White acicular and fibrous kottenheimite. Analyzed sample from the Bernd Ternes collection. From: Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Mayen-Koblenz, Rhineland-Palatinate, Germany. — Photo: Leon Hupperichs · CC BY-SA 3.0
Kottenheimite
Kottenheimite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₃Si(SO₄)₂(OH)₆·12H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Ettringite structural group.
Key properties: Mohs hardness 2–2.5; specific gravity 1.92; Vitreous to silky (aggregates) luster; optically uniaxial.
IMA symbol Khm, IMA status: approved, named in 2011.
Found in miarolitic cavities in alkali basalt.
It is found associated with Wollastonite, clinochlore, ellestadite, melilite, cuspidine, and earlier-formed sanidine, clinopyroxene, magnetite.
The name refers to the town near the locality that produced the first specimens.