About the Properties of Apatites, Felspar, and Moonstones

APATITE.

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.

FELSPAR.

Four varieties of felspar are used as gem stones-moonstone or orthoclase, sun-stone or avanturine felspar, Amazon stone or green felspar, and Labrador or Labrador spar.

MOONSTONE.

This variety of felspar is called orthoclase, adularia, and orthose, besides the commercial names of fish-eye, Ceylon or water opal, and in the yellow and red tints sunstone. Moonstone occurs in crystals and crystalline fragments, also massive and granular; its hardness is 6. to 6.5, specific gravity 2.4 to 2.6, refraction double, is not attacked by acids, and is composed of:

Silica 64.5

Alumina 18.5

Potash 17.

With traces of soda.

This beautiful stone is the clearest of all varieties of felspar. It is colorless, or only slightly tinted with blue, green, yellow, and flesh-red, and is transparent to translucent.

The lustre is vitreous, and a brilliant pearly streak of white light plays from side to side.

The yellowish- and reddish-tinted specimens are called sunstones, and are quite rare. These sunstones must not be confounded with the avanturine or felspar sunstone.

Moonstones are found principally in Ceylon and on the St. Gothard in Switzerland, but also occur in Bavaria, Greenland, Tyrol, Dauphine, Norway, and the United States.

During the past few years, large quantities of moonstone balls, cut like whole pearls, have been used for jewelry-the stones being much sought as well because of their beauty as on the ground of the popular superstition that they will bring good luck to the wearer.