Okenite

Okenite (CaSi₂O₅·2H₂O)[2] is a silicate mineral that is usually associated with zeolites. It most commonly is found as small white "cotton ball" formations within basalt geodes. These formations are clusters of straight, radiating, fibrous crystals that are both bendable and fragile.[4] It also belongs to the family of the calcium silicate hydrates (C-S-H) commonly found in hardened cement paste. In cement chemist notation (CCN) it is noted as CaO·2SiO₂·2H₂O and abbreviated as CS₂H₂.

Okenite
General
Category	Phyllosilicate
Formula (repeating unit)	CaSi2O5·2H2O
Strunz classification	9.EA.40
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 9.69, b = 7.28 c = 22.02 [Å]; α = 92.7° β = 100.1°, γ = 110.9°; Z = 2
Identification
Color	White, may show slightly yellow or blue tint
Crystal habit	Bladed crystals, typically fibrous, clusters of curved crystals and radial balls
Twinning	Lamellar
Cleavage	Perfect on {001}
Fracture	Splintery
Tenacity	Elastic
Mohs scale hardness	​4 ^1⁄2-5
Luster	Vitreous, pearly
Streak	White
Diaphaneity	Transparent, translucent
Specific gravity	2.28 - 2.33
Optical properties	Biaxial (-)
Refractive index	nα = 1.512 - 1.532 nβ = 1.514 - 1.535 nγ = 1.515 - 1.542
Birefringence	δ = 0.003 - 0.010
2V angle	Measured: 60°
References	[1][2][3]

Discovery and occurrence

It was first described in 1828 for an occurrence at Disko Island, Greenland and named for German naturalist Lorenz Oken (1779–1851).[3]

Minerals associated with okenite include apophyllite, gyrolite, prehnite, chalcedony, goosecreekite and many of the mother zeolites. Okenite is found in India, mainly within the state of Maharashtra. Other localities include Bulla Island, Azerbaijan; Aranga, New Zealand; Chile; Ireland and Bordo Island in the Faroe Islands.[2]

References

1. Okenite in the Handbook of Mineralogy
2. Okenite on Mindat.org
3. Okenite data on Webmineral
4. "Okenite (Hydrated Calcium Silicate Hydroxide)". Galleries.com. Retrieved 2013-07-27.