metamorphic
Biotite-rich schist (mica schist)
Mica schist, dominated by biotite mica (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂), with probable quartz and feldspar
AI-generated identification · may be incorrectDark brown-black, strongly foliated, and sparkly from aligned mica flakes; mica has a vitreous-to-pearly luster and perfect basal cleavage. Biotite hardness is about Mohs 2.5–3, while quartz inclusions are about 7; specific gravity commonly 2.7–3.1.
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Physical properties
Dark brown-black, strongly foliated, and sparkly from aligned mica flakes; mica has a vitreous-to-pearly luster and perfect basal cleavage. Biotite hardness is about Mohs 2.5–3, while quartz inclusions are about 7; specific gravity commonly 2.7–3.1.
Formation & geological history
Formed when clay-rich sedimentary rock was subjected to regional metamorphism, causing mica and other minerals to recrystallize and align. Typically Paleozoic or older in West African basement terrains, though exact age cannot be determined from the image.
Uses & applications
Used mainly as decorative stone, specimen material, and occasionally facing or landscaping stone; its pronounced foliation limits structural construction use. Attractive pieces may be collected but are generally inexpensive.
Geological facts
The glitter is natural mica cleavage surfaces, not necessarily metallic mineralization. Individual flakes can split into thin elastic sheets, and the foliation may allow the rock to break into plates.
Field identification & locations
Look for layered planar fabric, abundant reflective brown-black flakes, and easy splitting along foliation. The reported location near 10.1°N, 2.5°W is compatible with schistose rocks of Ghana’s Birimian/West African basement regions; a hand-lens and streak/cleavage tests would improve certainty.
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