igneous
Biotite granite (weathered granitic rock)
Granite, chiefly quartz–feldspar–biotite; approximate composition SiO₂-rich, with K-feldspar and plagioclase
AI-generated identification · may be incorrectCoarse-grained, interlocking crystals with pale pink/white feldspar, gray translucent quartz, and black platy biotite or amphibole; vitreous quartz, feldspathic luster, Mohs hardness about 6–7, no obvious cleavage as a whole rock, specific gravity roughly 2.6–2.8. Brown-orange areas likely iron-oxide weathering.
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Physical properties
Coarse-grained, interlocking crystals with pale pink/white feldspar, gray translucent quartz, and black platy biotite or amphibole; vitreous quartz, feldspathic luster, Mohs hardness about 6–7, no obvious cleavage as a whole rock, specific gravity roughly 2.6–2.8. Brown-orange areas likely iron-oxide weathering.
Formation & geological history
Slow cooling of silica-rich magma deep in continental crust, producing large crystals; commonly Paleozoic to Precambrian, though granite occurs throughout Earth’s geologic history. Surface weathering oxidizes iron-bearing minerals.
Uses & applications
Widely used as dimension stone, countertops, paving, monuments, aggregate, and building stone; attractive polished pieces have modest lapidary and collecting value.
Geological facts
Granite is an intrusive igneous rock and commonly contains visible quartz and feldspar. Black minerals may weather to rusty brown limonite/goethite.
Field identification & locations
Identify by coarse interlocking grains, abundant light feldspar/quartz, and scattered black mica; unlike gneiss, it lacks clear compositional banding. Common in continental mountain belts and shield regions worldwide.
