igneous
Quartz-bearing pegmatite fragment
Granitic pegmatite; chiefly quartz (SiO₂), with probable feldspar and dark mica/amphibole
AI-generated identification · may be incorrectHardness about 6–7 (quartz), white to gray, vitreous quartz luster, coarse interlocking crystals, and irregular fracture; feldspar may show cleavage. The dark grains are likely biotite mica or amphibole, but the small specimen limits certainty.
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Physical properties
Hardness about 6–7 (quartz), white to gray, vitreous quartz luster, coarse interlocking crystals, and irregular fracture; feldspar may show cleavage. The dark grains are likely biotite mica or amphibole, but the small specimen limits certainty.
Formation & geological history
A pegmatite crystallizes from the final, water-rich melt of a granitic magma, producing exceptionally coarse crystals in veins and pockets. Pegmatites are generally Phanerozoic to Precambrian in age, depending on locality.
Uses & applications
Used as a source of quartz, feldspar, mica, lithium, and other rare minerals; attractive pieces are collected, though this fragment has modest specimen value.
Geological facts
The image shows a pale, massive matrix with translucent-looking gray areas and dark inclusions, consistent with weathered granitic pegmatite rather than a single mineral.
Field identification & locations
Look for very coarse crystals, glassy quartz, blocky feldspar, and platy mica. Common in granite terrains worldwide, including Brazil, the United States, Madagascar, and Scandinavia; a streak, hardness, and acid test can refine identification.
