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The New International Encyclopædia/Pearlite

From Wikisource

Edition of 1905. See also Perlite on Wikipedia; and the disclaimer.

PEARLITE (so called on account of the pearly lustre). A glassy or once glassy rock which exhibits a ready separation by cracks into spherical or spheroidal forms. These so-called pearlitic cracks may arise from stresses set up during the cooling of the magma, or from differential expansion and contraction about spherulitic masses of feldspar.