This is a block which is invisible when it's first placed in the world. The player however can walk on top of it and cannot pass through it. This block is great for invisible floors and/or walls. The block will become visible when it receives a redstone signal.

Note:This block will cascade it's visibility to up to 100 other neighboring Boundary Blocks when it receives or stops receiving a redstone signal. If you place a Boundary Block next to an already visible Boundary Block you will have to turn the redstone signal off and then on again to see your new block. This is intended.

This block is created by placing an ender pearl in the middle of the crafting grid and then surrounding by glass.