Osumilite
Osumilite is a very rare potassium-sodium-iron-magnesium-aluminium silicate mineral. Osumilite is part of the milarite group (also known as the milarite-osumilite group) of cyclosilicates.
| Osumilite | |
|---|---|
Osumilite tablets with mullite from Ochtendung, Eifel, Germany. | |
| General | |
| Category | Cyclosilicate |
| Formula (repeating unit) | (K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30 |
| IMA symbol | Osm |
| Strunz classification | 9.CM.05 |
| Dana classification | 63.02.01a.06 |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P6/mcc |
| Unit cell | a = 10.15, c = 14.25 [Å]; Z = 2 |
| Identification | |
| Color | Black, dark blue, dark brown, pink, gray |
| Crystal habit | Crystals tabular to prismatic also anhedral and massive |
| Twinning | Rarely |
| Cleavage | None |
| Fracture | Subconchoidal |
| Mohs scale hardness | 5 - 6 |
| Luster | Vitreous |
| Streak | Blue-gray |
| Diaphaneity | Translucent |
| Specific gravity | 2.62 - 2.64 |
| Optical properties | Uniaxial (+) anomalously biaxial |
| Refractive index | w=1.545-1.547, e=1.549-1.551 |
| Birefringence | 0.004 |
| Pleochroism | Strong |
| References | |
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