Crimtane Ore

Crimtane Ore is a rare pre-hardmode or that was added in par with Demonite Ore in the 1.2 update. It is a luminescent blood red color and can easily be spotted underground. It is extremely rare in the undeground, but much like demonite, it is easily spotted due to its glowing effect. It can be found more commonly in the Crimson Biome's Chasms.

Crimtane is extremely rare so it is not recommended that the player goes mining for it. Rather summoning the Brain Of Cthulhu and grinding it for Crimtane Ore and Tissue Samples. Both of which are used in the creation of Crimtane Armor and coinciding tool kit. The easiest way to summon the Brain Of Cthulhu is to craft the Bloodied Spine from 15 Vertebrae (dropped by the Crimson Mobs). Another easy way is to smash 3 Demon Hearts found in the Crimson Chasms, which much like the Eater Of Worlds, will summon the Brain Of Cthulhu.

History
It's ore from the crim and dropped from differend bosses,including brain of Cthulhu.