Kermesite

Kermesite is what happens when the world’s most dramatic antimony mineral starts to rust. An oxysulfide with the formula Sb₂S₂O, it forms at the very first stage of stibnite’s oxidation — nature caught mid-transformation — and it announces itself in a color no other antimony mineral can offer: deep cherry red.

The Chinese angle

The Xikuangshan deposit near Lengshuijiang, Hunan, is the world’s largest antimony resource and one of kermesite’s benchmark modern sources. Sprays of flexible red needles perched on steel-grey stibnite blades make combination specimens with color contrast few sulfide-suite pieces can match. For collectors of Chinese minerals, a good kermesite completes the antimony story that stibnite begins.

Identification

The habit is distinctive: radiating tufts and fans of slender needles, cherry-red to violet-red, with an adamantine to semi-metallic gleam and a brownish-red streak. It is soft and the needles are fragile — dings and matted sprays significantly affect value, so condition should be examined closely.

Collecting notes

Because kermesite grows on stibnite, judge both parts of the specimen: the stibnite base should be lustrous and undamaged, and the red sprays should stand proud rather than lie crushed. Classic European material from Pezinok in Slovakia set the historical standard; Chinese pieces from the Hunan antimony belt are the accessible modern alternative. Keep specimens dry and out of strong light, as with the rest of the antimony suite.