metamorphic
Muscovite Schist
Muscovite Mica Schist (KAl2(AlSi3O10)(OH)2)
Hardness: 2.0-2.5 on Mohs scale (for individual mica flakes); Color: Silvery-gray, brownish, or golden-bronze; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic; Cleavage: Perfect basal cleavage, easily flaking into thin sheets.
- Hardness
- 2
- Color
- Silvery-gray, brownish, or golden-bronze
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 2.0-2.5 on Mohs scale (for individual mica flakes); Color: Silvery-gray, brownish, or golden-bronze; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic; Cleavage: Perfect basal cleavage, easily flaking into thin sheets.
Formation & geological history
Formed through the regional metamorphism of shale or clay-rich sedimentary rocks under medium-grade pressure and temperature conditions (typically during mountain-building events). It represents a step up in metamorphism from phyllite.
Uses & applications
Used as a source of scrap mica for electrical insulation, ground into fillers for paints and plastics, and occasionally used in landscaping or as low-cost decorative garden stones.
Geological facts
The name 'Muscovite' comes from 'Muscovy-glass,' as the mineral was once used as a window substitute in medieval Russia. The shiny flakes are often mistaken for gold or silver by amateur prospectors, earning them the nickname 'Fool's Silver.'
Field identification & locations
Identify in the field by its distinct foliation (layering) and the way it reflects light intensely due to the mica content. It feels slightly greasy or soapy to the touch and can often be scratched with a fingernail or a copper penny. Commonly found in Appalachian Mountains and the Alps.
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