igneous
Granitic Pegmatite
Pegmatite (composed primarily of Quartz, Feldspar, and Muscovite mica)
Hardness: 6-7 (Mohs scale); Color: White, cream, tan with silvery-grey flakes; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (very large crystals); Cleavage: Perfect in one direction for the mica components; Specific gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs scale)
- Color
- White, cream, tan with silvery-grey flakes
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: White, cream, tan with silvery-grey flakes; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (very large crystals); Cleavage: Perfect in one direction for the mica components; Specific gravity: 2.6-2.7
Formation & geological history
Formed during the final stages of a magma chamber's crystallization when high water content allow large crystals to grow rapidly. These are typically associated with batholiths and found in ancient continental crust.
Uses & applications
Used as a source of rare minerals and gemstones; also used in ceramics, glass making, and decorative architectural stone.
Geological facts
Pegmatites are famous for containing some of the largest crystals ever recorded, sometimes exceeding 10 meters in length. The silvery flakes seen in the specimen are likely Muscovite mica.
Field identification & locations
Identify in the field by exceptionally large, interlocking crystals of quartz and feldspar. Found in mountainous or shield regions like the Black Hills (USA) or Minas Gerais (Brazil). Collectors look for well-formed mica plates or embedded gems.
