igneous
Quartz-rich granitic pegmatite fragment
Pegmatite, composed mainly of quartz (SiO₂), feldspar, and mica
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals with white-gray translucent quartz, pale feldspar, and sparkling dark mica; vitreous quartz luster, Mohs hardness about 6–7, poor or absent overall cleavage, and typical specific gravity around 2.6–2.7.
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Physical properties
Coarse, irregular interlocking crystals with white-gray translucent quartz, pale feldspar, and sparkling dark mica; vitreous quartz luster, Mohs hardness about 6–7, poor or absent overall cleavage, and typical specific gravity around 2.6–2.7.
Formation & geological history
A pegmatite crystallizes from the final, water-rich fluids of a cooling felsic magma, producing unusually large crystals; its exact geological age cannot be determined from the photograph. It commonly occurs in granite bodies and surrounding metamorphic rocks.
Uses & applications
Used as a source of quartz and feldspar for glass, ceramics, and aggregates; attractive pieces are collected, though this fragment has little jewelry value unless it contains gem minerals.
Geological facts
The apparent glitter is likely mica cleavage surfaces, while translucent areas are quartz. Pegmatites can host tourmaline, beryl, garnet, and rare lithium minerals.
Field identification & locations
Identify it by very coarse crystals, glassy quartz, blocky feldspar cleavage, and flaky mica; common localities include Maine, Connecticut, California, Brazil, and Madagascar. A hand lens and streak, hardness, and cleavage tests improve identification.
