metamorphic
Schist
Mica Schist (Group of medium-grade metamorphic rocks)
Hardness: 3.5-4 Mohs scale; Color: Silvery-grey to black with visible sparkle; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistose); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.8
- Hardness
- 3
- Color
- Silvery-grey to black with visible sparkle
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 Mohs scale; Color: Silvery-grey to black with visible sparkle; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistose); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high pressure and temperature (medium rank). It is characterized by the alignment of plate-like minerals such as mica, which grow large enough to be seen with the naked eye.
Uses & applications
Used primarily as decorative stone in landscaping, flagstones, and sometimes as a minor source of mica for industrial insulation or fillers. Occasionally used in jewelry if it contains garnets.
Geological facts
The term 'schist' is derived from the Greek word 'schizein,' meaning 'to split,' referring to the way the rock can be easily flaked along its mineral layers. It often contains 'porphyroblasts'—large crystals like garnet or staurolite—that grew within the matrix.
Field identification & locations
Identify in the field by its 'schistosity' (strong foliation) and the way it glitters in the sunlight due to mica content. Commonly found in the crystalline cores of mountain ranges such as the Appalachians, Alps, or Himalayas.
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