igneous
Weathered granite or granitic gneiss
Feldspar–quartz–mica aggregate; likely granite, possibly weakly foliated gneiss
AI-generated identification · may be incorrectCoarse-grained, tan to gray rock with visible feldspar, quartz, and dark biotite/hornblende; vitreous to dull luster, massive or faintly foliated, Mohs hardness about 6–7, with poor cleavage as a whole and density roughly 2.6–2.8 g/cm³.
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Physical properties
Coarse-grained, tan to gray rock with visible feldspar, quartz, and dark biotite/hornblende; vitreous to dull luster, massive or faintly foliated, Mohs hardness about 6–7, with poor cleavage as a whole and density roughly 2.6–2.8 g/cm³.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Mesozoic mountain-building; gneiss forms when comparable material is metamorphosed under high temperature and pressure. Surface weathering has rounded and stained this specimen.
Uses & applications
Used widely as dimension stone, countertops, monuments, aggregate, and building material; attractive polished pieces may be collected, but this specimen appears ordinary.
Geological facts
The pale grains are chiefly feldspar and quartz, while dark grains are likely biotite or amphibole. Iron oxidation commonly produces the tan-brown weathering color.
Field identification & locations
Identify it by interlocking visible crystals and a hard, gritty surface; quartz should resist scratching with a steel knife, while feldspar commonly shows cleavage. Common worldwide in continental crust and exposed mountain terrains.
