Anvil

An Anvil is an upcoming block that is expected to be in 1.4. It will be used for the new item repair interface. When placed above air it will fall. It will also inflict damage when dropped on players or mobs. Damage amount depends on fall altitude. Anvil-related death message is "Player was squashed by a falling anvil". If it lands on a transparent block (like torches, rails, etc.), it will destroy that item instead of dropping itself as an item like sand and gravel do. Also, it will sink to the bottom of water and lava.

Anvils can be mined with a pickaxe, they are immune to TNT.