Nether Reactor

The Nether Reactor is a structure built using a Nether Reactor Core, which is a block exclusive to the Pocket Edition.

Crafting
Crafting the Nether Reactor Core requires three diamonds and six iron ingots.

Nether Reactor
The Nether Reactor is built with a nether reactor core, gold blocks, and cobblestone, arranged in the following configuration:

Note the block in the center of the middle layer represents the Nether Reactor Core.

Top layer:

Middle layer:

Bottom layer:

When the Nether Reactor is built and the core activated, it generates a room of Obsidian (7x17x17)with some openings, around the reactor called a "Nether Spire" (Unofficial name) The reactor itself will turn into a new block called Glowing Obsidian resembling Netherrack, and it will start spawning various items and blocks, such as Gold, Melon Seeds, Paintings, Glowstone Dust, Doors, Mushrooms, Bones, Cacti, Arrows, Feathers, Bowls, Sugar Cane etc, as well as Zombie Pigmen. After it burns out, there will be a massive obsidian structure with multiple floors.

The Nether Reactor only lasts around 45 seconds. During the 45 seconds the Reactor is active, it is difficult to escape the room, as it is all obsidian.

Trivia

 * The Reactor does not function in Creative mode; this is intended.
 * The reactor's structure was originally iron and gold blocks rather than cobblestone and gold, but this was changed due to its cost and the fact that the reactor turns into obsidian except the core.