metamorphic
Muscovite Mica in Quartz
Potassium Aluminum Silicate Hydroxide (KAl2(AlSi3O10)(OH)2) and Silicon Dioxide (SiO2)
Hardness: 2-2.5 (Mica) / 7 (Quartz); Color: Silvery-gray, white, or colorless; Luster: Pearly to Vitreous; Crystal Structure: Monoclinic (sheets); Cleavage: Perfect basal cleavage producing thin, flexible flakes.
- Hardness
- 2-2
- Color
- Silvery-gray, white, or colorless
- Luster
- Pearly to Vitreous
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Physical properties
Hardness: 2-2.5 (Mica) / 7 (Quartz); Color: Silvery-gray, white, or colorless; Luster: Pearly to Vitreous; Crystal Structure: Monoclinic (sheets); Cleavage: Perfect basal cleavage producing thin, flexible flakes.
Formation & geological history
Commonly forms in regional metamorphic environments such as schists and gneisses, or in igneous pegmatites. This specimen likely originated from a pegmatite where slow cooling allowed for large mineral growth.
Uses & applications
Used as an electrical insulator, in high-pressure steam boiler windows, as a lubricant, and in cosmetics (glitter). Large, clear sheets are used in specialized furnace windows.
Geological facts
Until the 19th century, muscovite was mined in Russia for use as a glass substitute for windows, hence the name 'Muscovy-glass'. Its thin sheets can be split into layers thinner than a human hair.
Field identification & locations
Identify in the field by the 'book-like' layers of silvery flakes that reflect light brilliantly and can be easily peeled away with a fingernail or knife. Commonly found in mountainous regions with metamorphic outcrops.
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