scoria
/ˈskɔriə/
noun
- A dark, rough, lightweight volcanic rock full of holes, formed when lava cools quickly with trapped gas bubbles.
- Gardeners sometimes mix scoria into soil to improve drainage.
- We collected pieces of scoria near the volcano's base for our science project.
- The hiking trail was covered in chunks of black scoria from an ancient eruption.
- The waste material left after metal is separated from ore in a furnace; slag.
- Workers recycled the scoria to make cheap building blocks.
- Piles of scoria from old smelting operations still dot the landscape.
- The blacksmith removed the scoria from the top of the molten iron.