Part 18

Transparent or strongly translucent specimens, in handsome green or brown varieties, are used for jewelry, principally, however, in Turin and Naples.

Chrysolite and green garnet are sometimes substituted for vesuvianite. The first has a greater specific gravity and is more vivid in color, and the latter is also heavier and harder.

EUCLASE.

Euclase is very brittle, and therefore is rarely used as an ornamental stone.

This mineral has the hardness of 7.5; specific gravity, 3.1; lustre, vitreous to pearly; it is transparent to semi-transparent, doubly refractive, is not acted upon by acids, fuses under the blow-pipe to a white enamel, and is composed of:

Silica 41.2 Alumina 35.2 Glucina 17.4 Water 6.2

Euclase occurs in Brazil, in the neighborhood of Villa Rica, and also in the Urals, in colorless, pale green, blue, pale yellow, and white colors.

SPHENE.

Sphene or titanite is also a brittle mineral, 5 to 5.5 in hardness; specific gravity, 3.4 to 3.56; transparent, doubly refractive; lustre, adamantine to resinous; colors, brown, gray, yellow, green, black, and colorless; and composition:

Silica 31 Titanium oxide 41 Lime 27 Ferrous oxide 1

When transparent in colorless, greenish, or yellow colors, this mineral presents an appearance like the fire opal.

Sphene is found in Switzerland, the Urals, Tyrol, Finland, Wales, Ireland, Germany, Canada, and the United States.

PHENACITE.

This mineral, rarely used as a gem stone, is 7.5 to 8 in hardness; specific gravity, 2.96 to 3; lustre, vitreous; transparent to semi-translucent, doubly refractive, it does not melt before the blow-pipe, and contains:

Silica 54.2 Glucina 45.8

Phenacite occurs colorless, and also bright wine-yellow inclining to red, and brown. This stone is found in Russia, Mexico, and Alsace.

The colorless or transparent variety approaches the diamond in brilliancy, especially under artificial light.

EPIDOTE.

Epidote usually occurs in a peculiar yellowish-green, called pistachio green, a color that is seldom found in other minerals. Besides this color, olive, brownish-green, greenish-black and black, red, yellow-gray, and grayish-white occur. The hardness of epidote is 6 to 7; specific gravity, 3.32 to 3.50; lustre, vitreous to pearly; refraction, double. The stone is transparent to opaque, is attacked by acids, and is slightly affected by the blow-pipe. It is composed of:

Silica 38 Alumina 22 Ferric oxide 15 Lime 23 Water 2

Epidote is found in Norway, Saxony, Siberia, Brazil, on the St. Gothard, in Switzerland, in the Tyrol, and in the Hartz.

AXINITE.

Axinite is a brittle mineral which has occasionally furnished some pretty gem stones.

The hardness of this stone is 6.5 to 7; specific gravity, 3. to 3.3; lustre, vitreous. It is transparent to translucent, is not attacked by acids, and melts readily before blow-pipe. It is composed of:

Silica 43 Lime 20 Alumina 16 Ferric oxide 10 Boron trioxide 5 Manganese dioxide 3 Magnesia 2 Potash 1

Axinite occurs in clove-brown, plum-blue, and pearl-gray, and exhibits trichroism. The best specimens come from St. Christophe in Dauphiny, but it is also found at Santa Maria, and in Switzerland, Sweden, England, Chili, Saxony, the Hartz Mountains, and the United States.

Axinite is usually cut, like the opal, cabochon, but is rarely used as a gem stone.

DIOPSIDE.