Specific gravity: 4.5 to 4.6
Hardness: 1 to 1½
Streak: Brownish red
Kermesite is a secondary mineral that forms as an alteration of
antimony deposits (Webmin).
The oxidation often continues changing kermesite to senarmontite
Associated minerals include stibnite,
At the Lac Nicolet Antimony mine, Saints-Martyrs-Canadiens, Arthabaska RCM, Centre-du-Québec, Quebec, Canada, fine specimens of kermesite have been found with crimson-red to maroon crystals to 5 cm, associated with valentinite, native antimony, quartz and stibnite. The mineralisation is hosted in greenschist facies slate, quartzite, phyllite and serpentinite. Hydrothermal fluids invaded the country rocks and produced the antimony-bearing quartz veins containing the various mineral assemblages (R&M 94.5.444-445).
At the Damingshan Mountain, Shanglin county, Guangxi, China, exceptional kermesite crystals were found in a single pocket, associated with stibnite, valentinite, senarmontite and very rarely pääkkönenite (Minrec 38.1.16).
At the Zhenwei (Zhenxu) antimony-gold deposit, Shanglin county, Guangxi, China, kermesite occurs in the upper oxidation zone, together with cervantite (Minrec 38.1.15-16).
At the type locality, the Neue Hoffnung Gottes Mine, Bräunsdorf, Niederwiesa, Mittelsachsen, Saxony, Germany, kermesite occurs in quartz vein vugs as sprays of small, lustrous red crystals associated with stibnite, berthierite and valentinite (R&M 94.5.442)
At the Krížnica, Pernek, Malacky District, Bratislava Region, Slovakia, antimony mineralisation is associated with shale and phyllite. There were three stages of ore formation, first quartz - pyrite - arsenopyrite, then stibnite - carbonate - quartz, and finally stibnite - kermesite. The kermesite forms dark red radial aggregates to 6 cm together with stibnite, valentinite, senarmontite, schafarzikite and late-stage aragonite and calcite (R&M 94.5.444)
At the Kolársky vrch deposit, Pezinok, Pezinok District, Bratislava Region, Slovakia, kermesite forms excellent radial aggregates of acicular crystals, rarely up to 14 cm, associated with stibnite, valentinite, calcite, and siderite (R&M 94.5.444)
Herichová, Chyžné, Revúca District, Banská Bystrica Region, Slovakia, the first occurrence of kermesite associated with valentinite and jamesonite was found on the stockpile of the old tunnels. Other associated secondary minerals include anglesite, cerussite, gypsum, senarmontite, scorodite and stibiconite. The radial aggregates of kermesite are less than 1 cm across, bright red, and found in quartz vugs to 5 cm across (R&M 94.5.444)
At the Globe and Phoenix mine, Kwekwe, Kwekwe District, Midlands, Zimbabwe, kermesite mineralisation was hosted in quartz veins in talc - carbonate schist and tonalitic gneiss, associated with extensive alteration accompanied by muscovite varieties sericite and fuchsite. The veins occur at the contact between the Kwekwe ultramafic complex and granite gneiss. This mine has produced some of the finest kermesite specimens known outside China (R&M 94.5.440-446).
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