Afwillite

Afwillite
Afwillite from Crestmore Quarry, Riverside County, California
General
Category	Nesosilicates
Formula (repeating unit)	Ca3(SiO3OH)2·2H2O
IMA symbol	Afw[1]
Strunz classification	9.AG.75
Crystal system	Monoclinic
Crystal class	Domatic (m) (same H-M symbol)
Space group	Cc
Unit cell	a = 16.278(1), b = 5.6321(4) c = 13.236(1) [Å]; β = 134.9°; Z = 4
Identification
Color	Colorless, white
Crystal habit	Prismatic (striated), tabular, radial fibrous, massive
Cleavage	Perfect along [101], good along [100]
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	3–4
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.630
Optical properties	Biaxial (+)
Refractive index	nα = 1.617 nβ = 1.620 nγ = 1.634
Birefringence	δ = 0.0167
2V angle	Measured: 50° to 56°
Dispersion	r < v
Other characteristics	Piezoelectric
References	[2][3][4]

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.^[4] It occurs in association with apophyllite, natrolite, thaumasite, merwinite, spurrite, gehlenite, ettringite, portlandite, hillebrandite, foshagite, brucite and calcite.^[4]

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.^[3]

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.