Afwillite

tilleyite

gehlenite

Formula: Ca3[SiO4][SiO2(OH)2].2H2O
Nesosilicate (insular SiO4 groups)
Specific gravity: 2.630
Hardness: 3 to 4
Streak: White
Colour: Colourless, white
Solubility: Gelatinises in hydrochloric or sulphuric acid (Dana)
Environments

Metamorphic environments

Afwillite occurs in the contact zone of eruptive rocks with sedimentary rocks, and in xenoliths of sedimentary rocks in volcanic rocks, also in carbonate hornfels and in stratabound manganese deposits. It may form from tilleyite (Dana). Associated minerals include apophyllite, natrolite, thaumasite, merwinite, spurrite, gehlenite, ettringite, portlandite, hillebrandite, foshagite, brucite and calcite (HOM).

At Viterbo, Italy, afwillite is associated with tobermorite, calcite and ettringite. A hydrothermal mineral (Dana).

At the type locality, the Dutoitspan Mine, Kimberley, Francis Baard District, Northern Cape, South Africa, afwillite has been found in a large dolerite inclusion in the kimberlite, associated with apophyllite, calcite and natrolite in crystals up to 11 cm in length (AM10.447-448, R&M 91.4.366). It may form from spurrite (Dana).

At Crestmore, San Bernadino county, California, USA, afwillite occurs in fractures associated with quartz, thaumasite, merwinite, gehlenite and calcite (Dana).

Common impurities: Al,Fe,Mg,F

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