igneous
Granite pebble
Granite; primarily quartz, alkali feldspar, plagioclase, and dark mica/amphibole
AI-generated identification · may be incorrectCoarse, interlocking grains with mottled gray, white, pink, and black colors; vitreous quartz and feldspar luster, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7.
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Physical properties
Coarse, interlocking grains with mottled gray, white, pink, and black colors; vitreous quartz and feldspar luster, no obvious cleavage as a whole, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7.
Formation & geological history
A plutonic igneous rock crystallized slowly from silica-rich magma deep in Earth’s crust, commonly during Precambrian to Phanerozoic mountain-building events; this rounded specimen was later weathered and transported.
Uses & applications
Used extensively as crushed aggregate, building stone, countertops, monuments, paving, and landscaping; attractive polished pieces have modest decorative and educational value.
Geological facts
The visible speckled texture reflects crystals large enough to grow during slow underground cooling. Dark minerals are likely biotite mica or hornblende, while pale translucent grains are quartz.
Field identification & locations
Identify it by its hard, granular, interlocking texture and mixed light-dark minerals; it commonly occurs in continental mountain belts, glacial deposits, stream gravels, and beaches. A streak test is unhelpful, but quartz scratches glass.
