metamorphic
Micaceous Schist
Mica Schist (primarily Muscovite or Biotite KAl2(AlSi3O10)(OH)2)
Hardness: 2-3 (on the Mohs scale for individual mica flakes); Color: Silvery-gray, brownish-gold, or greenish; Luster: Pearly to metallic (highly reflective); Crystal structure: Monoclinic (platy flakes); Cleavage: Perfect basal cleavage; Specific Gravity: 2.8 - 3.0.
- Hardness
- 2-3 (on the Mohs scale for individual mica flakes)
- Color
- Silvery-gray, brownish-gold, or greenish
- Luster
- Pearly to metallic (highly reflective)
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Physical properties
Hardness: 2-3 (on the Mohs scale for individual mica flakes); Color: Silvery-gray, brownish-gold, or greenish; Luster: Pearly to metallic (highly reflective); Crystal structure: Monoclinic (platy flakes); Cleavage: Perfect basal cleavage; Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (like shale or mudstone) at medium temperatures and pressures. This creates a foliation known as schistosity, where platy minerals like micas align in parallel layers.
Uses & applications
Used historically as a source of mica for electrical insulation and heat-resistant windows (muscovite). Today, crushed schist is used in construction as fill or road aggregate. Some specimens are used as decorative stone in gardens or masonry.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'to split,' referring to the ease with which it can be split along the layers of mica. It is the bridge between phyllite and gneiss in the metamorphic series.
Field identification & locations
Identify in the field by its distinct 'glittery' appearance when held up to the light; it often looks like it is covered in silver or gold flakes. It is commonly found in mountain belts such as the Appalachians or the Alps. You can often peel off tiny translucent flakes with a fingernail.
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