igneous
Rounded weathered granite (granitoid cobble)
Granite, composed mainly of quartz, feldspar, and mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled gray, tan, brown, and reddish coloration with a dull-to-granular luster. The visible texture is crystalline and massive, without cleavage as a whole; individual feldspar grains may show cleavage.
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Physical properties
Hardness about 6–7 Mohs; mottled gray, tan, brown, and reddish coloration with a dull-to-granular luster. The visible texture is crystalline and massive, without cleavage as a whole; individual feldspar grains may show cleavage.
Formation & geological history
A coarse-grained intrusive igneous rock crystallized slowly from silica-rich magma, commonly during Precambrian to Phanerozoic mountain-building events. Its rounded shape and surface discoloration indicate transport and prolonged weathering, likely in a stream or glacial environment.
Uses & applications
Used extensively as crushed aggregate, building stone, curbing, monuments, countertops, and landscaping material. This rounded specimen has modest decorative or educational value.
Geological facts
Iron oxidation commonly produces the reddish-brown staining seen on weathered granite. Exact identification would be improved by a fresh broken surface or magnification to confirm quartz and feldspar grains.
Field identification & locations
Common worldwide, especially in continental shields and mountain belts; notable sources include New England, the Sierra Nevada, Scandinavia, and India. Look for interlocking visible crystals and a quartz-rich, speckled appearance; it should not fizz with dilute acid.
