igneous
Pegmatite with Quartz and Muscovite Mica
Granitic Pegmatite (KAl2(AlSi3O10)(OH)2 + SiO2)
Hardness: 6-7 (quartz) and 2-2.5 (mica); Color: White, silvery-grey, light brown; Luster: Vitreous to pearly; Crystal structure: Monoclinic (mica) and Trigonal (quartz); Cleavage: Perfect basal (mica) and none (quartz).
- Hardness
- 6-7 (quartz) and 2-2
- Color
- White, silvery-grey, light brown
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 (quartz) and 2-2.5 (mica); Color: White, silvery-grey, light brown; Luster: Vitreous to pearly; Crystal structure: Monoclinic (mica) and Trigonal (quartz); Cleavage: Perfect basal (mica) and none (quartz).
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. These are typically found in plutonic environments.
Uses & applications
Source of industrial mica for electrical insulation and heat resistance; quartz is used in glass and electronics. Also popular for geological specimen collecting.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth. Mica was historically used for stove windows and 'isinglass' before modern heat-resistant glass was invented.
Field identification & locations
Identify by large, visible interlocking crystals and the 'books' of flaky, shiny mica. Found globally in continental shield areas and mountain ranges like the Appalachians or Rockies.
