scoriae

/S K AO1 R IY0 EY0/
noun
  1. 1

    The slag or dross that remains after the smelting of metal from an ore.

  2. 2

    Rough masses of rock formed by solidified lava, and which can be found around a volcano's crater.

Source: https://en.wiktionary.org/wiki/scoria, https://en.wiktionary.org/wiki/scoriae