igneous
Quartz-rich granitic rock (likely pegmatitic granite)
Granite/pegmatite; predominantly quartz (SiO₂), feldspar, and dark biotite or amphibole
AI-generated identification · may be incorrectCoarse, interlocking crystals with white to gray quartz and feldspar plus black mineral bands; vitreous quartz luster, no obvious cleavage in quartz, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7.
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Physical properties
Coarse, interlocking crystals with white to gray quartz and feldspar plus black mineral bands; vitreous quartz luster, no obvious cleavage in quartz, Mohs hardness about 6–7, and specific gravity roughly 2.6–2.7.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing large crystals to grow; the specimen is likely Precambrian to Paleozoic or younger depending on its source region. Dark streaks may represent biotite-rich schlieren or a mafic inclusion.
Uses & applications
Used as crushed stone, dimension stone, countertops, monuments, and aggregate; attractive pieces are collected, though this specimen has little jewelry value.
Geological facts
Granite is a rock rather than a single mineral, and its visible crystal size records slow subterranean cooling. Quartz-rich pegmatitic zones can sometimes host tourmaline, beryl, or collectible feldspar crystals.
Field identification & locations
Identify it by its coarse grain, interlocking white/gray quartz-feldspar crystals, and scattered black minerals; it is commonly found in continental crust, stream gravels, and glacial deposits. A streak test, glass-scratching test, and close inspection for cleavage can distinguish quartz from feldspar.
