metamorphic
Biotite-rich schist (probable)
Mica schist, rich in biotite (K(Mg,Fe)₃AlSi₃O₁₀(OH,F)₂); exact identification is uncertain from the image alone.
AI-generated identification · may be incorrectDark gray-brown with abundant reflective, platy mica grains and pronounced foliation; biotite has Mohs hardness 2.5–3 and perfect basal cleavage. The rock’s overall hardness varies with its quartz and feldspar content.
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Physical properties
Dark gray-brown with abundant reflective, platy mica grains and pronounced foliation; biotite has Mohs hardness 2.5–3 and perfect basal cleavage. The rock’s overall hardness varies with its quartz and feldspar content.
Formation & geological history
Formed when clay-rich sedimentary rock was regionally metamorphosed under heat and pressure, aligning mica into layers; its age depends on the locality and cannot be determined from the photo.
Uses & applications
Used as decorative building stone, facing, and landscaping material; strongly foliated specimens are generally unsuitable for load-bearing uses.
Geological facts
The glinting flakes are likely mica reflecting light from aligned mineral sheets.
Field identification & locations
Look for a sparkly, foliated surface that splits along mica-rich planes; distinguish it from slate by its visible mica grains and sheen. Mica schists occur in metamorphic belts worldwide.
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