Corkite
Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. Corkite is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite.
| Corkite | |
|---|---|
Corkite on a goethite matrix | |
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | PbFe3[(OH)6:SO4:PO4] |
| IMA symbol | Cok |
| Strunz classification | 8.BL.05 |
| Dana classification | 43.4.1.2 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3/m) (same H-M symbol) |
| Space group | R3m |
| Unit cell | a = 7.3065(5) Å, c = 16.897(2) Å; V = 781.2 ų; Z = 3 |
| Identification | |
| Formula mass | 667.82 g/mol |
| Color | Brown to light yellowish brown, pale yellow, yellowish green to dark green |
| Crystal habit | Crystals pseudocubic rhombohedral with prominent {1011}. Commonly in crusts and massive |
| Cleavage | Perfect on {0001} |
| Mohs scale hardness | 3.5–4.5 |
| Luster | Vitreous, resinous |
| Diaphaneity | transparent |
| Specific gravity | 4.295 (measured), 4.31 (calculated) |
| Optical properties | Uniaxial (−), may appear anomalously biaxial |
| Refractive index | nω = 1.930 nε = 1.930 n = 1.93 – 1.96 |
| Birefringence | δ = 0.000 |
| Other characteristics | Readily soluble in warm HCl |
| References | |
Corkite is named after County Cork, Ireland; the location where the first notable amount was discovered in 1869. Like many of the other minerals in the beudantite group, corkite is a relatively uncommon, secondary mineral that occurs in oxidation zones near hydrothermal base metal deposits. It occurs associated with pyromorphite, malachite, plumbojarosite, limonite and quartz.
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