igneous
Granite (likely biotite granite or granodiorite)
Coarse-grained plutonic rock composed mainly of quartz, feldspar, and dark mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray, white, and black speckled appearance with granular texture and glassy-to-dull luster. Interlocking crystals are visible, with no obvious layering or cleavage as a whole rock.
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Physical properties
Hardness about 6–7 Mohs; gray, white, and black speckled appearance with granular texture and glassy-to-dull luster. Interlocking crystals are visible, with no obvious layering or cleavage as a whole rock.
Formation & geological history
Formed when silica-rich magma cooled slowly deep underground, allowing large crystals to grow; commonly Paleozoic to Precambrian in exposed continental crust, though age varies by locality.
Uses & applications
Used extensively as dimension stone, countertops, monuments, paving, aggregate, and landscaping rock; attractive polished pieces may be collected but are generally low value.
Geological facts
The specimen’s dark minerals and relatively abundant gray feldspar may indicate granodiorite rather than true granite. Its rounded shape appears naturally weathered or water-worn.
Field identification & locations
Identify it by its coarse interlocking crystals, quartz-rich light areas, and black biotite or amphibole grains; it is common in continental mountain belts and glacial deposits. A fresh streak is typically absent, and it should not fizz with dilute acid.
