metamorphic
Phyllite
Phyllite (Foliated metamorphic rock)
Hardness: 1-2 (on Mohs scale); Color: Silvery-gray, greenish, or blackish; Luster: Satiny or pearly sheen; Structure: Foliated, fine-grained; Cleavage: Excellent slaty cleavage; S.G.: 2.72-2.73
- Hardness
- 1-2 (on Mohs scale)
- Color
- Silvery-gray, greenish, or blackish
- Luster
- Satiny or pearly sheen
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Physical properties
Hardness: 1-2 (on Mohs scale); Color: Silvery-gray, greenish, or blackish; Luster: Satiny or pearly sheen; Structure: Foliated, fine-grained; Cleavage: Excellent slaty cleavage; S.G.: 2.72-2.73
Formation & geological history
Formed through regional metamorphism of shale, siltstone, or slate under low-to-intermediate pressure and temperature conditions. It represents a metamorphic grade between slate and schist.
Uses & applications
Used primarily as decorative stone in landscaping, flagstones for pathways, and occasionally as roofing material or in flooring due to its attractive sheen.
Geological facts
The characteristic sheen of phyllite is caused by the alignment of tiny mica crystals (sericite and chlorite) that are too small to see individually with the naked eye but reflect light together.
Field identification & locations
Identify in the field by its distinct satiny sheen and its tendency to split into thin sheets. It is shinier than slate but finer-grained than schist. Commonly found in folded mountain belts like the Appalachians.
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