Ebony and Obsidian

Ebony adjective - Having the color of soot or coal.

Obsidian and ebony are semantically related In some cases you can use "Obsidian" instead an adjective "Ebony".

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

Ebony and obsidian are semantically related in black topic. Sometimes you can use "Ebony" instead an adjective "Obsidian", if it concerns topics such as dark.