Noun

(wikipedia perlite) (en noun)

(mineralogy) An amorphous volcanic glass formed by the hydration of obsidian.

The lightweight insulating material and aggregate resulting from expanding perlite glass by heat.

*{{quote-book, year=1928, author=Lawrence R. Bourne

, title=Well Tackled! , chapter=4 citation , passage=Technical terms like ferrite, perlite , graphite, and hardenite were bandied to and fro, and when Paget glibly brought out such a rare exotic as ferro-molybdenum, Benson forgot that he was a master ship-builder, […]}}