metamorphic
Phyllite
Phyllite
Hardness: 1-2 (Mohs); Color: Silvery-gray, greenish, or brownish; Luster: Satiny, silky, or pearly; Crystal structure: Microcrystalline (foliated phyllitic texture); Cleavage: Perfect slaty-to-phyllitic cleavage; Specific gravity: 2.72-2.73
- Hardness
- 1-2 (Mohs)
- Color
- Silvery-gray, greenish, or brownish
- Luster
- Satiny, silky, or pearly
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Physical properties
Hardness: 1-2 (Mohs); Color: Silvery-gray, greenish, or brownish; Luster: Satiny, silky, or pearly; Crystal structure: Microcrystalline (foliated phyllitic texture); Cleavage: Perfect slaty-to-phyllitic cleavage; Specific gravity: 2.72-2.73
Formation & geological history
Formed through low-grade regional metamorphism of pelitic (clay-rich) sedimentary rocks like shale. It represents a metamorphic grade between slate and schist. It forms at temperatures of 200–350°C.
Uses & applications
Used primarily as decorative stone, roofing tiles (less commonly than slate), floor tiles, and as an aggregate for light construction. Limited industrial use due to its fissile nature.
Geological facts
The characteristic 'phyllitic luster' or satin-like sheen is caused by the alignment of microscopic grains of mica (sericite) and chlorite reflecting light. The name comes from the Greek 'phyllon,' meaning leaf.
Field identification & locations
Identify by its characteristic wavy foliation and satiny sheen that reflects light more brightly than slate but lacks the visible large mica flakes of schist. Found in mountainous or formerly tectonically active regions like the Appalachians or the Alps.
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