igneous
Rounded granitic cobble
Granite or granitic gneiss; primarily quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse granular texture with pale gray-green feldspar/quartz and dark mica or amphibole; Mohs hardness about 6–7, vitreous to dull luster, massive with no obvious cleavage, and specific gravity roughly 2.6–2.8.
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Physical properties
Coarse granular texture with pale gray-green feldspar/quartz and dark mica or amphibole; Mohs hardness about 6–7, vitreous to dull luster, massive with no obvious cleavage, and specific gravity roughly 2.6–2.8.
Formation & geological history
Formed when silica-rich magma crystallized slowly deep underground, likely during an ancient continental mountain-building event; later uplift, erosion, and stream or beach transport rounded it.
Uses & applications
Commonly used as landscaping stone, building aggregate, paving, and decorative cobbles; attractive polished pieces may be sold as inexpensive curios or paperweights.
Geological facts
The smooth oval shape reflects prolonged abrasion in moving water or sediment. The greenish tint may come from altered feldspar, chlorite, epidote, or amphibole.
Field identification & locations
Look for interlocking visible crystals rather than layers or sedimentary grains; a streak test is usually white, and the specimen should resist scratching by a steel knife. Common worldwide in mountain belts, riverbeds, and glacial deposits.
