Kilchoanite

kilchoanite

spurrite

tilleyite

cuspidine

Images

Formula: Ca₆(SiO₄)(Si₃O₁₀)
Sorosilicate (Si₂O₇ groups), paramorph of rankinite
Crystal System: Orthorhombic
Specific gravity: 2.992 measured, 3.00 calculated
Streak: White
Colour: Colourless
Common impurities: Fe,Al
Environments

Metamorphic environments

Localities

At Golden Gully, New Zealand, kilchoanite has been found associated with rankinite, larnite and spurrite (HOM).

At the type locality, Kilchoan, Ardnamurchan, Highland, Scotland, UK, kilchoanite was formed by retrograde high temperature contact metamorphism of siliceous limestone (Mindat, Dana) intruded by gabbro. Kilchoanite is associated with rankinite, which it replaces, spurrite, tilleyite, melilite, cuspidine, grossular, wollastonite and vesuvianite (AM 46.1203, HOM).

Alteration

kilchoanite to rankinite
Ca₆(SiO₄)(Si₃O₁₀) ⇌ 2Ca₃Si₂O₇
Higher temperatures favour the forward reaction (MM 34.1.1-16).

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