igneous
Rounded granitic gneiss or granite cobble
Likely biotite granite/granitic gneiss; quartz + feldspar + biotite/hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, gray-and-white, granular texture with weak foliation or weathering; vitreous quartz and feldspar, dark mica/amphibole. Typical hardness ~6–7 Mohs, no obvious cleavage as a whole rock, specific gravity ~2.6–2.8.
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Physical properties
Medium- to coarse-grained, gray-and-white, granular texture with weak foliation or weathering; vitreous quartz and feldspar, dark mica/amphibole. Typical hardness ~6–7 Mohs, no obvious cleavage as a whole rock, specific gravity ~2.6–2.8.
Formation & geological history
Crystallized slowly from silica-rich magma, or represents metamorphosed granite if the faint banding is genuine; commonly Precambrian to Mesozoic, then rounded by river or glacial transport.
Uses & applications
Used as aggregate, dimension stone, paving and landscaping rock; attractive polished pieces are decorative but generally not gemstone material.
Geological facts
The rounded shape indicates substantial abrasion or glacial transport. Distinguishing granite from gneiss requires seeing whether minerals form persistent compositional bands.
Field identification & locations
Identify by interlocking visible quartz and feldspar grains, scattered black biotite/amphibole, and lack of vesicles or sedimentary layering; common worldwide in granitic terrains, streambeds and glacial deposits.
