scoria

Seen in a submission. "Scoria" (derived eventually from Greek "skōr," meaning "excrement") means "slag." Emphasis on first syllable.

Amusingly, MW11 defines "scoria" as "slag," and defines "slag" as "the dross or scoria of a metal." But the "scoria" definition has a little more detail, so it's not an entirely circular pair of definitions.