igneous
Weathered granite or granitic gneiss
Granite; chiefly quartz, feldspar, and mica (possibly metamorphosed to gneiss)
AI-generated identification · may be incorrectCoarse, irregularly interlocking grains; mottled gray, cream, black, and reddish-brown, with a dull to slightly granular luster. Hardness is about 6–7 Mohs; cleavage occurs in feldspar, while quartz has none; typical specific gravity is 2.63–2.75.
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Physical properties
Coarse, irregularly interlocking grains; mottled gray, cream, black, and reddish-brown, with a dull to slightly granular luster. Hardness is about 6–7 Mohs; cleavage occurs in feldspar, while quartz has none; typical specific gravity is 2.63–2.75.
Formation & geological history
Formed by slow cooling of silica-rich magma deep underground, commonly during Precambrian to younger continental crust formation; surface weathering rounded the specimen and darkened its fractures.
Uses & applications
Used widely as building stone, countertops, monuments, aggregate, and landscaping rock. This ordinary rounded specimen has little jewelry or commercial value.
Geological facts
The dark areas may be biotite or hornblende, while pink zones are potassium feldspar; reddish staining likely reflects iron-oxide weathering.
Field identification & locations
Common in continental mountain belts and glacial or stream gravels worldwide. A glassy quartz sparkle, visible feldspar crystals, and resistance to scratching by steel support identification; a streak test is usually white.
