igneous
Quartz–feldspar pegmatite with garnet
Granitic pegmatite; chiefly quartz (SiO₂), feldspar, mica, and reddish-brown almandine garnet
AI-generated identification · may be incorrectCoarse interlocking crystals; white to translucent quartz/feldspar, brown mica, and red-brown garnet with vitreous to pearly luster. Quartz hardness is 7, feldspar 6–6.5, mica 2–3; feldspar shows cleavage, while quartz lacks cleavage.
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Physical properties
Coarse interlocking crystals; white to translucent quartz/feldspar, brown mica, and red-brown garnet with vitreous to pearly luster. Quartz hardness is 7, feldspar 6–6.5, mica 2–3; feldspar shows cleavage, while quartz lacks cleavage.
Formation & geological history
A pegmatite crystallizes from the final, water-rich melt of a granitic intrusion, producing exceptionally large crystals, generally during Precambrian to younger continental magmatism. The specimen appears weathered and naturally rounded.
Uses & applications
Used mainly as a collector specimen; pegmatites can host feldspar, mica, quartz, lithium minerals, and gem-quality garnet or tourmaline. Crushed pegmatite may serve as aggregate or ceramic/glass raw material.
Geological facts
The reddish-brown grains are likely garnet, while clear glassy areas are quartz; white opaque grains are probably feldspar. Exact identification requires a hand lens, hardness tests, and possibly thin-section or chemical analysis.
Field identification & locations
Common in granitic mountain regions and pegmatite districts worldwide, including Brazil, Madagascar, the United States, and Scandinavia. Look for very coarse crystals, feldspar cleavage, quartz’s conchoidal fracture, and garnet’s lack of cleavage.
