igneous
Mica-rich granite or granitic gneiss
Quartz–feldspar–biotite granite; possibly weakly gneissic
AI-generated identification · may be incorrectCoarse, speckled gray-brown specimen with reflective dark biotite mica and pale feldspar/quartz. Typical hardness is about 6–7 Mohs; granular crystalline texture, no obvious cleavage as a whole rock, and specific gravity around 2.6–2.8.
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Physical properties
Coarse, speckled gray-brown specimen with reflective dark biotite mica and pale feldspar/quartz. Typical hardness is about 6–7 Mohs; granular crystalline texture, no obvious cleavage as a whole rock, and specific gravity around 2.6–2.8.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, likely during Precambrian to Phanerozoic continental-crust formation; if foliated, later metamorphic deformation produced granitic gneiss.
Uses & applications
Common granite is used for crushed stone, aggregate, countertops, monuments, and building blocks; small attractive pieces have modest collector interest.
Geological facts
The dark flakes are probably biotite, while translucent gray grains are quartz and cream grains are feldspar. A hand specimen cannot reliably distinguish granite from granitic gneiss without seeing foliation and texture across a larger surface.
Field identification & locations
Look for interlocking visible grains, abundant pale quartz/feldspar, and black mica flakes; it should scratch glass or steel weakly but not be scratched by a knife easily. Common worldwide, especially in continental shields and mountain belts.
