sco·ri·a 
(skôrē-ə)
(skôrē-ə)n. pl. sco·ri·ae (skôrē-ē′)
1. Geology Porous cinderlike fragments of dark lava. Also called cinders, slag.
2. Metallurgy The refuse of a smelted metal or ore; slag. Also called cinder.
[Middle English, dross, from Latin scōria, from Greek skōriā, from skōr, excrement, dung; see sker-3 in the Appendix of Indo-European roots.]
sco′ri·aceous (-āshəs) adj.