igneous
Weathered granite or granitic gneiss
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, mottled gray-brown rock with pale feldspar/quartz and dark mafic minerals; typical hardness is about 6–7 Mohs, vitreous to dull luster, and no prominent cleavage as a whole. The apparent brown surface likely reflects iron-oxide weathering.
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Physical properties
Coarse-grained, mottled gray-brown rock with pale feldspar/quartz and dark mafic minerals; typical hardness is about 6–7 Mohs, vitreous to dull luster, and no prominent cleavage as a whole. The apparent brown surface likely reflects iron-oxide weathering.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to Phanerozoic mountain-building events; the image may also show weakly foliated granitic gneiss. Uplift and weathering exposed the specimen.
Uses & applications
Used as crushed aggregate, building stone, monuments, countertops, and landscaping material; ordinary hand specimens have little jewelry value.
Geological facts
Quartz appears glassy or gray, feldspar is blocky and pale, and dark biotite or hornblende forms flakes or grains. Gneissic specimens show compositional banding, while granite is generally massive and speckled.
Field identification & locations
Common worldwide in continental mountain belts, including the Sierra Nevada, Canadian Shield, Appalachians, and Scandinavia. Check for interlocking visible grains, feldspar cleavage, and a streakless surface; a definitive identification may require a fresh break or thin section.
