| n. | 1. | (Min.) A glassy volcanic rock of a grayish color and pearly luster, often having a spherulitic concretionary structure due to the curved cracks produced by contraction in cooling. See Illust. under Perlitic. |
| Noun | 1. | pearlite - a lamellar mixture of cementite and ferrite formed during the cooling of austenite; a micro-constituent of steel and cast iron |