igneous
Weathered granite or granitic gneiss
Coarse felsic granitoid, chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectGray-brown, speckled, granular rock with visible light feldspar/quartz and dark mafic minerals; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole. The foliation-like texture may indicate weakly banded gneiss rather than granite.
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Physical properties
Gray-brown, speckled, granular rock with visible light feldspar/quartz and dark mafic minerals; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole. The foliation-like texture may indicate weakly banded gneiss rather than granite.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic continental uplift; gneiss forms when preexisting granite is subjected to high-grade metamorphism. Surface weathering has produced the brown coating and rounded shape.
Uses & applications
Used as crushed aggregate, road stone, building stone, monuments, countertops, and landscaping material; this weathered fragment has little jewelry value.
Geological facts
Quartz is commonly translucent gray, feldspar is white or pink, and biotite/hornblende forms dark flakes or grains. Granite can weather into grus, a sandy material like the surrounding sediment.
Field identification & locations
Identify it by its coarse interlocking grains and three-color mineral mixture; a streak test is ineffective, while quartz scratches glass. Common worldwide in continental crust and exposed plutons.
