Mineral Species: Kermesite

Chemical Formula: Sb2OS2

Chemical Name: Antimony Oxysulphide

Mineral Class: Sulphides

Mineral Notes: Kermesite is a highly unusual sulfide. The formula shows that in addition to antimony and sulphur, there is an oxygen atom standing in for one of the required sulphur atoms. Kermesite is an intermediate oxidation product between the parent Stibnite and ultimate oxidation product Valentinite. Intermediate oxides include Senarmontite and the hydrated sulphide Stibiconite. Usually oxidation of Stibnite preceeds all the way to the latter, but occasionally stops short to form Kermesite. This is fortunate because the mineral forms beautiful violet-red needles. For this reason it has also been called red antimony, purple blende or antimony blende.

Description: Several radiating clusters of sharp needle-like crystals of Kermesite on the surface of a grey matrix. All are very lustrous and have the characteristic deep violet-red colour. One side of the specimen shows very unusual irridescence.

Location: Pezinok, Slovak Republic.