Creedite

Creedite
Creedite, Santa Eulalia District, Municipio de Aquiles Serdán, Chihuahua, Mexico
General
Category	Halide mineral
Formula (repeating unit)	Ca3Al2(SO4)(F,OH)10•2(H2O)
IMA symbol	Cee[1]
Strunz classification	3.CG.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 13.91 Å, b = 8.58 Å, c = 10 Å; β = 94.4°; Z = 4
Identification
Color	Colorless, white, violet, orange
Crystal habit	Generally appears as anhedral to subhedral in matrix; bladelike prismatic and radial, drusy to granular aggregates
Cleavage	Perfect on {100}
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	3.5 - 4
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.71
Optical properties	Biaxial (-)
Refractive index	nα = 1.461 nβ = 1.478 nγ = 1.485
Birefringence	δ = 0.024
2V angle	65°
Dispersion	r > v strong
References	[2][3][4]

Creedite is a calcium aluminium sulfate fluoro hydroxide mineral with formula: Ca₃Al₂SO₄(F,OH)₁₀·2(H₂O). Creedite forms colorless to white to purple monoclinic prismatic crystals. It often occurs as acicular radiating sprays of fine prisms. It is translucent to transparent with indices of refraction of n_α = 1.461 n_β = 1.478 n_γ = 1.485. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 2.7.

Creedite was first described in 1916 from the Creede Quadrangle in Mineral County, Colorado. It is a product of intense oxidation of ore deposits.