Main Entry: per·lite

Pronunciation: \ˈpər-ˌlīt\

Function: noun

Etymology: French, from perle pearl

Date: 1833

: volcanic glass that has a concentric structure, appears as if composed of concretions, is usually grayish and sometimes spherulitic, and when heated expands to form a lightweight aggregate used especially in concrete and plaster and as a medium for potting plants

— per·lit·ic \ˌpər-ˈli-tik\ adjective