Adamantite Ore

Adamantite Ore is an ore that is added to a world as a reward for "purifying" it. It is used to craft the Adamantite Forge and Adamantite Bars, therefore, it is the basic ingredient for all Adamantite items. The ore will not appear in the world until the player destroys a Demon Altar with a Pwnhammer. This will "bless" the world with deposits of either Adamantite Ore, Cobalt Ore, or Mythril Ore. These ores will then be found randomly like any other.

It is colored red and seems to be found in the Cavern level. You need to have Mythril Drill to be able to mine it.