igneous
Rounded granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, pale gray rock with dark mafic mineral flecks and scattered pinkish feldspar; typically Mohs 6–7, granular texture, vitreous quartz luster, and no prominent cleavage as a whole. The smooth shape is from abrasion and weathering, not crystal structure.
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Physical properties
Medium- to coarse-grained, pale gray rock with dark mafic mineral flecks and scattered pinkish feldspar; typically Mohs 6–7, granular texture, vitreous quartz luster, and no prominent cleavage as a whole. The smooth shape is from abrasion and weathering, not crystal structure.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust during a Precambrian to Phanerozoic intrusive event, then exposed and rounded by stream, glacial, or shoreline transport. Exact age and whether it is weakly gneissic cannot be confirmed from the image alone.
Uses & applications
Used as dimension stone, crushed aggregate, paving, landscaping, and monuments; attractive polished pieces are occasionally used as decor or specimen material.
Geological facts
Granite commonly shows interlocking crystals visible without magnification and is much harder than limestone. Dark spots are likely biotite or amphibole, while pale grains are feldspar and quartz.
Field identification & locations
Identify it by its speckled crystalline texture, lack of layering, and hardness: it should scratch glass and resist a steel knife. Common worldwide, especially in glaciated regions and stream gravels.
