igneous
Quartz-bearing pegmatitic rock, likely granite/pegmatite
Feldspar–quartz pegmatite; chiefly K-feldspar, plagioclase, quartz, and possible mica
AI-generated identification · may be incorrectCoarse-grained, irregular pale cream feldspar and gray translucent quartz with vitreous to pearly luster; hardness about 6–7 Mohs, nonfoliated, with feldspar cleavage and quartz fracture. The dark portion may be biotite, amphibole, or an attached mafic inclusion.
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Physical properties
Coarse-grained, irregular pale cream feldspar and gray translucent quartz with vitreous to pearly luster; hardness about 6–7 Mohs, nonfoliated, with feldspar cleavage and quartz fracture. The dark portion may be biotite, amphibole, or an attached mafic inclusion.
Formation & geological history
A late-stage igneous melt crystallized slowly in a granitic intrusion or vein, producing unusually large crystals; commonly Precambrian to Phanerozoic in age. The specimen appears naturally fractured rather than polished.
Uses & applications
Pegmatite is quarried for feldspar, quartz, mica, lithium, and other rare-element minerals; attractive pieces are used as mineral specimens and occasionally in decorative stone. This example has modest display value unless rare minerals are present.
Geological facts
Pegmatites can host tourmaline, beryl, garnet, spodumene, and economic lithium minerals. The cream material is probably feldspar, while the gray glassy material is likely quartz.
Field identification & locations
Look for very coarse interlocking crystals, feldspar cleavage, and quartz that scratches glass but lacks cleavage; a streak test and hardness test can help. Common worldwide in regions with granitic batholiths, including Maine, California, Brazil, Madagascar, and Scandinavia.
