igneous
Weathered granitic cobble
Granite to granodiorite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; rounded, fine- to medium-grained texture with pinkish/tan feldspar, gray quartz, and dark minerals. Typically nonfoliated, with vitreous quartz and variable feldspar luster; no obvious cleavage as a whole rock.
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Physical properties
Hardness about 6–7 Mohs; rounded, fine- to medium-grained texture with pinkish/tan feldspar, gray quartz, and dark minerals. Typically nonfoliated, with vitreous quartz and variable feldspar luster; no obvious cleavage as a whole rock.
Formation & geological history
An intrusive igneous rock that crystallized slowly from magma deep in the crust, commonly during Precambrian to younger continental plutonism, then became a rounded stream or glacial cobble through weathering and transport.
Uses & applications
Used as aggregate, road stone, building stone, landscaping rock, and monuments; attractive pieces may be polished for decorative use but this specimen has little commercial value.
Geological facts
The brown surface coloration likely reflects iron-oxide weathering, while the rounded shape indicates abrasion or glacial transport rather than in-place bedrock.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, high hardness, lack of layering, and inability to scratch with a steel knife easily. Common in streambeds, glacial deposits, and granitic terrains worldwide.
