metamorphic
Mica Schist
Medium-grade regional metamorphic rock (composition varies)
Hardness: 3.5-4 (Mohs); Color: Dark grey, charcoal, or silvery-black; Luster: Pearly to sub-metallic (schistose sheen); Crystal structure: Foliated with visible mica flakes; Cleavage: One perfect direction in mica minerals causing the rock to split into thin sheets.
- Hardness
- 3
- Color
- Dark grey, charcoal, or silvery-black
- Luster
- Pearly to sub-metallic (schistose sheen)
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Dark grey, charcoal, or silvery-black; Luster: Pearly to sub-metallic (schistose sheen); Crystal structure: Foliated with visible mica flakes; Cleavage: One perfect direction in mica minerals causing the rock to split into thin sheets.
Formation & geological history
Formed through regional metamorphism of shale or mudstone under intermediate temperature and pressure. It often dates back to various orogenic (mountain-building) events ranging from hundreds of millions to billions of years old.
Uses & applications
Used as a decorative garden stone, in landscaping, and historically for flagstones or roofing in mountain regions. It has little industrial value compared to marble or granite but is popular with amateur collectors for its sparkle.
Geological facts
The word 'schist' comes from the Greek 'schizein' meaning 'to split'. The sparkling appearance is due to the presence of phyllosilicates like biotite and muscovite aligning during intense geological pressure.
Field identification & locations
Identify in the field by its distinct foliation (layering), sparkling surface when held to light, and tendency to flake off in small plates. It is commonly found in mountain belts like the Appalachians, Alps, or Himalayas.
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