Crookesite

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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
LusterMetallic
DiaphaneityOpaque
Specific gravity6.90
References[1][2]

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

Characteristics[edit]

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[edit]

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[edit]

References[edit]

  • Berger, Rolf A.; Sobott, Robert J. (1987). "Characterization of TlCu7S4, a crookesite analogue". Monatshefte für Chemie. 118: 967. doi:10.1007/BF00815324.
  • Berger, R..A. (1987). "Crookesite and sabatierite in a new light A crystallographer's cornrnent" (PDF). Zeitschrift für Kristallographie. 181: 241–249. Bibcode:1987ZK....181..241B. doi:10.1524/zkri.1987.181.1-4.241.