Bedrock

Bedrock is commonly referred to as Adminium, Admin Blocks, Adminite, and several other variations. It is a block that was first seen in Creative mode 0.0.20 as a layer surrounding the edges of a map. It later became a place-able block when Creative multiplayer was released.

In Creative Multiplayer mode, Bedrock can only be placed by Ops. It is placed by using the /solid command, and then placing Stone block. A few moments after placement (could be longer if there is lag), the stone will turn into bedrock. Non-op players cannot destroy bedrock, so it is used in making Spawn Jails, op only rooms and holding tanks for fluids. Since bedrock is not directly placed, it doesn't appear in the block selection menu. As with any blocks that aren't in the block selection menu, attempting to place one by means of hacking will cause the server to automatically kick the player. Bedrock could not be destroyed if it was in a map being played in single player. Bedrock appears a few blocks below the ocean and extends endlessly under it. It makes the edges of the map below the ocean and the bottom edge of the map. It is impossible to place blocks on the bedrock walls, but they can be built up to it by building off of existing blocks.

In Infdev and Alpha mode, a rough and uneven layer of bedrock exists at the bottom of the map. It is possible to find a hole in the bedrock and jump literally, out of the bottom of the map, although doing so will kill the player. The bedrock is impossible to destroy with any means. Bedrock can be given to players in Survival Multiplayer using the /give command. It is inadvisable to do so, considering the blocks will be placed permanently, unless Map Editing is used.

In Indev, if the bottom Bedrock layer of the map was exposed, it would be covered in lava after saving and reloading the map.