scoria

English Thesaurus

1. the scum formed by oxidation at the surface of molten metals (noun.substance)

hypernym	:	scum,
definition	:	a film of impurities or vegetation that can form on the surface of a liquid (noun.artifact)

hyponym	:	basic slag,
definition	:	slag produced in making steel; low in silica but having large amounts of calcium phosphate; useful as fertilizer (noun.substance)