igneous
Pegmatite / Granite with Mica
Pegmatite (Igneous Rock composed of Quartz, Feldspar, and Muscovite Mica)
Hardness: 6-7 on Mohs scale (quartz/feldspar), Color: White, pink, tan, gray with silvery flash, Luster: Vitreous to pearly/metallic (mica flakes), Structure: Coarse-grained phaneritic or pegmatitic, Cleavage: Perfect basal cleavage on mica flakes
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Physical properties
Hardness: 6-7 on Mohs scale (quartz/feldspar), Color: White, pink, tan, gray with silvery flash, Luster: Vitreous to pearly/metallic (mica flakes), Structure: Coarse-grained phaneritic or pegmatitic, Cleavage: Perfect basal cleavage on mica flakes
Formation & geological history
Formed during the final stages of a magma chamber's crystallization, where water-rich magmatic fluids allow large crystals of quartz, feldspar, and mica to grow rapidly. Commonly found in plutonic environments and continental crustal collision zones.
Uses & applications
Mica is used in cosmetics, electrical insulators, paint, and drywall joint compound. Feldspar and quartz are widely used in ceramics, glassmaking, and construction aggregate. Large pegmatite bodies are often mined for rare elements like lithium, beryllium, and tantalum.
Geological facts
Muscovite mica in pegmatites can form giant sheets historically known as 'Isinglass', which was used for oven doors and church windows before glass manufacturing advanced.
Field identification & locations
Identified by the mixture of translucent quartz, pink/beige feldspar, and distinctly shiny, flakey mica sheets that peel or flash light. Collectors can easily find pegmatite in mountainous igneous terrains worldwide.
