Phyllite
Mineral NamePhyllite
Chemical FormulaComplex, composed primarily of fine-grained micas (muscovite, chlorite) and quartz
Mohs HardnessVariable, 2-7 (depending on constituent minerals)
Streak ColorLight gray to white
CleavageExcellent phyllitic cleavage (schistosity), allowing it to split into thin, wavy sheets
FractureUneven to splintery, but primarily breaks along cleavage planes
Specific Gravity2.75
Colorssilvery-gray, gray, greenish-gray, blackish
TransparencyOpaque
Type LocalityWidespread in regions of regional metamorphism, e.g., Appalachian Mountains (USA), Scottish Highlands, Alps
Mineral GroupMetamorphic rock (composed of fine-grained micas, quartz, and other minerals)
UsesRoofing tiles, decorative stone, landscaping, aggregate
Associated MineralsQuartz, muscovite, chlorite, sericite, biotite, garnet, tourmaline
Raritycommon
Description
A silvery-gray, fine-grained metamorphic rock exhibiting a distinct wavy foliation and a satiny luster on its cleavage surfaces.
Geological Context
Phyllite forms under low-grade regional metamorphic conditions, intermediate between slate and schist, typically from the metamorphism of shale or pelitic sediments.
