metamorphic
Phyllite
Phyllite (regional metamorphic rock)
Hardness: 1-2 (Mohs); Color: Silvery-gray, greenish, or black; Luster: Silky, pearly, or metallic sheen; Crystal structure: Microcrystalline mica (muscovite/chlorite); Cleavage: Perfect slaty/phyllitic cleavage; Specific Gravity: 2.7-2.8
- Hardness
- 1-2 (Mohs)
- Color
- Silvery-gray, greenish, or black
- Luster
- Silky, pearly, or metallic sheen
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Physical properties
Hardness: 1-2 (Mohs); Color: Silvery-gray, greenish, or black; Luster: Silky, pearly, or metallic sheen; Crystal structure: Microcrystalline mica (muscovite/chlorite); Cleavage: Perfect slaty/phyllitic cleavage; Specific Gravity: 2.7-2.8
Formation & geological history
Formed by regional metamorphism of pelitic (clay-rich) sedimentary rocks like shale. It represents an intermediate grade between slate and schist, forming at higher temperatures and pressures than slate.
Uses & applications
Primarily used as decorative stone in landscaping, roofing tiles, and occasionally as a source of industrial mica or in construction aggregate.
Geological facts
Phyllite is distinguished from slate by its characteristic 'silky' sheen, caused by the alignment of microscopic mica grains that reflect light. It often exhibits 'crenulations' or tiny waves in its cleavage planes.
Field identification & locations
Identify by its satiny luster and the way it splits into thin, slightly wavy sheets. Common in orogenic belts (mountain-building regions) like the Appalachian Mountains or the Scottish Highlands.
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