I've found some red ore in surface Crimson area, which I assumed to be Crimtane.
I've managed to mine Crimtane ore underground with my Platinum Pickaxe, but this time I was unsuccessful. What is this ore and how to mine it?
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What you've got there is Crimstone, not Crimtane. You'll need a Nightmare or Deathbringer pick to mine that.
You could also use explosives, or Purification Powder will turn it into normal stone.
Crimtane Ore, same as Demonite, can be mined with gold/platinum pickaxes. The Crimstone (entirely different from the ore) itself, requires a Nightmare pickaxe (demonite) or the Deathbringer Pickaxe, which is the one made from Crimtane ore.
Sorry I'm late but that's Crimstone. You'll need a Deathbringer, or Nightmare pickaxe to break it. If you need it to be moved, not mined, you can use explosives or purification powder sold by the Driad, (for 75 copper) and turn it to stone and then you can mine it.
Like already said... That's crimstone it can be mined with the deathbringer or Nightmare pickaxe. Or do as I did when I couldn't mine it with my copper pickaxe, and blow it up, also you can use the hallowed powder (don't know the name off the top of my head) to turn it stone! I hope I helped.
I know I'm a bit (A LOT) late.