Cesiodymite
Cesiodymite is an IMA-recognized mineral species in the sulfate class, with the chemical formula CsKCu₅O(SO₄)₅.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Cryptochalcite structural group.
Key properties: Mohs hardness 3; specific gravity 3.593; Pale green streak; Vitreous luster; optically biaxial.
IMA symbol Ced, IMA status: approved, named in 2016.
Occurs as sublimates on basaltic scoria near a volcanic fumarole (>350-400 flC.).
It is found associated with Cryptochalcite, euchlorine, chalcocyanite, dolerophanite, alumoklyuchevskite, anglesite, fedotovite, wulffite, langbeinite, aphthitalite, piypite.
Cesi for the essential cesium content and the Greek δίδυμοζ, which means “a twin brother” in recognition that the mineral is the Cs-K-ordered analogue of cryptochalcite.