metamorphic
Phyllite
Phyllite (Intermediate grade metamorphic rock)
Hardness: 1-2 (Mohs scale), Color: silvery-gray to greenish-gray, Luster: silky or pearly sheen, Crystal structure: foliated (microscopic mica crystals), Cleavage: excellent slaty cleavage.
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Physical properties
Hardness: 1-2 (Mohs scale), Color: silvery-gray to greenish-gray, Luster: silky or pearly sheen, Crystal structure: foliated (microscopic mica crystals), Cleavage: excellent slaty cleavage.
Formation & geological history
Formed through the regional metamorphism of pelitic (clay-rich) sedimentary rocks like shale. It represents a metamorphic grade between slate and schist.
Uses & applications
Mainly used as decorative stone, construction aggregate, or floor tiles. It is frequently collected by students and geologists to demonstrate metamorphic progression.
Geological facts
The characteristic sheen of phyllite is caused by the alignment of tiny flakes of muscovite or chlorite micas, which are just large enough to reflect light but too small to be seen individually by the naked eye.
Field identification & locations
Identified by its distinctive 'phyllitic sheen' and wavy foliation. It is commonly found in mountain belts (orogenic zones) and regions with old continental crust like the Appalachian Mountains.
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