Green chlorothionite from the Vesuvius volcano (Vesuvius Fumaroles, Mount Vesuvius, Naples Province, Campania, Italy). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Chlorothionite
Chlorothionite is an IMA-recognized mineral species in the sulfate class, with the chemical formula K₂Cu(SO₄)Cl₂.
It crystallizes in the orthorhombic crystal system (space group Pnma). It is a member of the Chlorothionite structural group.
Key properties: Mohs hardness 2.5; specific gravity 2.69; optically biaxial.
IMA symbol Ctn, grandfathered status — known before the IMA’s founding, named in 1872.
Occurs as sublimates around volcanic fumaroles.
Its name comes from the Greek for chlorine and sulfur in the composition.
Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet.
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