Valadium Chunks are an ore that can generate naturally in the world's Underground and Cavern layers upon defeating Coznix, The Fallen Beholder. The generating of the ore into the world can be done up to 3 times; defeating Coznix after that will generate Lodestone Chunks or Valadium Chunks with a 50% chance of each. After 3 fights if you received the same ore each time you will be guaranteed to get the other. Additionally, defeating Coznix in Expert Mode will generate extra Valadium Chunks compared to Normal Mode. It can also be found in Scarlet Crates in Hardmode after defeating Coznix.
By default, defeating Coznix, The Fallen Beholder has a 50% chance of generating Valadium Chunks, with the other 50% chance generating Lodestone Chunks instead. After either ore has been generated 3 times, the opposite ore becomes guaranteed to generate. As a result, Coznix must be defeated 6 times in total to generate all the possible Valadium and Lodestone Chunks possible for the world.