The like stuff is in (w): hot metal; full of scoriae, which should and could have been smelted out, but which will not.
puhekieltä Rough masses of rock formed by solidified lava, and which can be found around a volcano's crater. (defdate)
2004, (w), The Earth, Folio Society 2011, p. 10:
An excellent guidebook by Drs Kilburn and McGuire of University College London reveals that these unpromising pieces of debris are scoria and lithic fragments of the March 1944 eruption.