Sewardite
Sewardite is a rare arsenate mineral with formula of CaFe3+2(AsO4)2(OH)2. Sewardite was discovered in 1982 and named for the mineralogist, Terry M. Seward (born 1940), a professor of geochemistry in Zürich, Switzerland.
| Sewardite | |
|---|---|
| General | |
| Category | Arsenate minerals |
| Formula (repeating unit) | CaFe2+3(AsO4)2(OH)2 |
| IMA symbol | Sew |
| Strunz classification | 8.BH.30 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Cccm |
| Unit cell | a = 16.461 Å, b = 7.434 Å, c = 12.131 Å; Z = 8 |
| Identification | |
| Formula mass | 464.68 g/mol |
| Color | Dark red, lighter red orange |
| Crystal habit | Platy aggregates, anhedral grains |
| Cleavage | {100} and {011} imperfect |
| Fracture | Splintery – thin elongated fractures |
| Mohs scale hardness | 3.5 |
| Luster | Vitreous (glassy) |
| Streak | Reddish brown |
| Diaphaneity | Translucent |
| Specific gravity | 4.16 |
| Optical properties | Weak Anistropic |
| Refractive index | 1.94 calculated |
| Birefringence | Weak |
| Pleochroism | None |
| References | |
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