igneous
Rounded granite cobble
Granite; predominantly quartz, alkali feldspar, plagioclase, and mica
AI-generated identification · may be incorrectCoarse-grained, speckled gray-pink rock with a granular texture and likely weakly weathered surface; hardness about 6–7 Mohs, vitreous-to-dull luster, massive structure, and no cleavage as a whole rock. The rounded shape indicates abrasion, likely in a river, glacial deposit, or manually tumbled setting.
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Physical properties
Coarse-grained, speckled gray-pink rock with a granular texture and likely weakly weathered surface; hardness about 6–7 Mohs, vitreous-to-dull luster, massive structure, and no cleavage as a whole rock. The rounded shape indicates abrasion, likely in a river, glacial deposit, or manually tumbled setting.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to Phanerozoic intrusive events; its exact age cannot be determined from the image. Rounding formed later through transport or erosion.
Uses & applications
Used extensively as crushed aggregate, paving stone, building stone, monuments, and countertops; rounded specimens are also used decoratively or as paperweights.
Geological facts
Visible interlocking grains distinguish granite from fine-grained volcanic rocks such as rhyolite. Pink grains are likely potassium feldspar, gray translucent grains quartz, and dark grains biotite or hornblende.
Field identification & locations
Identify it by its coarse interlocking quartz–feldspar texture, pink/gray color, and lack of layering or foliation; common worldwide, especially in exposed continental plutons and glacial or river gravels.
