The Collaborative International Dictionary
Slaggy \Slag"gy\, a. Of or pertaining to slag; resembling slag; as, slaggy cobalt.
Wiktionary
a. 1 (context of a material English) Resembling or containing slag. 2 (context UK Australia New Zealand pejorative of a person English) Resembling a slag, especially in behaviour.
Usage examples of "slaggy".
I was, closing in on that eyrie, filled with the treasure of a thousand years of tribute and the sweat of miners in a dozen slaggy towns among the Rivals who laboured in the shafts for the gold.
He was in his sixties, a slaggy choleric man with sparse hair covering his skull, as heavy-jowled as he was heavy-buttocked, but still a swift-moving man when action was required of him.
JPL about Nile, a dark and poisonous world where rain never reached the surface, a surface of slaggy black rocks hot enough to cook meat.