igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar–biotite rock; commonly granite (quartz + K-feldspar/plagioclase + biotite)
AI-generated identification · may be incorrectCoarse-grained, speckled white/gray and black with prominent platy, reflective biotite mica; quartz is glassy and feldspar is pale. Typical hardness is 6–7 overall; mica has perfect basal cleavage, and granite density is about 2.6–2.7 g/cm³.
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Physical properties
Coarse-grained, speckled white/gray and black with prominent platy, reflective biotite mica; quartz is glassy and feldspar is pale. Typical hardness is 6–7 overall; mica has perfect basal cleavage, and granite density is about 2.6–2.7 g/cm³.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, producing interlocking crystals; comparable granites formed throughout the Precambrian and Phanerozoic. If the minerals show strong alignment or banding, it may instead be metamorphosed granitic gneiss.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and building material; attractive polished pieces are collected but are usually modestly valuable.
Geological facts
The black flakes are biotite, whose perfect cleavage lets it split into elastic sheets. White translucent grains are generally quartz, while opaque-to-pale blocky grains are feldspar.
Field identification & locations
Identify it by its coarse interlocking texture, abundant quartz/feldspar, and shiny black mica; it is common in continental mountain belts worldwide. A hand lens, streak test, and fresh unweathered surface help distinguish it from mica-rich schist.
