igneous
Weathered granite or granitic gneiss cobble
Granite; chiefly quartz, feldspar, and mica/amphibole
AI-generated identification · may be incorrectCoarse, mottled gray-brown rock with visible dark and light mineral grains; likely Mohs 6–7, vitreous to dull luster, massive texture, and no obvious cleavage as a whole. The rounded shape indicates stream or glacial abrasion and surface weathering.
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Physical properties
Coarse, mottled gray-brown rock with visible dark and light mineral grains; likely Mohs 6–7, vitreous to dull luster, massive texture, and no obvious cleavage as a whole. The rounded shape indicates stream or glacial abrasion and surface weathering.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in Earth’s crust, commonly during Precambrian to Phanerozoic mountain-building events; gneiss would represent metamorphic recrystallization of similar material. Exact age and identity require a fresh broken surface or laboratory testing.
Uses & applications
Commonly used as crushed aggregate, dimension stone, paving, and decorative landscaping rock; this hand specimen has little commercial value.
Geological facts
The pale grains are likely quartz and feldspar, while dark grains may be biotite mica or hornblende. Iron-bearing minerals commonly produce the brown weathering rind.
Field identification & locations
Look for interlocking crystals, abundant feldspar, glassy gray quartz, and black mica; granite is harder than a steel nail and does not fizz with dilute hydrochloric acid. Common worldwide, especially in continental crust and glacial deposits.
