Obsidian and Scoria

Obsidian noun - Acid or granitic glass formed by the rapid cooling of lava without crystallization; usually dark, but transparent in thin pieces.

Scoria and obsidian are semantically related in volcano matter topic. In some cases you can use "Scoria" instead a noun "Obsidian".

Scoria noun - The scum formed by oxidation at the surface of molten metals.

Obsidian and scoria are semantically related in volcano matter topic. Sometimes you can use "Obsidian" instead a noun "Scoria".