metamorphic
Mica Schist
Muscovite/Biotite Schist
Hardness: 3.5-4 Mohs (for the schist as a whole), Color: Silvery-grey to golden-bronze, Luster: Pearly to metallic (vitreous), Crystal Structure: Monoclinic (foliated/schistose), Cleavage: Perfect basal cleavage in mica minerals, Specific Gravity: 2.7-3.0
- Hardness
- 3
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Physical properties
Hardness: 3.5-4 Mohs (for the schist as a whole), Color: Silvery-grey to golden-bronze, Luster: Pearly to metallic (vitreous), Crystal Structure: Monoclinic (foliated/schistose), Cleavage: Perfect basal cleavage in mica minerals, Specific Gravity: 2.7-3.0
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This creates large mica crystals that align perpendicular to the direction of pressure, giving the rock its characteristic shine.
Uses & applications
Used historically as a building stone and for flagstones. Mica flakes are often extracted for use as insulators in electrical equipment, fillers in paint/plastic, and as a shimmering agent in cosmetics.
Geological facts
The word 'schist' comes from the Greek word 'schistos', meaning 'split', referring to the ease with which the rock can be split into thin plates. It represents a higher grade of metamorphism than slate or phyllite.
Field identification & locations
Identify in the field by its 'schistose' texture, where minerals are large enough to be seen with the naked eye and exhibit strong foliation and shimmering luster. Commonly found in mountain belts and Precambrian shield areas.
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