1. A fine-grained metamorphic rock formed from shale or mudstone, characterized by a silky sheen and the ability to split into thin sheets.
Usage: geology; technical

Examples

• The mountainside was composed largely of phyllite, which had been metamorphosed over millions of years.
• Phyllite is intermediate in grade between slate and schist.
• The miners extracted phyllite from the quarry for use as roofing material.
• Geologists identified phyllite layers in the rock formation during their field survey.
• The phyllite's characteristic sheen made it easy to distinguish from other metamorphic rocks.