igneous
Weathered mica-rich rock fragment
Likely biotite granite or granitic gneiss; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectGray-brown, coarse-grained, sparkly surface with dark mica and pale quartz/feldspar; likely Mohs 6–7 overall, vitreous to pearly luster, with no obvious cleavage as a whole rock. The irregular, crumbly edges suggest weathering.
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Physical properties
Gray-brown, coarse-grained, sparkly surface with dark mica and pale quartz/feldspar; likely Mohs 6–7 overall, vitreous to pearly luster, with no obvious cleavage as a whole rock. The irregular, crumbly edges suggest weathering.
Formation & geological history
Probably formed when silica-rich magma crystallized slowly underground, producing quartz, feldspar, and biotite; if banding or foliation is confirmed, it could instead be metamorphosed granite (gneiss). Such rocks commonly formed hundreds of millions to billions of years ago.
Uses & applications
Granite and gneiss are used for building stone, countertops, aggregate, monuments, and landscaping, but this tiny weathered fragment has no practical or jewelry value.
Geological facts
Quartz is typically glassy and translucent, feldspar is opaque and blocky, and biotite forms dark reflective flakes—useful clues for identification.
Field identification & locations
Look for interlocking visible grains, pale feldspar, gray quartz, and black mica; a streak test is generally unhelpful. Common in continental crust, glacial deposits, stream gravels, and construction fill.
