igneous
Weathered granite or granitic gneiss
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, brown-gray, granular rock with visible interlocking crystals and weak foliation or weathering. Hardness about 6–7 Mohs; vitreous quartz, feldspathic luster, no obvious cleavage as a whole, and typical specific gravity around 2.6–2.8.
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Physical properties
Coarse-grained, brown-gray, granular rock with visible interlocking crystals and weak foliation or weathering. Hardness about 6–7 Mohs; vitreous quartz, feldspathic luster, no obvious cleavage as a whole, and typical specific gravity around 2.6–2.8.
Formation & geological history
Crystallized slowly from silica-rich magma deep within Earth, commonly during Precambrian to younger continental mountain-building events; the rusty surface reflects oxidation of iron-bearing minerals. If distinct layering is confirmed, it may instead be granitic gneiss, a metamorphic equivalent.
Uses & applications
Commonly used as crushed aggregate, road stone, building stone, monuments, and paving; attractive polished varieties are used for countertops and architectural slabs.
Geological facts
The speckled texture records slow underground cooling, allowing large crystals to grow. Brown coloration commonly develops through surface weathering rather than representing the rock’s fresh interior.
Field identification & locations
Look for visible quartz, pale feldspar, and dark mica or amphibole; granite breaks irregularly and is much harder than sandstone. Common worldwide in continental shields, batholiths, and mountain belts; a fresh broken surface would improve identification.
