igneous
Rounded gray granite or granitic gneiss pebble
Granite; predominantly quartz, feldspar, and mica (exact identification is uncertain from the photograph)
AI-generated identification · may be incorrectMedium- to coarse-grained, gray, speckled, and dull to subtly glassy; typical hardness is about 6–7 Mohs, with no obvious cleavage as a whole and low porosity. Dark spots may be biotite or small weathering pits.
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Physical properties
Medium- to coarse-grained, gray, speckled, and dull to subtly glassy; typical hardness is about 6–7 Mohs, with no obvious cleavage as a whole and low porosity. Dark spots may be biotite or small weathering pits.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events; rounding indicates transport by water, ice, or sediment abrasion. If foliated internally, it may instead be granitic gneiss formed by high-grade metamorphism.
Uses & applications
Commonly used as aggregate, paving stone, riprap, countertops, monuments, and landscaping stone; this small rounded specimen has mainly educational or decorative value.
Geological facts
Its salt-and-pepper appearance reflects interlocking light feldspar/quartz and dark mica or amphibole grains. A fresh broken surface is more diagnostic than the weathered exterior.
Field identification & locations
Look for visible interlocking quartz and feldspar grains, black mica flakes, and resistance to scratching by steel; acid usually produces no reaction. Common worldwide, especially in continental shield and mountain regions.
