Block  is a type of block in the Mario series. In Super Mario Bros. Blocks (the "used" ones) usually appear when 
Used Block Artwork - Super Mario 3D World
Mario hits a Question Block or Brick Block with an item or a coin inside, though they sometimes are naturally Blocks. Blocks are usually square and brown with rounded edges and nails. In Super Mario World, Blocks have small, closed, angry eyes, and if the player hits a blue P-Switch, all Blocks turn into coins and vice versa for a short time. Blocks can only be broken by Mega Mario or stronger enemies, such as Broozers.