igneous
Pegmatitic granite (quartz–feldspar–mica rock)
Granitic pegmatite, composed chiefly of quartz (SiO₂), feldspars, and dark mica, likely biotite
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals; pinkish feldspar, translucent gray quartz, and dark mica are visible. Hardness is about 6–7 Mohs; luster ranges from glassy on quartz to pearly on mica, with no consistent cleavage across the whole rock.
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Physical properties
Coarse, irregular interlocking crystals; pinkish feldspar, translucent gray quartz, and dark mica are visible. Hardness is about 6–7 Mohs; luster ranges from glassy on quartz to pearly on mica, with no consistent cleavage across the whole rock.
Formation & geological history
Crystallized slowly from silica-rich magma, commonly in late-stage veins and dikes within older continental crust. Pegmatites formed throughout geologic time; this specimen’s age cannot be determined from the image.
Uses & applications
Granite and pegmatite are used as decorative and building stone; quartz and feldspar have industrial uses, while attractive crystals may be collected.
Geological facts
Pegmatites can contain exceptionally large crystals and, in some localities, valuable lithium-, beryllium-, or rare-earth minerals.
Field identification & locations
The coarse pink, gray, and black intergrowth suggests quartz, feldspar, and mica; confirm by examining fresh surfaces and individual grains. Pegmatites occur worldwide in granitic terrains.
