igneous
Quartz with Mica (Pegmatite)
Quartz (SiO2) and Muscovite (KAl2(AlSi3O10)(OH)2)
Hardness: 7 (Quartz) and 2-2.5 (Mica); Color: White, tan, and silvery; Luster: Vitreous to pearly; Crystal structure: Hexagonal and monoclinic; No cleavage in Quartz, perfect basal cleavage in Mica; Specific gravity: 2.65-2.8.
- Hardness
- 7 (Quartz) and 2-2
- Color
- White, tan, and silvery
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 7 (Quartz) and 2-2.5 (Mica); Color: White, tan, and silvery; Luster: Vitreous to pearly; Crystal structure: Hexagonal and monoclinic; No cleavage in Quartz, perfect basal cleavage in Mica; Specific gravity: 2.65-2.8.
Formation & geological history
Formed from late-stage cooling of magma in a pegmatite vein where high water content allows for large crystal growth. These structures often date back hundreds of millions to billions of years.
Uses & applications
Quartz is used in electronics (oscillators), glassmaking, and construction. Muscovite mica is used in insulation and as a glimmering agent in cosmetics.
Geological facts
Pegmatites are known for being the primary source of multi-colored gemstones and rare earth minerals because they concentrate elements that don't fit into earlier-forming crystals.
Field identification & locations
Identify in the field by the distinct combination of crystalline white quartz and the 'flaky' or 'platty' texture of mica that can be peeled with a fingernail. Often found in mountainous granitic regions.
