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 polygon prisms, but sometimes amorphous. The thickest parts are opake; 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 |

For the electrical qualities of tourmaline, see ELECTRICITY, p. 54.