| Crookesite | |
|---|---|
 | |
| General | |
| Category | Selenide mineral |
| Formula | Cu 7(Tl,Ag)Se 4 |
| IMA symbol | Crk[1] |
| Strunz classification | 2.BD.50 |
| Crystal system | Tetragonal |
| Crystal class | Disphenoidal (4) H-M symbol: (4) |
| Space group | I4 |
| Identification | |
| Color | Lead-gray |
| Crystal habit | As finely divided, disseminated specks, and as small veinlets. |
| Cleavage | Good, two at right angles |
| Fracture | Brittle |
| Mohs scale hardness | 2.5–3 |
| Luster | Metallic |
| Diaphaneity | Opaque |
| Specific gravity | 6.90 |
| References | [2][3] |
Crookesite is aselenidemineral composed ofcopper andselenium with variablethallium andsilver.
Its chemical formula is reported either asCu
7(Tl,Ag)Se
4 or(Cu,Tl,Ag)
2Se.[4] It is formed by precipitation fromhydrothermal fluids, and contains by mass: 16.3% Tl, 47.3% Cu, 2.9% Ag, and 33.6% Se.[2]
Crookesite is an opaque, bluish grey to pink toned brown metallic mineral crystallizing in thetetragonal system. It has aMohs hardness of 2.5 to 3 and aspecific gravity of 6.9.
It was discovered in 1866 in Skrikerum, Sweden and named for SirWilliam Crookes (1832–1919), the discoverer of the element thallium.[2]
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