
and is a variety of nepheline. It is found in Norway, Siberia,
Arkansas, and Maine, in dingy, subtranslucent, cleavable masses. Lustre
vitreous to greasy. Hardness, 5.5 to 6; specific gravity, 2.4 to 2.65.
Composition: silica, 43.4; alumina, 33.5, with soda, potash, peroxide
of iron, lime, and water. Color, bluish.
Enstatite
and bronzite are found in Pennsylvania and Maryland. If cut across the
fibre, they show a cat's-eye effect, but none have been found
sufficiently fine to cut for gems. Color, dark green or greenish brown,
with a lustre like bronze.
Epidote,
of which zoisite and thulite are varieties, is a translucent to opaque
stone, transparent only in very small crystals. Crystallization
monoclinic, in right rhomboidal prisms, often with six or more sides.
Hardness, 6 to 7; specific gravity, 3.3 to 3.4. Lustre vitreous to
pearly. Cleavage parallel to side planes. Refraction double.
Composition varies considerably in proportions of silica, alumina,
lime, and ferric oxide, mainly. It is attacked by acids, and slightly
affected by the blow-pipe. The usual color is pistachio-green; it also
ocurs in gray to grayish green, and blue with brownish and reddish
modifications. It is found in Europe, Brazil, and the United States.
Magnesian epidote contains fourteen per cent, of oxide of manganese.
Euclase is a rare mineral, which has, however, been cut and polished. Crystallization trimetric, in prismatic crystals
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