metamorphic
Schist
Mica Schist (contains muscovite/biotite and quartz)
Hardness: 3.5-4 Mohs scale; Color: Silvery-gray, brownish-gold, or greenish; Luster: Pearly to metallic (silky appearance); Crystal structure: Monoclinic (within layers); Cleavage: Perfect basal cleavage in mica layers; Specific gravity: 2.7-2.8
- Hardness
- 3
- Color
- Silvery-gray, brownish-gold, or greenish
- Luster
- Pearly to metallic (silky appearance)
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Physical properties
Hardness: 3.5-4 Mohs scale; Color: Silvery-gray, brownish-gold, or greenish; Luster: Pearly to metallic (silky appearance); Crystal structure: Monoclinic (within layers); Cleavage: Perfect basal cleavage in mica layers; Specific gravity: 2.7-2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high pressure and temperature. It is characterized by 'schistosity,' the alignment of platy minerals. Geological ages range from Precambrian to Cenozoic depending on the mountain-building event.
Uses & applications
Used historically as a building stone, for decorative paving, and occasionally as a source for minerals like garnets. In modern times, it is used for high-quality flagstone and garden ornaments.
Geological facts
The word 'schist' comes from the Greek word 'schizein,' meaning 'to split,' referring to the way the rock easily flakes into thin layers. It is a medium-grade metamorphic rock, sitting between phyllite and gneiss in intensity.
Field identification & locations
Identify in the field by its distinct 'shimmer' or 'glitter' when rotated in sunlight and its tendency to flake into thin plates. Commonly found in metamorphic belts like the Appalachians or the Alps. Look for visible mica flakes and occasional trapped garnets.
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