01 n. A glassy volcanic rock of a grayish color and pearly luster, often having a spherulitic concretionary structure due to the curved cracks pr…
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1.
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.(Min.) See: Perlitic