igneous
Quartz-rich pegmatite fragment
Pegmatite composed chiefly of quartz (SiO₂), with probable feldspar and mica inclusions
AI-generated identification · may be incorrectCoarse, irregular granular texture; translucent gray-white quartz, dark gray/brown areas, and vitreous to pearly luster. Quartz hardness is 7 Mohs, with no cleavage; feldspar is about 6–6.5 and has two cleavages. Exact identification is limited by the small, weathered specimen.
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Physical properties
Coarse, irregular granular texture; translucent gray-white quartz, dark gray/brown areas, and vitreous to pearly luster. Quartz hardness is 7 Mohs, with no cleavage; feldspar is about 6–6.5 and has two cleavages. Exact identification is limited by the small, weathered specimen.
Formation & geological history
An intrusive igneous rock formed when volatile-rich magma cooled slowly, allowing unusually large crystals to grow, commonly during the late stages of a granitic intrusion. Pegmatites are generally Precambrian to Cenozoic in age depending on the host intrusion.
Uses & applications
Used as a source of quartz, feldspar, mica, and rare elements; attractive pieces are collected, while larger clean crystals may be cut or used decoratively.
Geological facts
Pegmatites commonly host spectacular crystals and rare minerals such as tourmaline, beryl, spodumene, and columbite-tantalite.
Field identification & locations
Look for very coarse interlocking crystals, glassy quartz, blocky feldspar cleavage, and flaky mica; common in granite and metamorphic terrains worldwide. A streak test and hardness test can help distinguish quartz from feldspar.
