Bedrock
Bedrock, is a completely indestructible and unmineable block, impervious to all explosives and tools. The primary function of bedrock is to create an impassable barrier at the bottom of The Overworld and at the top and bottom of The Nether. Bedrock appears on the very bottom 5 layers of a map and also at the top and bottom 4 layers of The Nether, in a very rough pattern. When you defeat the Ender Dragon a portal with a Bedrock frame appears. A single piece of Bedrock will appear after destroying an Ender Crystal, sometimes on fire.