igneous
Pegmatite (with Muscovite Mica and Quartz)
Granitic Pegmatite (chiefly KAlSi3O8, SiO2, and KAl2(AlSi3O10)(OH)2)
Hardness: 6-7 (overall matrix), Color: White, silvery-gray, and tan. Luster: Pearly to vitreous. Crystal structure: Phaneritic (large visible crystals). Cleavage: Perfect basal cleavage in the mica flakes.
- Hardness
- 6-7 (overall matrix), Color: White, silvery-gray, and tan
- Color
- White, silvery-gray, and tan
- Luster
- Pearly to vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 (overall matrix), Color: White, silvery-gray, and tan. Luster: Pearly to vitreous. Crystal structure: Phaneritic (large visible crystals). Cleavage: Perfect basal cleavage in the mica flakes.
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of exceptionally large crystals. Typically found in batholiths or dikes.
Uses & applications
Source of industrial minerals like mica (insulation), quartz (glass/electronics), and feldspar (ceramics). Also collected for mineral specimens.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth. The silvery, flaky parts are Muscovite, which was historically used as 'Muscovy-glass' for windows in Russia.
Field identification & locations
Identify in the field by the exceptionally large, interlocking crystals and the presence of 'books' of reflective, flaky mica that can be peeled into thin layers.
