igneous
Rounded granitic cobble (weathered granite)
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray-beige, speckled with pink/brown alteration spots, dull to granular luster, and interlocking crystalline texture. Massive, with no obvious cleavage as a whole; approximate specific gravity 2.6–2.7.
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Physical properties
Hardness about 6–7 Mohs; gray-beige, speckled with pink/brown alteration spots, dull to granular luster, and interlocking crystalline texture. Massive, with no obvious cleavage as a whole; approximate specific gravity 2.6–2.7.
Formation & geological history
A coarse-grained intrusive igneous rock crystallized slowly from silica-rich magma, commonly during Precambrian to Phanerozoic continental crust formation. The rounded shape and surface weathering likely result from stream transport or prolonged erosion.
Uses & applications
Used as aggregate, building stone, paving, landscaping cobbles, and monuments; attractive pieces may be collected but are generally low value.
Geological facts
The visible speckling reflects individual feldspar and quartz grains plus iron staining or weathering. Its rounded form is typical of abrasion in rivers or glacial deposits.
Field identification & locations
Identify it by its visible interlocking grains, pale feldspar, translucent/gray quartz, and occasional dark mica or amphibole; it should not fizz with dilute hydrochloric acid. Common worldwide, especially in streambeds and glacial deposits.
