Any of various minerals (such as obsidian and tachylite) that resemble glass in their appearance and amorphous structure, having solidified from magma too quickly to crystallize.
Origin
Mid 19th century; earliest use found in The Spectator.
Definition of natural glass in US English:
natural glass
noun
Any of various minerals (such as obsidian and tachylite) that resemble glass in their appearance and amorphous structure, having solidified from magma too quickly to crystallize.
Origin
Mid 19th century; earliest use found in The Spectator.