igneous
Weathered granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and mica, possibly foliated into gneiss
AI-generated identification · may be incorrectCoarse-grained, mottled gray, pink, white, and black; likely Mohs 6–7, with glassy quartz, blocky feldspar, and dark mica. Massive to weakly banded texture and irregular fracture; exact identification is limited by weathering and the photograph.
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Physical properties
Coarse-grained, mottled gray, pink, white, and black; likely Mohs 6–7, with glassy quartz, blocky feldspar, and dark mica. Massive to weakly banded texture and irregular fracture; exact identification is limited by weathering and the photograph.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, generally during Precambrian to Phanerozoic continental mountain-building. If banded, later metamorphism produced granitic gneiss; the rounded shape reflects transport and weathering.
Uses & applications
Used as crushed aggregate, building stone, monuments, countertops, and landscape stone; attractive polished pieces may be collected but this cobble has little commercial value.
Geological facts
Pink areas are probably potassium feldspar, gray translucent grains quartz, and black flakes biotite or amphibole. Surface staining and abrasion can make granite resemble several other coarse-grained rocks.
Field identification & locations
Identify it by visible interlocking crystals and hardness: quartz and feldspar should resist scratching by a steel knife, while mica may peel into dark flakes. Common in continental shields, mountain belts, glacial deposits, streambeds, and urban landscaping.
