igneous
Quartz-rich granitic cobble
Granite or granitic gneiss; primarily quartz, feldspar, and mica
AI-generated identification · may be incorrectLight gray, coarse-grained, speckled white and black, with a granular texture and vitreous quartz luster; hardness about 6–7 Mohs, no strong cleavage as a whole, and specific gravity roughly 2.6–2.7.
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Physical properties
Light gray, coarse-grained, speckled white and black, with a granular texture and vitreous quartz luster; hardness about 6–7 Mohs, no strong cleavage as a whole, and specific gravity roughly 2.6–2.7.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep underground, likely billions to hundreds of millions of years ago, then exposed and rounded by weathering and stream or beach transport.
Uses & applications
Used as aggregate, landscaping stone, building stone, and decorative cobbles; this ordinary specimen has little jewelry value.
Geological facts
The image shows a mixed gravel bed, so exact identification is limited; the prominent pale cobble may also be weathered granitic gneiss or quartz-bearing metamorphic rock.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, occasional dark mica, and a scratch resistance greater than steel or glass; common in glacial deposits, river gravels, and granitic regions worldwide.
