166 PRECIOUS STONES
in places or speckled with small white spots. Hardness, 6; specific
gravity, 2.4 to 2.6. Acids do not affect it, nor does it yield readily
to the blow-pipe. It consists of silica, alumina, lime, and soda. It is
cut en cabochon and drop shape for brooches and pendants. Subtranslucent.
Apatite is named from the Greek apatad, to
deceive, from an early misunderstanding of its nature. It occurs in
Europe and the United States, and is found as hexagonal prisms, also
massive and of compact fibrous structure. Transparent crystals of
green, pink, and violet, resembling tourmaline, have been found in
Maine. Hardness, 4.5 to 5 ; specific gravity, 3 to 3.2. Lustre
resinous, but somewhat greasy; transparent to opaque. It is composed
principally of sub-sesquiphosphate of lime. Dissolves slowly in nitric
acid, but is infusible under the blow-pipe. Some small crystals are
transparent and colorless, but it is usually green. It is probably
derived from animal fossils, as its constituents are contained in
animal bones and ligaments. It is too soft to cut successfully. Some
phosphoresce when heated, and become electric by friction.
is named after Aragon in Spain, where it was originally found. It is
the " satin spar" sold to tourists at Niagara Falls, and is imported
from Wales. An amber and brown variety is called " California onyx."
Crystallization trimetric in rhombic prisms. Hardness, 3.5 to 4;
specific gravity, 2.9 to 2.10. Lustre vitreous; transparent to
translucent. Cleavage parallel to faces of rhombohedron. Same
composition as calcareous spar: lime, 56; carbonic acid, 44. Falls to
powder before the blow-pipe; effervesces with acids; phosphoresces when
heated. Color, white with tinges of gray, green, yellow, and violet.
called also thummerstein and thumite from Thum in Saxony, is found in
Europe and the United States. Crystallization triclinic, in acute
oblique rhomboidal prisms. It is remarkable for the sharp, thin edges
of its crystals. Hard-