metamorphic
Mica Schist
Mica Schist (Predominantly Muscovite/Biotite)
Hardness: 3.5-4; Color: Silvery-gray, brownish-gold, or tannish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistose texture); Cleavage: Perfect basal cleavage in mica flakes; Specific Gravity: 2.7-2.8
- Hardness
- 3
- Color
- Silvery-gray, brownish-gold, or tannish
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray, brownish-gold, or tannish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistose texture); Cleavage: Perfect basal cleavage in mica flakes; Specific Gravity: 2.7-2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under medium-grade temperature and pressure conditions. This specific piece is a water-worn river cobble, indicated by its rounded, smooth shape.
Uses & applications
Used occasionally as a decorative stone in landscaping, flagstone for walkways, or historically as a source of mica for industrial insulation.
Geological facts
The word schist comes from the Greek word 'schistos,' meaning 'split,' referring to the way the rock can be easily flaked into thin layers along its foliation planes. The sparkle is caused by the alignment of plate-like mica minerals.
Field identification & locations
Identify in the field by the distinct 'sparkle' or 'glitter' when rotated in sunlight. Look for a layered (foliated) appearance where individual flakes can sometimes be picked off with a fingernail. Common in mountain belts like the Appalachians or Himalayas.
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