igneous
Weathered granitic rock (likely biotite granite)
Granite; chiefly quartz, potassium feldspar, plagioclase, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, light gray to white with dark biotite-rich patches; vitreous quartz and feldspar luster, interlocking crystals, no strong cleavage as a whole. Typical hardness is about 6–7 Mohs and specific gravity about 2.6–2.7.
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Physical properties
Coarse-grained, light gray to white with dark biotite-rich patches; vitreous quartz and feldspar luster, interlocking crystals, no strong cleavage as a whole. Typical hardness is about 6–7 Mohs and specific gravity about 2.6–2.7.
Formation & geological history
An intrusive felsic igneous rock formed by slow cooling of silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events. The dark surface patterns reflect weathering, mineral segregation, or lichen staining.
Uses & applications
Used widely as dimension stone, countertops, monuments, aggregate, and building facades; attractive polished pieces may be decorative but this specimen is not gem-grade.
Geological facts
Granite’s visible crystals indicate slow underground cooling. Biotite and iron-bearing minerals commonly weather to brown stains and may create dark mottling.
Field identification & locations
Identify it by its coarse interlocking quartz–feldspar–mica texture and lack of layering or vesicles; a hand lens helps confirm glassy quartz and flaky biotite. Common worldwide in continental crust and exposed plutons.
