igneous
Granite pebble
Granite; chiefly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, speckled white-gray rock with glassy quartz, pale feldspar, and dark biotite or amphibole; Mohs hardness about 6–7, generally nonfoliated, with poor cleavage as a whole and granular texture.
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Physical properties
Coarse-grained, speckled white-gray rock with glassy quartz, pale feldspar, and dark biotite or amphibole; Mohs hardness about 6–7, generally nonfoliated, with poor cleavage as a whole and granular texture.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Mesozoic mountain-building events; this specimen was likely rounded by stream or beach transport.
Uses & applications
Used as crushed aggregate, dimension stone, countertops, monuments, and landscaping material; ordinary pebbles have little commercial value.
Geological facts
The interlocking crystals indicate slow underground cooling, unlike volcanic rhyolite, which is usually fine-grained. Weathering commonly releases resistant quartz and feldspar grains into sand.
Field identification & locations
Identify it by its visibly interlocking quartz-feldspar-mica grains and pink, white, gray, or black speckling; common worldwide in continental crust and gravel deposits. A hand lens and streak, hardness, or acid tests can refine identification.
