Crookesite

Crookesite is a selenide mineral composed of copper and selenium with variable thallium and silver. Its chemical formula is reported either as Cu₇(Tl,Ag)Se₄ or (Cu,Tl,Ag)₂Se. It is formed by precipitation from hydrothermal fluids.

Additional recommended knowledge

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Essential Laboratory Skills Guide

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.

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

References

• Webmineral site
• Mindat mineral data with locations