pearlite

noun
  1. 1

    A two-phased lamellar structure composed of alternating layers of alpha ferrite and cementite that occurs in some steels and cast irons, having a pearlescent appearance.

noun
  1. 1

    An amorphous volcanic glass formed by the hydration of obsidian.

  2. 2

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

Source: https://en.wiktionary.org/wiki/pearlite, https://en.wiktionary.org/wiki/perlite