igneous
Pegmatitic mica-bearing rock, likely muscovite granite pegmatite
Granitic pegmatite composed mainly of quartz, feldspar, and muscovite; dark grains may be biotite or tourmaline
AI-generated identification · may be incorrectCoarse-grained, uneven texture with prominent brown-gold mica books showing excellent basal cleavage and pearly vitreous luster. Quartz is typically Mohs 7, feldspar 6–6.5, and muscovite 2–2.5; overall color is gray, tan, brown, and black.
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Physical properties
Coarse-grained, uneven texture with prominent brown-gold mica books showing excellent basal cleavage and pearly vitreous luster. Quartz is typically Mohs 7, feldspar 6–6.5, and muscovite 2–2.5; overall color is gray, tan, brown, and black.
Formation & geological history
Formed from the final, water-rich fluids of slowly cooling granitic magma, allowing unusually large crystals to grow, generally during Precambrian–Mesozoic intrusive events. The specimen appears naturally weathered and unpolished.
Uses & applications
Used primarily as a collector specimen; pegmatite minerals can provide feldspar, quartz, mica, lithium, beryl, and rare gemstones. Attractive varieties are used decoratively, but this piece is not gem quality.
Geological facts
Large mica crystals are characteristic of pegmatites and split into thin elastic sheets. Brown mica is commonly phlogopite or weathered biotite, while golden transparent plates may be muscovite.
Field identification & locations
Identify it by very coarse interlocking crystals, flaky sheets with perfect cleavage, and glassy quartz alongside blocky feldspar. Common worldwide near granitic intrusions, including Brazil, Madagascar, the United States, and Scandinavia.
