igneous
Biotite-bearing granite
Granite, composed mainly of quartz (SiO₂), potassium feldspar, plagioclase, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, light gray to white with black mica clusters; vitreous quartz, pearly mica, and blocky feldspar. Mohs hardness is about 6–7; massive texture, weak cleavage overall, and typical specific gravity of 2.63–2.75.
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Physical properties
Coarse-grained, light gray to white with black mica clusters; vitreous quartz, pearly mica, and blocky feldspar. Mohs hardness is about 6–7; massive texture, weak cleavage overall, and typical specific gravity of 2.63–2.75.
Formation & geological history
A plutonic igneous rock crystallized slowly from silica-rich magma deep in the continental crust, generally during Precambrian to Phanerozoic mountain-building events. The visible crystals indicate slow cooling over thousands to millions of years.
Uses & applications
Widely used as dimension stone, countertops, tiles, monuments, aggregate, and crushed stone; attractive specimens are collected but usually have modest value.
Geological facts
The black minerals are likely biotite, possibly with hornblende or tourmaline; rusty areas commonly reflect weathering of iron-bearing minerals. Granite’s coarse crystals distinguish it from volcanic rhyolite.
Field identification & locations
Common worldwide, especially in continental mountain belts; notable sources include India, Brazil, Scandinavia, Canada, and the United States. Identify it by interlocking visible quartz and feldspar grains with dark mica, rather than layers or foliation.
