scoria

Meanings

1. 1
   noun

   rough, dark, porous lava formed when gas-rich molten rock cools

   Black scoria covered the slope around the volcanic crater.

2. 2
   noun

   slag or dross left after metal is smelted or ore is reduced

   The workers separated useful metal from the scoria beside the furnace.

From Middle English, through Latin scoria, from Greek skoria 'slag or dross', based on skor 'dung'. The contemptuous source image suited the waste left by smelting; the geological sense was later applied to rough, cindery lava.

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