igneous
Weathered granite (likely with accessory quartz)
Granite; chiefly quartz, K-feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, tan to gray-brown, granular texture with dull to weakly vitreous quartz and feldspar; hardness about 6–7 Mohs, no strong cleavage as a whole, and specific gravity around 2.6–2.7. The image contains several fragments, so exact identification is uncertain.
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Physical properties
Coarse-grained, tan to gray-brown, granular texture with dull to weakly vitreous quartz and feldspar; hardness about 6–7 Mohs, no strong cleavage as a whole, and specific gravity around 2.6–2.7. The image contains several fragments, so exact identification is uncertain.
Formation & geological history
Intrusive felsic magma cooled slowly underground, commonly during Precambrian to Phanerozoic continental mountain-building; surface weathering produced the brown coating. The dark fragment may instead be a mafic metamorphic or igneous rock.
Uses & applications
Used widely as crushed aggregate, dimension stone, countertops, monuments, and architectural cladding; attractive polished pieces are collected but usually have modest value.
Geological facts
Granite’s visible crystals record slow cooling at depth, while iron oxidation commonly creates rusty brown weathering colors. Quartz-rich portions resist weathering better than feldspar.
Field identification & locations
Look for interlocking visible crystals of pink/white feldspar, gray translucent quartz, and black mica or amphibole; a glassy streak or fizzing in dilute acid would suggest something else. Common worldwide, especially in continental shields and mountain belts.
