Phyllite is a foliated metamorphic rock that formed when fine-grained sedimentary rock such as shale or mudstone was buried and mildly altered by the heat and directed pressure of regional metamorphism. It is composed mainly of flake-shaped mica minerals in strong parallel alignment, which allows the rock to be easily split into sheets or slabs. It is primarily composed of quartz, sericite mica, and chlorite.

Phyllite’s Physical Properties

1. Color: gray, black, tan, brown
2. Streak:white
3. Luster: Phyllitic (Silvery, Nonmetallic)
4. Cleavage/Fracture: Phyllitic cleavage (Slaty, One flat or crinkled plane)
5. Hardness: 1-2
6. Specific Gravity: 2.72-2.73
7. Texture: Foliated; Fine-grained