Category Selenide mineral Strunz classification 2.BD.50 Space group I4 | Formula
(repeating unit) Cu7(Tl,Ag)Se4 Crystal system Tetragonal | |
Crystal class Disphenoidal (4)
H-M symbol: (4) | ||
Crookesite is a selenide mineral composed of copper and selenium with variable thallium and silver.
Contents
Characteristics
Its chemical formula is reported either as Cu7(Tl,Ag)Se4 or (Cu,Tl,Ag)2Se. 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.
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.
Name and discovery
It was discovered in 1866 in Skrikerum, Sweden and named for Sir William Crookes (1832–1919), the discoverer of the element thallium.
References
Crookesite Wikipedia(Text) CC BY-SA