Bedrock

Bedrock, otherwise known as Adminium or other variations, is both an indestructible and unmineable block. The primary function of bedrock is to create impassable barriers, both at the bottom of The Overworld and at the top and bottom of The Nether. It can also be found at the sides of The Nether in the Xbox version.

Properties
Bedrock appears as a black and gray charcoal pattern, and emits a dark particle effect.

Bedrock is impossible to obtain without mods or Creative Mode. If placed on ground or objects, it can never be removed without using mods or Creative Mode. Bedrock blocks are not affected by pistons.

In SMP or if the "cheats" option is turned on, Bedrock blocks can be obtained by using the /give command, but they cannot be removed once placed without creative mode.

Survival mode
It is a common myth that Bedrock can be destroyed by a sufficient quantity of TNT. While Bedrock does have a finite damage resistance, there is no explosive in the game with that much force (the average block having a resistance of 15-30). Notch confirmed on the 11th of February 2011, during a Machinima Live stream, that it is indestructible, or so solid that the amount of TNT it would take to destroy it would more than certainly crash the game, therefore the save file would show no evidence of the explosion ever happening.

It is impossible to break Bedrock by hitting it. Bedrock has "hardness" of -1. A negative hardness is handled separately in the code, wherein damage from players' hits to the block are zero, thus the accumulated damage will always stay at 0.

In Pocket Edition, if you activate a nether reactor on a low enough layer, the last layer of bedrock is replaced with netherrack, allowing access to The Void in survival.

Creative mode
In Creative mode, bedrock can be destroyed in one hit, just like any other block. By doing this, the Player is able to enter The Void, but will die (after falling past Y= -63), unless they are flying. This is one of the two ways to die in Creative Mode, aside from the  command. Bedrock is still impossible to break via TNT in Creative mode. Bedrock can catch on fire.

In the Xbox 360 Edition version of Creative Mode, Bedrock can still be destroyed, however the final layer of Bedrock cannot be broken.

Location
In Survival Mode, Bedrock comprises much of the bottom-most 5 layers of an Overworld map, and both the top and bottom 4 layers of The Nether. It generates in a very rough pattern in both the Overworld and The Nether.

In the Overworld, there are actually 5 layers even though it seems as though there are 4, due to the 4th layer being predominately flat bedrock with no gaps, which makes the very bottom 5th layer inaccessible. The game code numbers the lowest layer of Bedrock as layer 0, and the highest as layer 4.

At the top of the Nether, bedrock prevents you from going past layer 127 without making use of mods or glitches. Mushrooms will occasionally spawn on top of this Bedrock layer. In The End, defeating the Ender Dragon spawns a portal with a Bedrock frame. A single piece of flaming Bedrock also appears underneath Ender Crystals.

Classic properties


In Singleplayer Survival Mode, Bedrock is impossible to place without a mod, because Bedrock is never directly placed. But, using a server command on multiplayer, other blocks can be changed into Bedrock. Any Bedrock that exists on the map cannot be destroyed by the player.

In Multiplayer mode, server operators can place Bedrock blocks by using the "/solid" command. When /solid is used, stone blocks turn to Bedrock a short time after being placed. If /solid is used again, stone blocks placed will remain stone blocks. Normal players cannot place Bedrock; this makes Bedrock useful for making spawn jails. However, ops can destroy Bedrock like any other block, as a flag is set on the client when they log in. Vats of fluid blocks (water and lava) are also recommended to have Bedrock barriers so as to prevent server floods. Bedrock is used as a dark colored building material for normal structures as well.

A player can use an inventory editor to put Bedrock blocks in their inventory. If they attempt to place the blocks, the server will automatically kick them, even if they are an op. This is an anti-griefing features scripted into server software.

In all Classic maps, the very edges of a map are lined with a Bedrock-textured barrier. This barrier is not actually made of Bedrock blocks; it is simply a flat, impassible wall with the Bedrock texture. It is also completely covered in water. Consequently, attempting to place blocks on it does not work; you must place a block on one already attached to the wall. This barrier appears on the sides of a map starting two blocks below ocean level, extends under the ocean, and across the entire bottom of the map. Additional walls made of Bedrock blocks are often built against the ocean to prevent flooding in custom servers. Using a /kill command for classic servers causes your player to go extremely far away from the map and to glitch high above the bedrock area. The command is highly glitchy, somehow being able to send you off the map.

Trivia

 * TNT minecarts will immediately explode once hitting bedrock, even if not primed.
 * The Bedrock texture is modified from Stone, at a higher contrast and placed on all sides.
 * In Minecraft: Pocket Edition, Bedrock has a second form defined in the code as Invisible Bedrock. The Invisible Bedrock is the unbreakable void-like block that surrounds all four sides of the world. This block does not use the Bedrock texture.
 * The void fog doesn't shorten visibility when sunlight makes its way to Bedrock layer.
 * Going past the Bedrock barrier into The Void will cause you to lose 2 hearts approximately every half second once you reach below Y=-63, and will quickly kill you, even if you're on Peaceful. However, by hovering above this point using fly mode, you are able to move around underneath the world without injury, but no blocks can be placed under layer 0.
 * In maps generated before the Halloween Update, there were occasional gaps in the bottom layer of Bedrock that the player could fall through.
 * Redstone was previously unable to be placed on Bedrock; this was changed sometime in Beta.
 * In Classic, when you walk on Bedrock, it makes no sound. After if you walk on it for a while, and walk onto another block like stone or grass, the walking sound will rapidly play until you get off of the block or you wait for a while.
 * It is possible, but rare, for ore to be found encased in Bedrock.
 * On the Xbox 360 Edition, you cannot access the void in the Overworld or the Nether, as the bottom layer of bedrock is unbreakable even in creative mode. However, layers above this can be broken. This means the void can only be entered in the End.