White crystal aggregates of kilchoanite in a matrix of purple spurrite. From Fuka Mine, Bitchu-cho, Takahashi, Honshu Island, Japan. — Photo: David Hospital · CC BY-SA 4.0
Kilchoanite
Kilchoanite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₆(SiO₄)(Si₃O₁₀).
It crystallizes in the orthorhombic crystal system (space group I2cm).
Key properties: specific gravity 2.992; optically biaxial.
IMA symbol Ki, grandfathered status — known before the IMA’s founding, named in 1961.
Found in limestones thermally metamorphosed by invasion of gabbro; thought to have developed during retrograde metamorphism following decarbonation of limestone and thus under low pressure of CO2 (Kilchoan, Scotland; Carlingford, Ireland).
It is found associated with Rankinite, spurrite, tilleyite, melilite, cuspidine, grossular, wollastonite, vesuvianite (Kilchoan, Scotland); rankinite, larnite, spurrite (Golden Gully.
The name refers to Kilchoan, Scotland, where it was first found.