| Creedite | |
|---|---|
 | |
| General | |
| Category | Halide mineral |
| Formula | Ca3Al2(SO4)(F,OH)10•2(H2O) |
| IMA symbol | Cee[1] |
| Strunz classification | 3.CG.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-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 acalciumaluminiumsulfatefluorohydroxidemineral with formula: Ca3Al2SO4(F,OH)10·2(H2O). Creedite forms colorless to white to purplemonoclinic prismatic crystals. It often occurs as acicular radiating sprays of fine prisms. It is translucent to transparent withindices of refraction of nα = 1.461 nβ = 1.478 nγ = 1.485. It has aMohs hardness of 3.5 to 4 and aspecific gravity of 2.7.
Creedite was first described in 1916 from the Creede Quadrangle inMineral County, Colorado. It is a product of intenseoxidation ofore deposits.
Creedite is a rare hydroxylhalide mineral. Creedite usually forms from theoxidation offluorite 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.[2]
It was later found in other fluorite veins nearTonopah,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 ofSanta Eulalia,Chihuahua,Mexico. It is also found inLa Paz,Bolivia;Pamir Mountains,Tajikistan andDzhezkazgan,Kazakhstan.[4]
Creedite typically occurs with low-grademetamorphic rocks on a fluorite – calcite – quartz matrix or on a sulfide-matrix with its oxidized products. Creedite most commonly found in the form of creedite – carbonate –cyanotrichite –woodwardite –spangolite –kaolinite association. The other less common creedite association is creedite –limonite – kaolinite –hemimorphite –smithsonite –hydrozincite –aurichalcite. Creedite also occurs inskarn formation which usually has association withsulfides, spangolite,brochantite,linarite, limonite,cuprite,wad and kaolinite. In general, creedite usually found as two to three millimeters radialaggregates and less commonly as a single prismatic crystals up to one millimeters long.[5]
Creedite structural composition study was conducted by utilizing 1390 Philips diffractometer with Fe – filtered CoK radiation (λ=1.79021Å), 10–90° 2θ range, peak-height relative intensities. It was concluded that the creedite falls into monoclinic crystal system (2/m) that has space group of C2/c. It was also found that creedite has basal reflections of (2 0 0) and (4 0 0) that are enhanced due to preferred orientation which concur with Michael Fleischer's orientation.[6]
