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PRECIOUS STONES 169
Cobaltite
is sometimes cut for gem purposes in Europe, and has.the appearance of
a flesh-colored pyrite. It is a sulphide of cobalt. Crystallization
cubic. Hardness, 5.5; specific gravity, 6.3 to 6.4.
Compact titanic iron takes a high polish, and is sometimes cut for ornaments. It is found in Rhode Island and Arkansas.
Coral
is the product of a family of zoophytes. These polyps make this
substance in the cavities of rocks, several hundred feet under the
surface of the sea. It is found in branches of irregular shapes,
varying from twelve inches to several feet long, and an inch or less in
diameter at the thickest part. It is found off the coasts of Africa and
Corsica. Red is the usual color, though it is occasionally found in
white and black. A wild-rose pink is the color most desired.
Cyanite, or kyanite, is named from the Greek kyanos, sky-blue.
It is also called sappar, a corruption of sapphire; also disthene. It
is found in Europe, the East Indies, and North America. Crystallization
triclinic, in thin bladed crystals massed together. Lustre vitreous to
pearly; transparent. Hardness, 5 to 7; specific gravity, 3.4 to 3.7.
Composition: silica, 37; alumina, 63; with a small percentage of ferric
oxide. Lateral cleavage distinct. It is infusible before the blow-pipe;
melts with borax, but is not attacked by acids.
Danburite
is seldom found clear enough to cut into gems. The finest, which are
colorless, come from Switzerland. It is found also in Connecticut and
New York State. It is a silicate of lime and boracic acid. Hardness, 7
to 7.2 ; specific gravity, 2.96. Color, wine, honey, or yellowish brown.
Datolite,
or datholite, is a borosilicate of lime found in the Lake Superior
copper region, Connecticut, and New Jersey. Crystallization trimetric,
in hemihedral prisms. Crystals are small and glassy, and without
distinct cleavage; also botryoidal. Composition: silica, 37.4; lime,
35.7; boracic
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