igneous
Weathered granite or granitic gneiss
Granite; predominantly quartz, feldspar, and mica, possibly altered to gneiss
AI-generated identification · may be incorrectCoarse, mottled gray-tan rock with visible light feldspar/quartz and darker biotite or amphibole; Mohs hardness about 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole.
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Physical properties
Coarse, mottled gray-tan rock with visible light feldspar/quartz and darker biotite or amphibole; Mohs hardness about 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole.
Formation & geological history
Formed by slow cooling of silica-rich magma deep underground, likely hundreds of millions to billions of years old; surface weathering has produced the brown-green staining and rough rind.
Uses & applications
Commonly used as crushed aggregate, dimension stone, paving, monuments, and building material; this ordinary specimen has little jewelry value.
Geological facts
Granite is identified by interlocking visible crystals rather than layers or cemented grains. Green and brown areas may reflect chlorite, epidote, iron oxides, or lichen-related surface staining.
Field identification & locations
Common in continental crust and exposed in places such as the Sierra Nevada, Canadian Shield, New England, and Scandinavian Shield. A fresh broken surface, acid test, and hand lens would help distinguish granite from gneiss or altered volcanic rock.
