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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)
Common impurities: Al,Fe,Mg,F
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).
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