Chemistry:Crookesite

Short description: Selenide of copper, thallium and silver

Crookesite
General
Category	Selenide mineral
Formula (repeating unit)	Cu7(Tl, Ag)Se4
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
|re|er}}	Metallic
Diaphaneity	Opaque
Specific gravity	6.90
References

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. 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.

See also

• List of minerals
• List of minerals named after people
• Sabatierite

References

• Berger, Rolf A.; Sobott, Robert J. (1987). "Characterization of TlCu₇S₄, a crookesite analogue". Monatshefte für Chemie 118 (8–9): 967–972. doi:10.1007/BF00815324. 
• Berger, R..A. (1987). "Crookesite and sabatierite in a new light. A crystallographer's comment". Zeitschrift für Kristallographie 181 (1–4): 241–249. doi:10.1524/zkri.1987.181.1-4.241. Bibcode: 1987ZK....181..241B. http://rruff.geo.arizona.edu/doclib/zk/vol181/ZK181_241.pdf.