Hercynite
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| Hercynite | |
|---|---|
 | |
| General | |
| Category |
Oxide minerals Spinel group Spinel structural group |
| Formula (repeating unit) | Fe2+Al2O4 |
| Strunz classification | 04.BB.05 |
| Identification | |
| Formula mass | 173.81 |
| Color | Black |
| Crystal habit | Euhedral crystals. Also massive to granular |
| Crystal system | Isometric (4/m 3 2/m) Space Group: F d3m |
| Cleavage | [111] indistinct |
| Fracture | Uneven - flat surfaces (not cleavage) fractured in an uneven pattern. |
| Mohs scale hardness | 7.5 |
| Luster | Vitreous (glassy) |
| Streak | dark green |
| Specific gravity | 3.95 |
| Optical properties | Isotropic |
| Refractive index | n=1.8 |
| Other characteristics | non-radioactive |
| References | [1][2][3] |
Hercynite is a spinel mineral with the formula FeAl2O4.
It occurs in high-grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers.[1]
It was first described in 1847 and its name originates from the Latin name for the Harz, Silva Hercynia, where the species was first found.[1][2]
References
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