igneous
Weathered granitic pebble
Granite, likely biotite–feldspar–quartz granite or granodiorite
AI-generated identification · may be incorrectMedium- to coarse-grained, speckled cream/tan, gray, and black; vitreous to dull luster and interlocking crystals. Hardness is approximately 6–7 Mohs; quartz has no cleavage, feldspar shows two cleavages, and specific gravity is about 2.63–2.75.
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Physical properties
Medium- to coarse-grained, speckled cream/tan, gray, and black; vitreous to dull luster and interlocking crystals. Hardness is approximately 6–7 Mohs; quartz has no cleavage, feldspar shows two cleavages, and specific gravity is about 2.63–2.75.
Formation & geological history
Slow cooling of silica-rich magma deep within continental crust produced the crystalline texture; subsequent uplift and erosion rounded it into a pebble. Such plutonic rocks commonly formed during Precambrian to Phanerozoic mountain-building events.
Uses & applications
Crushed granite is widely used for aggregate, road base, concrete, and building stone; attractive pieces are used for landscaping and lapidary specimens, though this rounded pebble has little gem value.
Geological facts
The black grains are likely biotite or hornblende, the pale grains are feldspar, and any translucent gray grains are quartz. Its granular “salt-and-pepper” appearance distinguishes it from volcanic rocks that cool too quickly to form visible crystals.
Field identification & locations
Common in streambeds, glacial deposits, and eroded mountain terrains worldwide. A glassy quartz scratch, lack of layering or foliation, and visible interlocking grains support identification; a precise name requires thin-section or chemical analysis.
