igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar–biotite granite; possibly weakly foliated granitic gneiss
AI-generated identification · may be incorrectCoarse-grained, dark gray-brown rock with visible glittering biotite mica and lighter quartz/feldspar grains; typically Mohs 6–7, vitreous to pearly luster, interlocking crystals, and no obvious cleavage as a whole rock. Exact identification is limited by the uncut surface and image.
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Physical properties
Coarse-grained, dark gray-brown rock with visible glittering biotite mica and lighter quartz/feldspar grains; typically Mohs 6–7, vitreous to pearly luster, interlocking crystals, and no obvious cleavage as a whole rock. Exact identification is limited by the uncut surface and image.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the crust, generally during Precambrian to younger continental mountain-building events; if foliation is confirmed, later metamorphism produced gneissic fabric.
Uses & applications
Common granite is used for crushed stone, aggregate, monuments, countertops, and building facing; attractive specimens may be collected but usually have modest value.
Geological facts
The dark sparkling grains are probably biotite, while translucent gray grains are quartz and pale grains are feldspar. Granite commonly forms large batholiths and resists weathering better than many sedimentary rocks.
Field identification & locations
Look for interlocking visible crystals, abundant quartz/feldspar, and black mica flakes; a streak, fresh broken surface, and hand lens would help distinguish granite from gneiss, diorite, or mica schist. Common worldwide, especially continental shields and mountain belts.
