igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar rock with biotite mica; likely granite, possibly weathered gneiss
AI-generated identification · may be incorrectCoarse, speckled texture with pale pink/tan feldspar, gray quartz, and black biotite; vitreous quartz, dull feldspar, and platy mica. Typical granite hardness is about 6–7 Mohs, with no consistent cleavage as a whole and specific gravity near 2.6–2.7.
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Physical properties
Coarse, speckled texture with pale pink/tan feldspar, gray quartz, and black biotite; vitreous quartz, dull feldspar, and platy mica. Typical granite hardness is about 6–7 Mohs, with no consistent cleavage as a whole and specific gravity near 2.6–2.7.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, generally during Precambrian to Phanerozoic plutonic events; surface weathering has roughened the specimen. If banding or foliation is present, it may instead be metamorphosed granite (gneiss).
Uses & applications
Used widely as dimension stone, countertops, monuments, aggregate, and decorative landscaping material; small specimens have modest collecting interest.
Geological facts
The black flakes are probably biotite, while pink grains are potassium feldspar and translucent grains are quartz. Weathering commonly stains feldspar brown or tan.
Field identification & locations
Identify it by interlocking coarse grains, abundant quartz/feldspar, and shiny black mica flakes; granite commonly occurs in continental mountain belts and shield regions. A fresh broken surface and dilute acid test can help exclude carbonate rocks.
