igneous
Pegmatite with Mica
Granitic Pegmatite (containing Muscovite and Biotite)
Hardness: 6-7 (overall mass), 2.5 (mica); Color: Tan, white, and silver-black; Luster: Pearly to Vitreous; Crystal Structure: Very coarse-grained phaneritic; Cleavage: Perfect basal in mica flakes.
- Hardness
- 6-7 (overall mass), 2
- Color
- Tan, white, and silver-black
- Luster
- Pearly to Vitreous
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Physical properties
Hardness: 6-7 (overall mass), 2.5 (mica); Color: Tan, white, and silver-black; Luster: Pearly to Vitreous; Crystal Structure: Very coarse-grained phaneritic; Cleavage: Perfect basal in mica flakes.
Formation & geological history
Formed during the final stage of a magma's crystallization. Highly fluid, water-rich melts allow for extremely large crystal growth. Typical of continental crust environments.
Uses & applications
Major source of rare minerals (lithium, tantalum), mica for electrical insulation and cosmetics, and used in construction as crushed stone.
Geological facts
Pegmatites are known for having the largest crystals ever recorded in nature. The shiny flakes seen in the specimen were historically used as window glass (Muscovy glass) in Russia.
Field identification & locations
Look for exceptionally large mineral grains (over 1cm) and shiny, flaky plates of mica. Often found in mountainous or shield regions like the Appalachians or Black Hills.
