Crookesite

Selenide of copper, thallium and silver
(repeating unit)Cu
7(Tl, Ag)Se
4IMA symbolCrk[1]Strunz classification2.BD.50Crystal systemTetragonalCrystal classDisphenoidal (4)
H-M symbol: (4)Space groupI4IdentificationColorLead-grayCrystal habitAs finely divided, disseminated specks, and as small veinlets.CleavageGood, two at right anglesFractureBrittleMohs scale hardness2.5–3LusterMetallicDiaphaneityOpaqueSpecific gravity6.90References[2][3]

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

Characteristics

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

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

References

  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
  • 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. S2CID 102058943.
  • Berger, R..A. (1987). "Crookesite and sabatierite in a new light. A crystallographer's comment" (PDF). Zeitschrift für Kristallographie. 181 (1–4): 241–249. Bibcode:1987ZK....181..241B. doi:10.1524/zkri.1987.181.1-4.241.


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