Barrier

The Barrier is an invisible block added in 14w05a. The block appears transparent, but does not act as a transparent block. Buttons, redstone, ladders, ect. all can be placed on the block. The block in the player's inventory shows up as a red box with a slash through it, but when placed is completely see-through.

Trivia

 * The block, when broken in creative mode or punched in survival, will show lava particles. This does not occur with the fall particles.
 * The block, like Bedrock and Command Blocks, cannot be pushed by pistons and can not be destroyed without creative.
 * On fancy graphics, the game renders shade in a wall of Barriers.
 * This block was tweeted about by Grum