igneous
Biotite granite or granodiorite
Coarse-grained granitoid composed mainly of quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectHardness about 6–7; gray to brown-speckled, granular texture, vitreous quartz luster, and flaky/reflective biotite. Interlocking crystals are visible, with no obvious foliation or cleavage at the rock scale.
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Physical properties
Hardness about 6–7; gray to brown-speckled, granular texture, vitreous quartz luster, and flaky/reflective biotite. Interlocking crystals are visible, with no obvious foliation or cleavage at the rock scale.
Formation & geological history
Slow cooling of silica-rich magma deep in the crust produced this intrusive igneous rock, typically during Precambrian to Phanerozoic mountain-building events. The rounded shape likely reflects weathering and transport as a cobble.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, countertops, monuments, and decorative material; this ordinary specimen has little jewelry value.
Geological facts
Quartz appears glassy and gray, feldspar is generally white or tan, and biotite creates the dark glittering flakes. Its exact identification between granite and granodiorite requires mineral proportions or thin-section analysis.
Field identification & locations
Common worldwide in continental crust, especially mountain belts and exposed batholiths. Test for glassy quartz, light feldspar, and black mica in a coarse interlocking texture; it should not fizz with dilute acid.
