Afwillite Locality: Campomorto Quarry, Pietra Massa Locality, Montalto di Castro, Viterbo Province, Latium, Italy Original description: 1.03 mm group of Afwillite crystals. Collection Domenico Preite photo Matteo Chinellato — Photo: Matteo Chinellato · CC BY-SA 3.0
Afwillite
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.
Intro adapted from Wikipedia (CC BY-SA).
Afwillite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₃[SiO₄][SiO₂(OH)₂]·2H₂O.
It crystallizes in the monoclinic crystal system (space group Cc). It is a member of the Spurrite-Afwillite structural group.
Key properties: Mohs hardness 3–4; specific gravity 2.63; White streak; Vitreous luster; refractive index 1.624; optically biaxial.
IMA symbol Afw, grandfathered status — known before the IMA’s founding, named in 1925.
A product of contact metamorphism of limestones.
It is found associated with Apophyllite, natrolite, thaumasite, merwinite, spurrite, gehlenite, ettringite, portlandite, hillebrandite, foshagite, brucite, calcite.
The mineral was named to honor Alpheus Fuller Williams (1874–1953), General Manager, DeBeers Consolidated Mines, Kimberley, South Africa.