Chemistry:Crookesite

From HandWiki
Crookesite
Crookesite.jpg
General
CategorySelenide mineral
Formula
(repeating unit)
Cu7(Tl, Ag)Se4
Strunz classification2.BD.50
Crystal systemTetragonal
Crystal classDisphenoidal (4)
H-M symbol: (4)
Space groupI4
Identification
ColorLead-gray
Crystal habitAs finely divided, disseminated specks, and as small veinlets.
CleavageGood, two at right angles
FractureBrittle
Mohs scale hardness2.5–3
|re|er}}Metallic
DiaphaneityOpaque
Specific gravity6.90
References[1][2]

Crookesite is a selenide mineral composed of copper and selenium with variable thallium and silver.

Characteristics

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.

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.[1]

See also

References