metamorphic
Schist (Graphite or Mica rich)
Crystalline Schist (often containing Muscovite, Biotite, or Graphite)
Hardness: 1-3 (if graphite rich) up to 6-7 (if containing garnets/quartz); Color: Silver, gray, to black with a metallic or pearly sheen; Luster: Sub-metallic to vitreous; Crystal structure: Foliated/Schistose; Cleavage: Perfect basal cleavage in individual flakes; Specific gravity: 2.7-2.8.
- Color
- Silver, gray, to black with a metallic or pearly sheen
- Luster
- Sub-metallic to vitreous
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Physical properties
Hardness: 1-3 (if graphite rich) up to 6-7 (if containing garnets/quartz); Color: Silver, gray, to black with a metallic or pearly sheen; Luster: Sub-metallic to vitreous; Crystal structure: Foliated/Schistose; Cleavage: Perfect basal cleavage in individual flakes; Specific gravity: 2.7-2.8.
Formation & geological history
Formed through regional metamorphism of shale or mudstone under intermediate to high pressure and temperature. Its age varies by tectonic location, often found in ancient Orogenic belts (mountain building event zones).
Uses & applications
Used historically as a decorative stone, in construction as flagstone, and occasionally as a source of graphite if the concentration is high enough. Primarily of architectural and geological interest.
Geological facts
The characteristic 'shimmer' of schist is due to the alignment of flat mineral grains (like mica) during intense tectonic pressure. It is the intermediate step between phyllite and gneiss in the metamorphic sequence.
Field identification & locations
Identify in the field by its distinct foliation (layering) and the tendency to flake off in thin sheets. Commonly found in the Appalachian Mountains (USA), Scotland, and the Alps. Collectors look for 'garnet-schist' containing red garnets.
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