mineral
Likely brown mica (biotite) specimen
Biotite, a potassium-iron-magnesium sheet silicate; approximate formula K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂
AI-generated identification · may be incorrectBrown to bronze, with a vitreous-to-pearly luster and prominent sheet-like cleavage; biotite has Mohs hardness about 2.5–3 and a monoclinic crystal structure. The photo does not show enough detail for definitive identification.
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Physical properties
Brown to bronze, with a vitreous-to-pearly luster and prominent sheet-like cleavage; biotite has Mohs hardness about 2.5–3 and a monoclinic crystal structure. The photo does not show enough detail for definitive identification.
Formation & geological history
Biotite crystallizes in many igneous and metamorphic rocks as magma cools or during metamorphism. It occurs in rocks spanning a wide range of geological ages.
Uses & applications
Commonly studied as a rock-forming mineral and used in geological research; mica has limited industrial use as an insulating and filler material. This rough specimen has little jewelry value.
Geological facts
Mica minerals split into thin, flexible sheets; biotite’s iron-rich composition gives it darker colors than muscovite.
Field identification & locations
Look for brown, platy layers that peel into sheets and reflect light. Common in granite, schist, and gneiss worldwide; the specimen’s identity is uncertain from this view.
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