Minecraft wiki entry for Block_of_Copper, associated text: In Java Edition, these additional blocks are chosen by random walks as follows: The position of the struck copper block is set as the start point. Then, the game performs 3 to 5 walks. In the beginning of each walk, a judgment point is set at the start point. For each step of the walk, the game randomly selects 10 blocks from a 3×3×3 volume centered on the judgment point. If an unwaxed copper block is found among these 10 blocks, the judgment point is transferred to the first such block found, and 1 oxidation layer of that block is removed (if the block is still unoxidized, the block stays as it is). The number of steps in a walk is between 1 and 8 (inclusive), chosen randomly for each walk. This means that one single lightning strike can deoxidize up to 41 blocks (1 block initially struck by lightning + 5 max walks*8 max steps in every walk).[3]