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

Crookesite
General
CategorySelenide mineral
Formula
(repeating unit)
Cu
7
(Tl, Ag)Se
4
IMA symbolCrk[1]
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
LusterMetallic
DiaphaneityOpaque
Specific gravity6.90
References[2][3]

Characteristics

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Its chemical formula is reported either as Cu
7
(Tl, Ag)Se
4
or (Cu, Tl, Ag)
2
Se
.[4] 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.[2]

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

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It was discovered in 1866 in Skrikerum, Sweden and named for Sir William Crookes (1832–1919), the discoverer of the element thallium.[2]

See also

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Webmineral site
  3. ^ Handbook of Mineralogy
  4. ^ http://www.mindat.org/min-1159.html Mindat