I found a recipe for an earthquake amulet in Celestia. It requires 4 Minotaur treasure cards. Now the amulet doesn't say anything about being Myth only, but the only thing I can find in the way of a Minotaur treasure card is the recipe from the myth tree, which requires you to be myth.
If you can only get your hands on a minotaur treasure card by being a myth and making one, then the recipe should only be available to myth.
So is that the case, or have I just not found the treasure cards yet?