TOURMALINE, in mineralogy, a species of siliceous earth.
It has been found only in Ceylon, Brazil, and Tyrol. That of Ceylon is of a dark brown or yellowish colour; its specific gravity 3.065, or 3.295; that of Brazil is green, blue, red, or yellow, and its specific gravity 3.075 or 3.180; that of Tyrol by reflected light is of a blackish brown, but by refracted light yellowish, or in thin pieces green; its specific gravity 3.050; mostly crystallized in polygonal prisms, but sometimes amorphous. The thickest parts are opaque: the thin more or less transparent.
The proportion of their constituent parts has been found by Bergman,
| Tourmaline | |||
|---|---|---|---|
| of Tyrol. | of Ceylon. | of Brazil. | |
| Argill. | 42 | 39 | 50 |
| Silex, | 40 | 37 | 34 |
| Calcareous earth, | 12 | 15 | 11 |
| Iron, | 6 | 9 | 5 |
| 100 | 100 | 100 | |
For the electrical qualities of tourmaline, see ELECTRICITY, no 54.