Creedite
| Creedite | |
|---|---|
|
|
| General | |
| Category | Halide mineral |
|
Formula (repeating unit) |
Ca3Al2(SO4)(F,OH)10•2(H2O) |
| 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 | |
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 nα = 1.461 nβ = 1.478 nγ = 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 Creed Quadrangle in Mineral County, Colorado. It is a product of intense oxidation of ore deposits.
Creedite is a rare hydroxylhalide mineral. Creedite usually forms from the oxidation of fluorite ore deposits. Creedite was named after the location where it was discovered in 1916 in the Colorado Fluorspar Co. Mine at Wagon Wheel Gap, located at Creede Quadrangle, Mineral County, Colorado.
It was later found in other fluorite veins near Tonopah, Nye County, Nevada; in the Grand Reef mine, Graham County, Arizona; in the Darwin district, Inyo County, California. It also occurs in the Potosi and other mines of Santa Eulalia, Chihuahua, Mexico. It is also found in La Paz, Bolivia; Pamir Mountains, Tajikistan and Dzhezkazgan, Kazakhstan.
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