metamorphic
Graphite Schist
C (Carbonaceous Schist)
Hardness: 1-2 (very soft); Color: Steel grey to black; Luster: Metallic to sub-metallic; Crystal Structure: Hexagonal (as graphite flakes within foliation); Cleavage: Perfect basal; Specific Gravity: 2.1-2.3
- Hardness
- 1-2 (very soft)
- Color
- Steel grey to black
- Luster
- Metallic to sub-metallic
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Physical properties
Hardness: 1-2 (very soft); Color: Steel grey to black; Luster: Metallic to sub-metallic; Crystal Structure: Hexagonal (as graphite flakes within foliation); Cleavage: Perfect basal; Specific Gravity: 2.1-2.3
Formation & geological history
Formed through regional metamorphism of carbon-rich sedimentary rocks (shales or mudstones). High pressure and temperature reorganize organic matter into graphite flakes aligned along planes of foliation. Typical geological ages range from Precambrian to Paleozoic.
Uses & applications
Industrial source of graphite for lubricants, 'lead' in pencils, and high-temperature crucibles. Some specimens are collected for educational or mineralogical purposes.
Geological facts
This rock can leave a dark grey streak on paper or skin just like a pencil. It is often greasy or soapy to the touch due to the lubricating properties of the graphite crystals.
Field identification & locations
Identified by its distinctive foliated (layered) texture, silver-grey metallic sheen, and its ability to be scratched by a fingernail. Commonly found in metamorphic belts like the Appalachians or the Alps.
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