igneous
Weathered granitic rock, possibly granite or granodiorite
Coarse crystalline quartz–feldspar–mica aggregate; commonly granite/granodiorite
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled gray, tan, and brown with weathering; granular texture and vitreous-to-dull luster. Interlocking quartz and feldspar grains are visible, with minor dark biotite or hornblende; no obvious cleavage as a whole rock.
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Physical properties
Hardness about 6–7 Mohs; mottled gray, tan, and brown with weathering; granular texture and vitreous-to-dull luster. Interlocking quartz and feldspar grains are visible, with minor dark biotite or hornblende; no obvious cleavage as a whole rock.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the continental crust, generally during Precambrian to Phanerozoic plutonic events; surface browning reflects weathering and iron oxidation.
Uses & applications
Widely used as crushed stone, building and monument stone, countertops, paving, and aggregate; this irregular specimen has modest collecting value.
Geological facts
Granite is defined by abundant quartz and alkali feldspar; granodiorite contains relatively more plagioclase. The dark patches may be mafic minerals or weathered inclusions.
Field identification & locations
Identify by its coarse interlocking grains, pale feldspar/quartz, and scattered dark minerals; a glassy streak or acid test can help distinguish it from basalt or quartzite. Common worldwide in continental mountain belts and exposed plutons.
