igneous
Biotite granite (weathered granitic rock)
Granite, composed mainly of quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled tan-gray rock with visible mica and feldspar; vitreous to pearly luster, interlocking crystals, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.63–2.75.
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Physical properties
Coarse-grained, speckled tan-gray rock with visible mica and feldspar; vitreous to pearly luster, interlocking crystals, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.63–2.75.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events; surface weathering has rounded and stained this specimen.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and building material; attractive hand specimens have modest collector interest.
Geological facts
Granite’s visible grains record slow underground cooling, while its quartz and feldspar resist weathering better than biotite, producing the rough, uneven surface seen here.
Field identification & locations
Identify it by its coarse interlocking grains, pink/white feldspar, gray quartz, and shiny black-brown mica; common worldwide in continental shields and mountain belts. A typical small natural specimen is worth about $2–$15 USD, or $15–$40 if especially fresh, large, or locality-labeled.
