168 PRECIOUS STONES
ments; pale yellow, not cleavable; and the common form, bright yellow and granular.
Cassiterite
is composed of stannic acid, 95; ferric acid, 3.4, etc.; specific
gravity, 6.5. Only a few small transparent gems have been cut. It is
found east and west in the United States. Color, brownish white to
reddish brown.
Cave-pearls
are calcareous concretions, formed probably from water-worn pieces of
stalagmite, or pieces Upon which water has deposited successive layers
of carbonate of lime. They are found in the caves of America.
Chiastolite
is a variety of andalusite found in California and Massachusetts. First
found in Andalusia, Spain. It is a curious opaque stone showing
cross-like markings formed by the dissemination of impurities in a
regular manner along the sides, edges, and diagonals of the crystals.
Hardness, 3 and over. Color, black or blackish gray and white.
Chlorastrolite
is found in rolled pebbles, on the beach of Isle Royale, Lake Superior,
where it is cast as it is weathered out of the native underlying rock.
It is opaque, green, mottled, and stellated. It admits of a high
polish, and, when the stellations radiate from the centre, shows a
chatoyancy similar to the cat's-eye. It is composed of silica, alumina,
lime, ferric oxide, soda, and water. Hardness, 5.5 to 6; specific
gravity, 3.2.
Chrysocolla
is a silicate of copper, occurring usually as incrustations, botryoidal
and massive, having no appearance of crystallization or fibrous
structure. It consists of oxide of copper, silica, and water in varying
proportions, sometimes including carbonic acid and oxide of iron.
Hardness, 2 to 3; specific gravity, 2 to 2.3. Translucent to opaque.
Color, bluish green to blue, mottled with darker shades and black.
Mixed or coated with quartz or chalcedony, it is used occasionally.
With the demand for odd stones it is being cut for charms and pendants.
Found in the Lake Superior region and Arizona.
