Dellaite

minerals

kilchoanite

tilleyite

spurrite

Formula: Ca6(Si2O7)(SiO4)(OH)2
Sorosilicate (Si2O7 groups)
Specific gravity: 2.94
Streak: White
Colour: Colourless
Environments

Metamorphic environments
Hydrothermal environments

Localities

At the type locality, Kilchoan, Ardnamurchan, Fort William and Ardnamurchan, Highland, Scotland, UK, dellaite occurs in late-stage, fracture-controlled replacement veins cutting thermally metamorphosed limestone. Associated minerals include calcite, spurrite, kilchoanite, foshagite and tilleyite. The dellaite may have inclusions of calcite (MM 34.1.1-16, HOM).

Alteration

dellaite and calcite to spurrite and H2O
2Ca6(Si2O7)(SiO4)(OH)2 + 3CaCO3 ⇌ 3Ca5(SiO4)2(CO3) + 2H2O
Higher temperatures favour the forward reaction (MM 34.1.1-16).

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