igneous
Quartz-bearing pegmatite, possibly with mica
Granitic pegmatite; chiefly quartz (SiO₂) and feldspar, with probable mica and dark accessory minerals
AI-generated identification · may be incorrectCoarse-grained, white to gray, glassy-to-vitreous quartz with blocky feldspar and dark mica/inclusions; quartz hardness 7, feldspar 6–6.5, mica 2–3, with poor cleavage in quartz and prominent cleavage in feldspar/mica. Specific gravity is roughly 2.6–2.7.
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Physical properties
Coarse-grained, white to gray, glassy-to-vitreous quartz with blocky feldspar and dark mica/inclusions; quartz hardness 7, feldspar 6–6.5, mica 2–3, with poor cleavage in quartz and prominent cleavage in feldspar/mica. Specific gravity is roughly 2.6–2.7.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in late-stage veins, allowing unusually large crystals to grow, generally during Precambrian to Phanerozoic intrusive events. The exact locality and age cannot be determined from the image.
Uses & applications
Used as a source of feldspar, quartz, mica, and occasionally lithium or rare metals; attractive pieces are collected as cabinet specimens, but this example appears common and is unlikely to be jewelry grade.
Geological facts
Pegmatites can contain exceptionally large crystals and valuable minerals such as tourmaline, beryl, spodumene, and columbite. The specimen’s white mass is likely quartz–feldspar rather than a single mineral.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, the United States, Canada, Madagascar, and India. Look for very coarse interlocking crystals, glassy quartz, feldspar cleavage, and flaky mica; a close-up or hardness/streak tests would improve identification.
