volcanic glass
noun
1.
a natural glass produced when molten lava cools very rapidly; obsidian.
Origin
1830-40
British Dictionary definitions for
volcanic glass
volcanic glass
noun
1.
any of several glassy volcanic igneous rocks, such as obsidian and pitchstone
volcanic glass
in Science
volcanic glass
Natural glass produced by the cooling of molten lava too quickly to permit crystallization. Obsidian is a type of volcanic glass.