metamorphic
Phyllite
Phyllite
Hardness: 1-2 (Mohs scale); Color: Silvery-gray, greenish, or golden-brown due to mica; Luster: Silky, pearly, or sub-metallic phyllitic sheen; Crystal Structure: Foliated with very fine-grained mica crystals; Cleavage: Perfect slaty-like cleavage; Specific Gravity: 2.72-2.73.
- Hardness
- 1-2 (Mohs scale)
- Color
- Silvery-gray, greenish, or golden-brown due to mica
- Luster
- Silky, pearly, or sub-metallic phyllitic sheen
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Physical properties
Hardness: 1-2 (Mohs scale); Color: Silvery-gray, greenish, or golden-brown due to mica; Luster: Silky, pearly, or sub-metallic phyllitic sheen; Crystal Structure: Foliated with very fine-grained mica crystals; Cleavage: Perfect slaty-like cleavage; Specific Gravity: 2.72-2.73.
Formation & geological history
Formed by the regional metamorphism of pelitic sedimentary rocks (like shale or siltstone). It represents an intermediate grade between slate and schist, forming at temperatures of 300 to 450 degrees Celsius and moderate pressure.
Uses & applications
Occasionally used as decorative stone, roofing material, for floor tiling, or as crushed stone in construction where high durability isn't required. Its primary value is geological study.
Geological facts
The word 'phyllite' comes from the Greek 'phyllon', meaning 'leaf', referring to its thin, leaf-like layers. It is distinguished from slate by its lustrous sheen caused by the alignment of tiny mica crystals (sericite or chlorite).
Field identification & locations
Identify in the field by its characteristic silky sheen and wavy foliation surfaces. It is often found in mountain belts formed by plate tectonics, such as the Appalachian Mountains or the Alps. Unlike schist, its mica grains are too small to be seen individually by the naked eye.
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