igneous
Mica-rich pegmatite
Granitic pegmatite composed mainly of muscovite mica, quartz, and feldspar
AI-generated identification · may be incorrectCoarse-grained, interlocking crystals with abundant silvery to bronze, platy muscovite; quartz is typically glassy and feldspar whitish. Hardness is roughly 2–2.5 for muscovite, 6–7 for quartz, and 6 for feldspar; mica has perfect basal cleavage and a sparkling luster.
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Physical properties
Coarse-grained, interlocking crystals with abundant silvery to bronze, platy muscovite; quartz is typically glassy and feldspar whitish. Hardness is roughly 2–2.5 for muscovite, 6–7 for quartz, and 6 for feldspar; mica has perfect basal cleavage and a sparkling luster.
Formation & geological history
Forms when water-rich granitic magma cools slowly in dikes or pockets, allowing exceptionally large crystals to grow. Pegmatites are generally late Paleozoic to Mesozoic or younger, depending on their geological province.
Uses & applications
Used as a source of mica for electrical insulation, fillers, paints, and cosmetics; feldspar and quartz may be industrially useful. Attractive specimens are collected, though this piece appears common and cabinet-grade value is limited.
Geological facts
The large flaky crystals and coarse texture are diagnostic of pegmatite. Some pegmatites also host tourmaline, beryl, spodumene, and rare-element minerals.
Field identification & locations
Look for giant crystals, abundant cleavage flakes, and a granitic mixture rather than uniform schist. Common worldwide, especially in granitic terrains; likely localities include Brazil, the United States, Canada, Madagascar, and India.
