TNT

TNT is a block used to cause explosions.

Explosion Properties
Upon being struck by the player, set on fire, or energized by redstone, it will start smoking and flashing white, and be subject to gravity. After 4 seconds, it explodes, damaging surrounding blocks, mobs that are nearby, and the player if they are not careful. When TNT is placed in any liquid, it will not destroy any blocks when detonated, though it still can damage mobs and the player.

The TNT blast will destroy surrounding blocks depending on the blocks blast resistance. The explosion propagates farthest through air, having a resistance of zero. An explosion in the open will create a explosion radius of about 7, and TNT immediately enclosed in stone will destroy an exact 3x3x3 cube from its center. Every block can be destroyed with TNT except for Bedrock, Obsidian, and liquid blocks.

A player or mob sitting in a minecart will take minimal damage from a TNT explosion. This can be used to make people/mob cannons.

TNT is a flammable block. When it is burned (when an ordinary flammable block would disappear and be replaced by more fire), TNT is activated. TNT which is near lava will eventually be set on fire and detonate.

Too many TNT blocks too close together might cause lag issues; however, a way to avoid this would be to spread them out to a minimum of two blocks or more.

Sand and Gravel blocks will react accordingly to a detonation, scattering from the point of origin, and will fall through the TNT when it is triggered.

Uses
TNT monster traps can be created, making TNT a powerful defensive tool. When exposed to a current, the TNT activates as if it had been activated by a player. Combine this with a Pressure Plate and you can create an automatic defense for your buildings. This method is a one-off, as the TNT needs to be replaced after each use.

For the TNT to receive the circuit's signal, the Redstone needs to be directed straight into it from at least one of four sides, from either the Layer the TNT is based on, or above or below one layer. Diagonally adjacent entry will not make a connection. Redstone next to TNT will also set off the TNT, even if it is not directly connected with it (through a T connection not directly connected, or an "I" connection running parallel alongside it). TNT will only be set off by redstone if the redstone signal it is receiving turns on. This means that if it is receiving a current when it is placed, it will not be set off, but if the signal turns off and turns on again, it will be set off. There is however a bug where after flipping the signal off, sometimes only a few of the TNT blocks will become active. Redstone torches will activate a TNT block as well if directly under the TNT block, or under a block on which the TNT rests.

Because primed TNT is affected by physics, it is used as a projectile which is propelled by an explosion of a TNT charge in TNT Cannons. Also, Arrows attached to TNT will fall off when it becomes a primed TNT. This can be used to create arrow traps.

It is possible to 'rocket-jump' via TNT, by jumping while standing on it just before it explodes. However, this may deal damage, and possibly kill you.

Mining
Mining using TNT might be faster than mining by hand but it is impractical for gathering resources; about 70% of the blocks are completely destroyed in the process. Nevertheless, TNT can be a part of efficient mining techniques - as the means of removing unneeded layers of blocks and exposing underlying layers. It can also be used for clearing large volumes for underground building projects.

Still Water and Lava, Obsidian and Bedrock are the only materials that will resist a TNT explosion. They CANNOT be destroyed with more than one block of TNT. If one block of TNT directly adjacent to a block cannot destroy the block, no amount of TNT can.

Water as blast controller
If a layer of water is spread between a destructible block and an explosion, the block will be protected. A one-block-thick water screen will stop most explosions from reaching the other side, however, a player laying multiple blocks of TNT should mind the placement of the explosives, as primed TNT entities may launch each other through the water screen. Using water this way let you use TNT near an important area, such as a house, base, or ore vein.

Thus, a player can use this to dig a big quarry or hole precisely and quickly by placing an "curtain" of water on the extremities of said hole and dynamiting the center.

Removal
Removing TNT can be tricky, and varies by game. In Survival Test, hitting it two times would stop the countdown and cause the TNT to revert into a resource block which could then be picked up. In Beta, there is no way to pick up a TNT after it has been placed, but it can be detonated without damaging surrounding blocks by immersing it in a liquid. This explosion would still damage a player or a mob.

Primed TNT
A primed TNT is an entity in Minecraft world. It is spawned at the center (+0.5,+0.5,+0.5) of a destroyed TNT block, while itself is a cube with an edge length of 0.98. Its fuse lasts 80 ticks if struck or activated by redstone, or a random number between 10 to 30 ticks if it's destroyed by an explosion.

Once spawned, the primed TNT is given a vertical velocity of 0.2 m/s, and a horizontal velocity of 0.02 m/s in a random direction between east and north. This directional bias towards north-east is due to a bug. If it does not collide with another block, it will travel 0.166m horizontally on flat ground before it stops and explodes. A primed TNT can be lit on fire in the same manner as arrows can, but it does nothing.

Trivia

 * The name "TNT" (short for Trinitrotoluene) is technically incorrect. Visually, the block resembles a collection of sticks of dynamite, which is an entirely different explosive frequently confused with TNT. The crafting recipe for the TNT block references the manufacture of dynamite, which is made by stabilizing nitroglycerin with an absorbent material such as sawdust or earth. However, gunpowder is not a component of either explosive.
 * There are some traps in which the player suspends TNT over a 1x1 long pit and activates it. It will drop into the darkness, hopefully killing any unwanted monsters below it. It is especially useful upon entering a dungeon away from the chest to destroy the monster spawner.
 * An activated block of TNT will fall 77 blocks before exploding
 * In the lastest update for minecraft TNT can not have torches placed on it. Any torches placed previously will go away

Gallery
TNT TNT