igneous
Pegmatite with mica and feldspar
Granitic pegmatite; chiefly quartz (SiO₂), feldspar, and mica, possibly with tourmaline or sulfides
AI-generated identification · may be incorrectCoarse-grained, light gray to pink and dark brown/black; vitreous quartz, pearly mica, and blocky feldspar. Hardness varies from 2–3 for mica to 6–7 for quartz/feldspar; irregular fracture with mica cleavage and typical specific gravity around 2.6–2.8.
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Physical properties
Coarse-grained, light gray to pink and dark brown/black; vitreous quartz, pearly mica, and blocky feldspar. Hardness varies from 2–3 for mica to 6–7 for quartz/feldspar; irregular fracture with mica cleavage and typical specific gravity around 2.6–2.8.
Formation & geological history
Formed when water-rich, silica-rich magma cooled slowly in veins near a granitic intrusion, allowing exceptionally large crystals to grow. Most pegmatites formed during Precambrian to Phanerozoic intrusive events.
Uses & applications
Used as a source of feldspar, quartz, mica, lithium, beryl, and tantalum; attractive specimens are collected, while gem-quality pockets may yield tourmaline, beryl, or spodumene.
Geological facts
The specimen’s extremely coarse interlocking crystals and shiny platy mica strongly indicate pegmatite rather than ordinary granite.
Field identification & locations
Identify it by centimeter-scale crystals, glassy quartz, pink/white feldspar, and easily splitting mica; common in granitic terrains worldwide, including Brazil, the United States, Madagascar, and Afghanistan. The image alone cannot confirm accessory minerals.
