Laurite

Laurite is the rarest ore that can be found in Mining Insanity, and the only ore classified as Mythical in-game.

Appearance
It is a black block with a Foil texture. It emits pink sparkles and fire, as well as a strong pink light.

Spawning
Laurite could only be described as ridiculously rare. Under normal conditions, its spawn rate is on the order of 1 in 3 billion, rare enough that by the time the player has found a Laurite block, the other blocks they've dug up could very well be worth more than the Laurite itself. Hunting Laurite just isn't worth your time outside the month of February. Even then, Laurite is still ridiculously rare. Your only reasonable chance to find this is to play the game all day on Valentine's Day, with no breaks whatsoever, and hope that you generate a Laurite at some point.

On any day that is not February 14th, Laurite will only spawn in the Obsidian layer (or Hellstone, where it spawns twice as often, if it's January, March, or May). On February 14th, it can spawn anywhere.