mineral
Biotite in Host Matrix
Biotite (K(Mg,Fe)3AlSi3O10(F,OH)2)
Hardness: 2.5–3.0 on Mohs scale; Color: Black, dark brown, or dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (sheets); Specific gravity: 2.7–3.3.
- Hardness
- 2
- Color
- Black, dark brown, or dark green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 2.5–3.0 on Mohs scale; Color: Black, dark brown, or dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (sheets); Specific gravity: 2.7–3.3.
Formation & geological history
Formed in igneous or metamorphic environments. Commonly found in granites, pegmatites, schists, and gneisses. It forms from the cooling of magma or the metamorphism of iron-rich sediments.
Uses & applications
Used primarily for its insulating properties in electronics, as a filler in paints and rubber, and as a component in drilling muds. It is also a popular specimen for mineral collectors.
Geological facts
Biotite is a member of the mica group. It is often referred to as 'black mica' and is unique because it can contain significant amounts of iron and magnesium. Individual sheets are flexible and elastic.
Field identification & locations
Identify in the field by its dark color and the ability to flake off thin, flexible, transparent sheets using a pocket knife. Commonly found in areas with exposed igneous or metamorphic basement rocks.
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