6 obsidian makes 3 obsidian doors. The doors can only be broken with a diamond pickaxe and are explosion proof. Like an iron door, they can only be opened with redstone. Obsidian doors could be useful for security. You could build obsidian vaults only openable from the inside. I want this to be added because right now iron is the strongest door and it can easily be broken with any pickaxe. Obsidian doors would fix this problem and allow better security for your stuff.