Mythril Ore

Mythril Ore is an ore from 1.1 update. It will likely be used to craft the Mythril Repeater, Mythril Drill, and Mythril armor. 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 Mythril Ore, Cobalt Ore, or Adamantite Ore. These ores will then be found randomly like any other. Molten Pickaxes cannot mine Mythril Ore

It is colored grayish-green and seems to be found in the Cavern layer.

Trivia

 * Mythril Ore may be a reference to the Mithril in J. R. R. Tolkien's writings.