igneous
Coarse-grained granite fragment
Granite, typically quartz + alkali feldspar + plagioclase + biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled white/gray with black minerals, granular texture, vitreous quartz and feldspar luster, no obvious cleavage as a whole rock, specific gravity about 2.63–2.75.
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Physical properties
Hardness about 6–7 Mohs; mottled white/gray with black minerals, granular texture, vitreous quartz and feldspar luster, no obvious cleavage as a whole rock, specific gravity about 2.63–2.75.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events; the exact age cannot be determined from the photo.
Uses & applications
Widely used as building stone, countertops, monuments, aggregate, and landscaping rock; attractive hand specimens are collected but usually have modest value.
Geological facts
The visible black grains are likely biotite or hornblende, while translucent gray grains may be quartz; the specimen could also be closely related to granodiorite.
Field identification & locations
Identify it by interlocking visible crystals and a salt-and-pepper appearance; quartz scratches glass, feldspar shows cleavage, and dark mica may split into thin flakes. Common worldwide in continental mountain belts and exposed shields.
