igneous
Polished granite pebble
Granite, commonly quartz–feldspar–mica aggregate
AI-generated identification · may be incorrectHardness about 6–7 Mohs; rounded and polished, with mottled black, gray, white, and pink grains, granular texture, and generally vitreous to dull luster. Interlocking crystals show no obvious cleavage as a whole rock; specific gravity is about 2.6–2.8.
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Physical properties
Hardness about 6–7 Mohs; rounded and polished, with mottled black, gray, white, and pink grains, granular texture, and generally vitreous to dull luster. Interlocking crystals show no obvious cleavage as a whole rock; specific gravity is about 2.6–2.8.
Formation & geological history
Slow cooling of silica-rich magma deep in the continental crust produced coarse crystals, typically during Precambrian to younger continental magmatism; the specimen was later weathered, rounded, and polished.
Uses & applications
Used as decorative stone, countertops, monuments, aggregate, landscaping material, and inexpensive craft or display pieces.
Geological facts
The dark grains are likely biotite, hornblende, or other mafic minerals, while lighter grains are feldspar and quartz. Exact identification would require a fresh surface or microscope.
Field identification & locations
Recognize granite by its coarse, speckled interlocking grains and inability to scratch glass easily; common sources include continental mountain belts and glacial or river gravels. A polished surface can obscure texture.
