igneous
Weathered granite or granitic gneiss
Granite–gneiss; chiefly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, pale cream to gray with dark biotite/hornblende patches; typically vitreous to pearly luster, interlocking crystals, no cleavage as a whole, Mohs hardness about 6–7, and specific gravity 2.6–2.8. The image is low-resolution, so exact identification is limited.
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Physical properties
Coarse-grained, pale cream to gray with dark biotite/hornblende patches; typically vitreous to pearly luster, interlocking crystals, no cleavage as a whole, Mohs hardness about 6–7, and specific gravity 2.6–2.8. The image is low-resolution, so exact identification is limited.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground; gneiss forms when granite is subjected to intense heat and pressure, often during mountain building. Common specimens are Precambrian to Phanerozoic in age.
Uses & applications
Widely used as crushed stone, aggregate, curbing, monuments, countertops, and architectural facing; attractive polished pieces are also collected.
Geological facts
Quartz appears gray or translucent, feldspar is white or cream, and mica or amphibole creates the dark flecks. Gneiss commonly shows compositional banding, whereas granite has a more randomly speckled texture.
Field identification & locations
Look for visible interlocking quartz and feldspar grains, dark mica/amphibole, and a very hard, non-porous surface; it should scratch glass but not be scratched by a steel knife. Common worldwide, especially in continental shield and mountain regions.
