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Afwillite is a calcium hydroxide nesosilicate mineral with formula Ca3(SiO3OH)2·2H2O. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is between 3 and 4. It occurs as an alteration mineral in contact metamorphism of limestone.〔 It occurs in association with apophyllite, natrolite, thaumasite, merwinite, spurrite, gehlenite, ettringite, portlandite, hillebrandite, foshagite, brucite and calcite.〔 It was first described in 1925 for an occurrence in the Dutoitspan Mine, Kimberley, South Africa and was named for Alpheus Fuller Williams (1874–1953), a past official of the De Beers diamond company.〔 Afwillite is typically found in veins of spurrite and it belongs to the nesosilicate sub-class. It is monoclinic, its space group is P2 and its point group is 2. ==Formation of afwillite== It is suggested that afwillite forms in fractured veins of the mineral spurrite. Jennite, afwillite, oyelite and calcite are all minerals that form in layers within spurrite veins. It appears that the afwillite, as well as the calcite, forms from precipitated fluids. The jennite is actually an alteration of the afwillite, but both formed from calcium silicates through hydration. Laboratory studies determined that afwillite forms at a temperature below 200 °C, usually around 100 °C.〔Kusachi, I, Henmi, C. And Henmi K. (1989) Afwillite and jennite from Fuka, Okayama Prefecture. Japan. Miner J. 14, 279-292.〕 Afwillite and spurrite are formed through contact metamorphism of limestone.〔Barthemy, D. (2000) Afwillite Mineral Data, (http://webmineral.com/data/Afwillite.shtml)〕 Contact metamorphism is caused by the interaction of rock with heat and/or fluids from a nearby crystallizing silicate magma.〔Klein, C. and Dutrow, K. (2007) Manual of Mineral Science. 23rd Edition, 63, 596〕 ===Structure and properties=== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「afwillite」の詳細全文を読む スポンサード リンク
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