igneous
Mica-rich granite or pegmatite fragment
Biotite granite/pegmatite; quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse, uneven interlocking crystals with pale gray-white feldspar or quartz and dark flaky biotite; Mohs hardness about 2.5–7, vitreous to pearly luster, and no uniform cleavage as a whole rock.
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Physical properties
Coarse, uneven interlocking crystals with pale gray-white feldspar or quartz and dark flaky biotite; Mohs hardness about 2.5–7, vitreous to pearly luster, and no uniform cleavage as a whole rock.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma underground, likely during a Precambrian-to-younger plutonic event; the exact age and locality cannot be determined from the photograph.
Uses & applications
Used as dimension stone, aggregate, and decorative material; small attractive pieces are mainly inexpensive teaching or collector specimens.
Geological facts
The dark mineral is probably biotite, which commonly splits into shiny elastic sheets; the pale grains may include both quartz and feldspar, difficult to distinguish at this scale.
Field identification & locations
Look for coarse visible crystals, abundant light quartz/feldspar, and black mica flakes; a glass-scratch test and close inspection of cleavage can help distinguish granite from pegmatite. Common worldwide in exposed intrusive terrains.
