What is Kermesite?
Kermesite is a striking antimony oxysulfide known for cherry-red fibrous sprays and its place in oxidised antimony ore assemblages.
Mineralogy and crystal structure
Reference formula: Sb2S2O. Kermesite has a triclinic antimony oxysulfide structure and commonly occurs as a surface alteration product of stibnite. Its soft fibres and antimony content require careful display and handling. Kermesite is classified with sulfides and has a triclinic crystal system. Typical hardness is 1–1.5 on the Mohs scale and specific gravity is approximately 4.5–4.7.
Colour, lustre and habit
Typical colours include cherry-red, red-brown, black. The usual acicular, fibrous, radiating habit and metallic, sub-metallic, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kermesite forms in or is associated with oxidised zones of stibnite-rich hydrothermal deposits. Important documented localities include Germany, Slovakia, Romania, China, Mexico and the United States.
A red metallic spray with cabinet presence
Kermesite is one of the most visually distinctive antimony minerals: its red fibres can look almost organic against dark matrix. It is a high-impact specimen for collectors who value unusual habits and strong colour contrast.
Collecting and care
Antimony-bearing and very soft: keep sealed from dust, avoid touching fibrous sprays and do not cut or grind.
