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Hand Specimen identification: Biotite is distinguished by its association, micaceous nature, and dark color. It may be confused with other micas, especially chlorite. Composition is variable and cannot be determined without detailed ana-lytical work. Chemical Composition : K(Mg,Fe)3(AlSi 3O10)(OH)2 Hardness : 21/2 to 3 Specific Gravity2.9 to 3.1 Cleavage/Fracture : …

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