Molten Pickaxe and Nightmare Pickaxe are the only pre-hardmode picks that don't require wood to craft.
Originally, the Molten Pickaxe was made from Meteorite Bars, and was still the highest tier pickaxe. However it belonged to the Meteorite Tier. Hellstone Bars were not craftable yet and the Underworld existed but was pointless (except for money). However, this was in the Alpha version, and has been changed now.
The Molten Pickaxe has a 1 in 10 chance to set enemies On Fire. On Fire does approximately 2 damage per second.