Ottrelite is a form of chloritoid. Its empirical formula is (Mn,Fe,Mg)2Al4Si2O10(OH)4.
| Ottrelite |
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 Ottrelite |
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| Category | Nesosilicate |
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Formula
(repeating unit) | (Mn,Fe,Mg)2Al4Si2O10(OH)4 |
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| Strunz classification | 09.AF.85 |
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| Formula mass | 490.11 |
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| Color | Pistachio green |
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| Crystal habit | Granular |
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| Twinning | Polysynthetic, {001} |
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| Cleavage | {001} perfect; {110} likely |
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| Mohs scale hardness | 6-7 |
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| Luster | Vitreous to nearly adamantine on cleavages |
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| Streak | Greenish, grayish |
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| Diaphaneity | Translucent |
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| Specific gravity | 3.50 |
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| Density | 3.52 |
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| Dispersion | r > v, strong |
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| References | [1][2][3] |
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