igneous
Rounded granitic cobble
Granite, composed mainly of quartz, potassium feldspar, plagioclase, and mica
AI-generated identification · may be incorrectCoarse-grained, speckled light gray rock with a granular texture and dull to weakly vitreous luster; hardness about 6–7 Mohs, massive with no prominent cleavage, and typical specific gravity near 2.6–2.7.
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Physical properties
Coarse-grained, speckled light gray rock with a granular texture and dull to weakly vitreous luster; hardness about 6–7 Mohs, massive with no prominent cleavage, and typical specific gravity near 2.6–2.7.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic intrusive events. This specimen was likely rounded by stream transport, glacial abrasion, or weathering.
Uses & applications
Used widely as dimension stone, countertops, paving, monuments, aggregate, and architectural stone; ordinary cobbles have little jewelry value.
Geological facts
Its visible interlocking crystals indicate slow underground cooling rather than volcanic eruption. The rounded shape reflects mechanical erosion after exposure at the surface.
Field identification & locations
Identify it by its coarse interlocking quartz-feldspar-mica grains, light color, and lack of layering or fossils; common in continental mountain belts, glacial deposits, and river gravels. Exact mineral proportions and rock identity require a close examination or thin section.
