igneous
Coarse-grained granite or granitic gneiss
Granite (quartz–feldspar–mica aggregate), possibly gneiss if foliation is present
AI-generated identification · may be incorrectLight gray, speckled white and dark minerals with a coarse crystalline texture; likely quartz, feldspar, and biotite/hornblende. Hardness is approximately 6–7 Mohs, nonmetallic luster, granular crystal structure, and no obvious cleavage as a whole rock.
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Physical properties
Light gray, speckled white and dark minerals with a coarse crystalline texture; likely quartz, feldspar, and biotite/hornblende. Hardness is approximately 6–7 Mohs, nonmetallic luster, granular crystal structure, and no obvious cleavage as a whole rock.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, commonly during Precambrian to younger continental mountain-building events; gneiss forms when such rocks undergo high-grade metamorphism and recrystallization.
Uses & applications
Used as dimension stone, countertops, monuments, paving, aggregate, and landscaping material; attractive hand specimens have modest collecting value.
Geological facts
The visible interlocking grains indicate slow cooling rather than volcanic eruption. Dark minerals are commonly biotite mica or amphibole, while translucent grains are quartz.
Field identification & locations
Identify it by coarse interlocking grains, abundant pale feldspar/quartz, and scattered dark mica or amphibole; foliation or banding would favor gneiss. Common worldwide in continental crust and exposed mountain belts.
