volcanic glass
nounUK /vɒlˈkænɪk ɡlɑːs/
US /vɑːlˈkænɪk ɡlæs/
Volcanic glass is a shiny, smooth rock that forms when hot lava cools very fast.
The museum had a piece of volcanic glass that looked like black jelly.
OTHER MEANINGS
2. A type of glassy rock formed from rapidly cooled magma.
Scientists studied the volcanic glass to learn about the eruption.
3. Obsidian used in ancient tools and weapons.
Early people made sharp blades from volcanic glass.
4. A material that can be polished to a shiny finish.
The jeweler polished the volcanic glass into a pendant.