metamorphic
Schist
Mica Schist
Hardness: 3.5-4; Color: Silvery-gray, greenish, or golden-brown; Luster: Silky to pearly (due to mica); Crystal Structure: Foliated (schistose fabric); Cleavage: Perfect in one direction along mica plates; Specific Gravity: 2.7-2.9
- Hardness
- 3
- Color
- Silvery-gray, greenish, or golden-brown
- Luster
- Silky to pearly (due to mica)
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray, greenish, or golden-brown; Luster: Silky to pearly (due to mica); Crystal Structure: Foliated (schistose fabric); Cleavage: Perfect in one direction along mica plates; Specific Gravity: 2.7-2.9
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate pressure and temperature conditions. The alignment of mica flakes occurs as the rock is compressed, usually during mountain-building events (orogeny).
Uses & applications
Used historically as a building stone for walls and flooring; sometimes used as garden decoration. High-quality specimens with garnets or other minerals are sought by collectors.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'to split,' referring to the ease with which it can be divided into thin plates. It represents a higher grade of metamorphism than slate or phyllite.
Field identification & locations
Identify in the field by its distinct layered (foliated) appearance and the 'shimmer' it gives off when rotated in the sunlight due to the alignment of mica plates. It is commonly found in the cores of mountain ranges.
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