metamorphic
Mica Schist
Mica Schist (Main mineral constituents: Muscovite/Biotite, Quartz, Feldspar)
Hardness: 2-3 (mica) to 6-7 (overall rock); Color: Silvery-gray to brownish; Luster: Pearly to metallic (glittery); Crystal structure: Platy/Foliated; Cleavage: Excellent basal cleavage in mica flakes; Specific gravity: 2.7-2.9
- Hardness
- 2-3 (mica) to 6-7 (overall rock)
- Color
- Silvery-gray to brownish
- Luster
- Pearly to metallic (glittery)
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Physical properties
Hardness: 2-3 (mica) to 6-7 (overall rock); Color: Silvery-gray to brownish; Luster: Pearly to metallic (glittery); Crystal structure: Platy/Foliated; Cleavage: Excellent basal cleavage in mica flakes; Specific gravity: 2.7-2.9
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high pressure and temperature. This process aligns mineral grains into parallel layers, creating schistosity. Most date from the Precambrian to Paleozoic eras.
Uses & applications
Used primarily as decorative stone, flagstone for walkways, and sometimes as a minor source of mica for electrical insulation or as a fill material in construction.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'split,' referring to the ease with which it can be split along the layers of mica. It is the most common metamorphic rock found in the Earth's crust.
Field identification & locations
Identify by its sparkly, 'glitter' appearance and its ability to peel or flake off in thin layers. It is ubiquitous in mountainous regions such as the Appalachians, Alps, and Himalayas. Collectors look for large garnet or staurolite crystals embedded within it.
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