Kermesite
Curated by Maggie Liu · Updated:
Kermesite is a rare antimony oxysulfide that forms cherry-red needle sprays on stibnite, with Xikuangshan in Hunan among its best-known sources.
About Kermesiteextended article
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.
About Kermesite
Kermesite is classified as an oxysulfide mineral in the kermesite group and has the chemical formula Sb2S2O. It crystallizes in the triclinic system and is relatively soft, requiring careful handling. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.
Identification & care
Crystals commonly develop as long acicular to capillary tufts; radiating sprays of deep red needles. Its color is typically cherry red to dark red. The luster is adamantine, the streak is brownish red, and specimens are typically translucent. The cleavage is perfect on {001}. The fracture is uneven, which aids identification.
Collector context
How it forms
The geological setting for Kermesite is typically partial oxidation of stibnite; zone between fresh stibnite and fully oxidized sb minerals. It is commonly found in association with stibnite, senarmonite, valentinite, cervantite, quartz.
Classic Chinese localities
Kermesite has known Chinese occurrences in Hunan.
Why collectors care
Collectors pursue Kermesite for the clarity of its crystal form and, in good material, saturated color that reads instantly across a display case. A well-terminated kermesite on clean matrix photographs well, identifies quickly, and anchors a cabinet piece. Top Chinese specimens over the last two decades have reset the bar for what kermesite looks like at collector grade.
What affects value
Value in Kermesite is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.
Frequently asked questions
What is Kermesite?
Kermesite has the chemical formula Sb2S2O, crystallises in the Triclinic system. Kermesite is a rare antimony oxysulfide that forms cherry-red needle sprays on stibnite, with Xikuangshan in Hunan among its best-known sources.
What is the chemical formula of Kermesite?
The chemical formula of Kermesite is Sb2S2O.
What crystal system does Kermesite belong to?
Kermesite crystallises in the Triclinic crystal system.
Is Kermesite rare?
As a collector mineral, Kermesite is generally considered rare.
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