igneous
Granite Pegmatite with Muscovite Mica
Granite Pegmatite (Silicon Dioxide and complex silicates)
Hardness: 6-7 (Quartz/Feldspar) and 2-2.5 (Mica); Color: White, cream, and silver-grey; Luster: Vitreous to Pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Perfect basal in mica flakes.
- Hardness
- 6-7 (Quartz/Feldspar) and 2-2
- Color
- White, cream, and silver-grey
- Luster
- Vitreous to Pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 (Quartz/Feldspar) and 2-2.5 (Mica); Color: White, cream, and silver-grey; Luster: Vitreous to Pearly; Crystal structure: Coarse-grained phaneritic; Cleavage: Perfect basal in mica flakes.
Formation & geological history
Formed during the final stages of a magma's crystallization. Highly fluid, water-rich melts allow for the growth of large crystals in intrusive environments. Commonly found in batholiths and orogenic belts.
Uses & applications
Source of industrial minerals like mica (insulation, cosmetics), quartz (electronics), and feldspar (ceramics). Also collected as geological specimens.
Geological facts
Pegmatites often contain rare earth elements and some of the largest individual crystals ever recorded. The sparkly silver flakes are Muscovite, often called 'Isinglass' and were historically used as heat-resistant window material.
Field identification & locations
Identify by exceptionally large crystal size compared to surrounding rock and the presence of 'books' or flakes of shiny mica that can be peeled with a fingernail. Found in mountainous or crystalline basement regions.
