igneous
Rounded granite or granitic gneiss cobble
Granitoid, chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, pale gray-tan, granular texture with subdued vitreous grains; typically Mohs 6–7, nonmetallic luster, interlocking crystals, and no obvious cleavage as a whole. Its smooth oval shape reflects abrasion rather than crystal form.
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Physical properties
Medium- to coarse-grained, pale gray-tan, granular texture with subdued vitreous grains; typically Mohs 6–7, nonmetallic luster, interlocking crystals, and no obvious cleavage as a whole. Its smooth oval shape reflects abrasion rather than crystal form.
Formation & geological history
Likely an ice- or water-rounded glacial/stream cobble formed from slowly cooled intrusive magma, commonly Precambrian to Paleozoic in age depending on source terrain. Exact identification requires a fresh broken surface or hand-lens examination.
Uses & applications
Used as landscaping stone, riprap, aggregate, and decorative cobbles; attractive pieces may be collected but are generally not gem material.
Geological facts
Granite commonly contains visible quartz and feldspar, while gneiss shows compositional banding; this specimen appears too weathered and uniformly rounded to distinguish them confidently.
Field identification & locations
Look for translucent gray quartz, white or pink feldspar, and black mica or amphibole; a streak test is usually white, and it will not fizz with dilute hydrochloric acid. Common around glacial deposits, riverbeds, and eroded granite terrains.
