igneous
Granitic Pegmatite (Muscovite and Quartz)
Pegmatite (KAl2(AlSi3O10)(OH)2 / SiO2)
Hardness: 2.5 (Muscovite) to 7 (Quartz); Color: Silvery-gray, white, and translucent beige/brown; Luster: Pearly to Vitreous; Crystal structure: Monoclinic (Mica) and Hexagonal (Quartz); Cleavage: Perfect basal cleavage in the mica portions.
- Hardness
- 2
- Color
- Silvery-gray, white, and translucent beige/brown
- Luster
- Pearly to Vitreous
Identified More igneous →
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Physical properties
Hardness: 2.5 (Muscovite) to 7 (Quartz); Color: Silvery-gray, white, and translucent beige/brown; Luster: Pearly to Vitreous; Crystal structure: Monoclinic (Mica) and Hexagonal (Quartz); Cleavage: Perfect basal cleavage in the mica portions.
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 batholiths or metamorphic belts.
Uses & applications
Used as a source of industrial minerals like mica for insulation and electronics, or quartz for glassmaking. Large specimens are valued for geological study and mineral collecting.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth, sometimes reaching over 10 meters in length. This specimen shows 'books' of muscovite mica embedded within a quartz/feldspar matrix.
Field identification & locations
Identify in the field by the unusually large crystal size compared to surrounding granitic rocks. Look for the characteristic 'flaking' of silvery mica layers. Common in mountain ranges with exposed Precambrian shields.
