![Schist (Mica Schist (formula variable based on mineral content, typically containing [K,Al,Fe,Mg,Si,O,H])) — metamorphic](https://media.rockidentification.com/12405431-094d-4261-b90a-9ccea52ba54d-compressed.jpg)
metamorphic
Schist
Mica Schist (formula variable based on mineral content, typically containing [K,Al,Fe,Mg,Si,O,H])
Hardness: 3.5–4.0; Color: Greys, browns, and dark greens with visible silvery mica flakes; Luster: Pearly to vitreous/sub-metallic; Crystal structure: Monoclinic; Cleavage: Perfect basal (foliation plates); Specific gravity: 2.7–2.8.
- Hardness
- 3
- Luster
- Pearly to vitreous/sub-metallic
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Physical properties
Hardness: 3.5–4.0; Color: Greys, browns, and dark greens with visible silvery mica flakes; Luster: Pearly to vitreous/sub-metallic; Crystal structure: Monoclinic; Cleavage: Perfect basal (foliation plates); Specific gravity: 2.7–2.8.
Formation & geological history
Formed through the regional metamorphism of shale, mudstone, or igneous rocks under medium-to-high pressure and temperature conditions. It typically represents a higher grade of metamorphism than phyllite but lower than gneiss.
Uses & applications
Primarily used as a decorative building stone for flagstone, walls, and landscaping. Higher-quality specimens sometimes used for jewelry if industrial garnets are present, but generally lacks industrial strength due to its tendency to flake.
Geological facts
The word 'schist' is derived from the Greek word 'schizein,' meaning 'to split,' which refers to the ease with which the rock can be divided into thin plates along its foliation planes. Ancient civilizations used it for carving and tablets.
Field identification & locations
Identify in the field by its 'schistosity'—a sparkly, layered appearance with large, visible mineral grains. Common in mountain ranges and plate boundaries globally, such as the Appalachians or the Alps. Collector's tip: Look for 'porphyroblasts' like garnets or staurolite embedded within the mica layers.
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