igneous
Weathered granite or granitic gneiss fragment
Granite; chiefly quartz (SiO₂), feldspar, and mica, with iron-oxide weathering
AI-generated identification · may be incorrectCoarse, speckled white-gray and brown rock with visible quartz/feldspar grains and rusty staining; hardness about 6–7 Mohs, vitreous to dull luster, granular interlocking texture, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, speckled white-gray and brown rock with visible quartz/feldspar grains and rusty staining; hardness about 6–7 Mohs, vitreous to dull luster, granular interlocking texture, and no obvious cleavage as a whole rock.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in the crust, generally during Precambrian to Phanerozoic continental magmatism; surface weathering altered iron-bearing minerals to brown oxides.
Uses & applications
Common granite is used for crushed aggregate, road stone, building stone, countertops, and monuments; ordinary hand specimens typically have little commercial value.
Geological facts
The brown areas are likely limonite/goethite produced by oxidation rather than the primary rock color. The photograph does not clearly show foliation, so granite is more likely than gneiss.
Field identification & locations
Identify it by hard, interlocking quartz and feldspar grains, pale overall color, and inability to scratch easily with a steel knife; it should not fizz with dilute hydrochloric acid. Common worldwide, especially in continental shields and mountain belts.
