Cobalt Ore

Cobalt Ore is a Hardmode ore that appears in the world when the player destroys a Demon Altar with a Pwnhammer. This will "bless" the world with deposits of either Cobalt, Mythril, or Adamantite Ore. These ores can then be found randomly throughout the Underground and Cavern layers. Cobalt Ore can only be mined with a Molten Pickaxe or better. It is immune to all types of explosions. It is the most abundant of the three hardmode ores.

Trivia

 * Actual Cobalt is a poisonous, magnetic metal (though it is actually a key part of vitamin B12, which is necessary for living beings and has extremely low toxicity).
 * Cobalt is named after the Kobold, at that time thought of as a mischievous spirit.
 * Pure cobalt is an element found on the periodic table just after iron, and is actually silver-like in color. However, cobalt is never found pure in nature. Its historic primary use was as a pigment used especially in glass or porcelain, as it turns a rich "cobalt blue" when in the compound form of Smaltite, made of cobalt, iron, and nickel combined with Arsenic. This made cobalt, along with lapis lazuli, one of the few mineral blue pigments, and therefore was historically an extremely valuable commodity.
 * Several Cobalt items in the game are Japanese-themed, namely the Cobalt Naginata, Cobalt Armor and the Cobalt Sword which resembles a katana.