Hellstone Bar

Hellstone Bars are bars crafted from Hellstone and Obsidian. They are used to craft some of the most powerful equipment available pre-Hardmode, and remain useful, if not necessary, in dealing with the shift in difficulty upon entering Hardmode. Notably, the Molten Pickaxe is the only pre-Hardmode pickaxe capable of mining the first tier of Hardmode ores, Cobalt and Palladium.

Crafting all items excluding the Hellfire Arrow requires 207 Hellstone Bars (621 ore and 207 Obsidian) /  192 Hellstone Bars (576 ore and 192 Obsidian) /  175 Hellstone Bars (525 ore and 175 Obsidian).

Trivia

 * Hellstone Bars have a special immunity to lava in the game's code, even though their rarity implies this anyway.