igneous
Granite (likely biotite granite)
Coarse-grained felsic plutonic rock; primarily quartz, plagioclase and potassium feldspar with biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; speckled gray, white and brown-black appearance, granular texture, and generally vitreous-to-dull luster. Interlocking crystals indicate phaneritic structure; cleavage occurs only within constituent feldspars and micas, not as a whole rock.
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Physical properties
Hardness about 6–7 Mohs; speckled gray, white and brown-black appearance, granular texture, and generally vitreous-to-dull luster. Interlocking crystals indicate phaneritic structure; cleavage occurs only within constituent feldspars and micas, not as a whole rock.
Formation & geological history
Formed when silica-rich magma cooled slowly deep within Earth, allowing visible crystals to grow; commonly Precambrian to Mesozoic in age depending on locality. The specimen appears freshly fractured or sawn rather than naturally weathered.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving and aggregate; attractive pieces are collected but are not usually jewelry-grade. Common commercial granite has modest value.
Geological facts
Quartz is typically translucent gray, feldspar is white or pink, and dark biotite or hornblende produces the black-brown flecks. Exact identification may require a hand lens, acid test, or thin-section analysis because similar granitic rocks include granodiorite and tonalite.
Field identification & locations
Common in continental crust and exposed mountain belts worldwide, including North America, Brazil, India and Scandinavia. Identify it by its coarse interlocking grains and lack of layering or foliation; a steel file usually scratches little or not at all.
