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.
Diopside is cut and sometimes sold in Turin and in Chamouny as a gem stone, but no great quantity of this mineral is used for ornamental purposes.
The hardness of diopside is 5 to 6; specific gravity, 2.9 to 3.5; lustre, vitreous to greasy. It is transparent to translucent, brittle, cannot be dissolved by acids, and melts before the blow-pipe. It is composed of:
| Silica | 54 |
| Lime | 24 |
| Magnesia | 18 |
| Ferrous oxide | 4 |
This mineral is grayish-white to pearl-gray, and greenish-white to greenish-gray. The best green transparent specimens are from the Mussa Alp and Zillerthal, but it is also found in the Urals and the United States.