Obsidian

Obsidian is a unique pre-Hardmode Ore, which created when Water and Lava collide, at which point it forms placed Blocks that can be mined and collected. Obsidian appears as an Ore and is gathered similarly, but has no bar form of its own; though it is required in order to craft Hellstone Bars. Mining Obsidian requires a pickaxe with at least 65% pickaxe power or Explosives.

Trivia

 * Obsidian in real life is cooled volcanic glass. It is a very brittle substance that chips easily.

History
Obsidienne 흑요석 Обсидиан