Granitic Pegmatite (Muscovite and Quartz)

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.

Identified on: 4/24/2026

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