igneous
Quartz-rich pegmatite
Granitic pegmatite, chiefly quartz (SiO₂), feldspar, and mica
AI-generated identification · may be incorrectCoarse, interlocking white to translucent quartz and pale feldspar with dark mica or accessory minerals; vitreous to pearly luster, irregular fracture, and hardness about 6–7 (quartz) or 6 (feldspar).
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Physical properties
Coarse, interlocking white to translucent quartz and pale feldspar with dark mica or accessory minerals; vitreous to pearly luster, irregular fracture, and hardness about 6–7 (quartz) or 6 (feldspar).
Formation & geological history
Formed when water-rich, silica-rich magma crystallized slowly in veins or pockets late in a granitic intrusion, producing unusually large crystals; commonly Precambrian to Phanerozoic in age.
Uses & applications
Used as a source of quartz and feldspar for glass, ceramics, and countertops; attractive specimens are collected, while gem-bearing pegmatites may yield tourmaline, beryl, or spodumene.
Geological facts
Pegmatites are among the best environments for exceptionally large crystals and rare-element minerals. The rusty brown areas likely represent iron-oxide staining from weathering.
Field identification & locations
Identify by its very coarse grain size, interlocking quartz-feldspar texture, and mica flakes; common in granitic mountain regions worldwide. A precise identification requires testing individual grains because the image alone cannot determine accessory minerals.
