Weddellite
Weddellite (CaC2O4·2H2O) is a mineral form of calcium oxalate named for occurrences of millimeter-sized crystals found in bottom sediments of the Weddell Sea, off Antarctica. Occasionally, weddellite partially dehydrates to whewellite, forming excellent pseudomorphs of grainy whewellite after weddellite's short tetragonal dipyramids. It was first described in 1936 but only named in 1942.
| Weddellite | |
|---|---|
| General | |
| Category | Oxalate minerals |
| Formula (repeating unit) | CaC2O4·2H2O |
| IMA symbol | Wed |
| Strunz classification | 10.AB.40 |
| Crystal system | Tetragonal |
| Crystal class | Dipyramidal (4/m) H-M symbol: (4/m) |
| Space group | I4/m |
| Unit cell | a = 12.371, c = 7.357 [Å]; Z = 8 |
| Identification | |
| Color | Colorless to white, may be yellowish brown to brown from impurities |
| Crystal habit | Isolated crystals, may be corroded |
| Twinning | Single or multiple |
| Cleavage | Good on {010} |
| Fracture | Conchoidal |
| Mohs scale hardness | 4 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 1.94 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.523 nε = 1.544 |
| Birefringence | δ = 0.021 |
| Other characteristics | Dehydrates on air exposure |
| References | |
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