Afwillite information

Afwillite
Afwillite
	Afwillite from Crestmore Quarry, Riverside County, California
General
Category	Nesosilicates
Formula; (repeating unit)	Ca3(SiO3OH)2·2H2O
IMA symbol	Afw
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

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.

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ Mindat with location data
^ ^a ^b Webmineral data
^ ^a ^b ^c Handbook of Mineralogy

[1] Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.

[2] Mindat with location data

[Webmin-3] Webmineral data

[HBM-4] Handbook of Mineralogy

Afwillite information

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Afwillite

List of minerals

Portlandite

Ettringite

List of mineral symbols

Brownmillerite

Chlormayenite

Calcium silicate hydrate

Spurrite

Tobermorite

Jennite

Thaumasite

Bultfonteinite

Marianne Straub