Alleghanyite
| Alleghanyite | |
|---|---|
Alleghanyite crystals up to 2 mm in size in a mixed franklinite/calcite/willemite block of 11×6.5×4 cm size. Location: Sterling Mine, Sussex County, New Jersey, US.
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| General | |
| Category |
Nesosilicates Humite group |
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Formula (repeating unit) |
Mn5(SiO4)2(OH)2 |
| Strunz classification | 9.AF.45 |
| Dana classification | 52.3.2b.1 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/a |
| Unit cell | a = 10.46, b = 4.86 c = 8.3 [Å]; β = 109.133°; Z = 2 |
| Identification | |
| Formula mass | 492.87 g/mol |
| Color | Brown, bright pink, grayish pink, white |
| Crystal habit | Granular; anhedral to subhedral crystals in matrix |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 4 (meas.), 4.11 (calc.) |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.756 nβ = 1.78 nγ = 1.792 |
| Birefringence | 0.036 |
| 2V angle | 72° (meas.), 68° (calc.) |
| Other characteristics | Non-fluorescent |
| References | |
Alleghanyite is a moderately rare humite mineral with formula Mn5(SiO4)2(OH)2, belonging to the nesosilicates class. In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.
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