Apatite, which is seldom used as a gem stone, sometimes resembles the
beryl and emerald, but is much softer and rarely has the color and
brightness combined of the former gems.
This mineral, composed principally of subsesquiphosphate of lime,
is 4.5 to 5. in hardness, has the specific gravity of 2.95 to 3.25,
is transparent to opaque, vitreous in lustre, infusible before the
blow-pipe, and dissolves slowly in nitric acid. In colors, apatite
varies from colorless to sea-green, bluish-green, violet-blue, gray,
yellow, red, and brown.
Apatite is found in Saxony, the Hartz Mts., Bohemia, Norway, Bavaria,
England, St. Gothard in Switzerland, and in the United States.