metamorphic
Mica Schist with Garnet inclusions
Mica Schist (primarily Muscovite and Biotite - KAl2(AlSi3O10)(OH)2)
Hardness: 3.5 - 4 for sheet silicates, 6.5 - 7.5 for garnets; Color: Silvery-gray, reddish-brown, often glittering; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity); Cleavage: Perfect basal on mica flakes.
- Hardness
- 3
- Color
- Silvery-gray, reddish-brown, often glittering
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5 - 4 for sheet silicates, 6.5 - 7.5 for garnets; Color: Silvery-gray, reddish-brown, often glittering; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity); Cleavage: Perfect basal on mica flakes.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (shales or mudstones) under medium to high-grade temperature and pressure conditions during mountain-building events.
Uses & applications
Used as a decorative stone in architecture, as a component of some construction aggregates, and occasionally as a source for industrial mica in electronics or lubricants.
Geological facts
The glittering appearance is caused by the alignment of mica crystals that reflect light. It represents a higher metamorphic grade than phyllite but a lower grade than gneiss.
Field identification & locations
Identified by its obvious layering (foliation) and 'sparkly' or scaly appearance due to large mica flakes. Commonly found in ancient mountain belts like the Appalachians or the Alps. Collector tip: look for dark red 12-sided garnet crystals protruding from the mica layers.
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