| Crookesite | |
|---|---|
| General | |
| Category | Selenide mineral |
| Chemical formula | Cu7(Tl,Ag)Se4 |
| Strunz classification | 02.BD.50 |
| Identification | |
| Color | Lead-gray |
| Crystal habit | As finely divided, disseminated specks, and as small veinlets. |
| Crystal system | Tetragonal - Disphenoidal |
| Cleavage | Good, two at right angles |
| Fracture | Brittle |
| Mohs scale hardness | 2.5–3 |
| Luster | Metallic |
| Diaphaneity | Opaque |
| Specific gravity | 6.90 |
| References | [1][2] |
Crookesite is a selenide mineral composed of copper and selenium with variable thallium and silver.
Contents |
Its chemical formula is reported either as Cu7(Tl,Ag)Se4 or (Cu,Tl,Ag)2Se.[3] It is formed by precipitation from hydrothermal fluids, and contains by mass: 16.3% Tl, 47.3% Cu, 2.9% Ag, and 33.6% Se.[1]
Crookesite is an opaque, bluish grey to pink toned brown metallic mineral crystallizing in the tetragonal system. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 6.9.
It was discovered in 1866 in Skrikerum, Sweden and named for Sir William Crookes (1832-1919), the discoverer of the element thallium.[1]