End Crystal

An end crystal, or by its entity ID, ender crystal, is both an item and an entity found in the End.

Natural generation
End crystals are found atop the many obsidian pillars in the End.

Skeleton trap horses
An end crystal will sometimes drop from skeleton trap horses after killing it.

Healing the ender dragon
Their primary purpose is to recharge the health of the ender dragon, who will charge from the nearest crystal within a cuboid extending 32 blocks from the dragon in all directions. The dragon is healed each half-second. If multiple ender dragons are spawned, an ender crystal can affect multiple dragons at the same time. The healing beam is neither obstructed nor is its power diminished by entities or blocks.

Respawning the ender dragon
As items, end crystals may be placed on bedrock and obsidian, if the two blocks above the bedrock or obsidian block are air or replaceable blocks and no other entities intersect the area. If four are placed on the end exit portal, one on each of the flat sides, the crystals will respawn the original end crystals on the obsidian pillars, as well as resurrect the dragon itself, before exploding.

Explosions
The end crystal can also be used as an explosive with the unique property of making all crystals near it explode at the same time, which can be used to quickly (after placing the crystals) blow up large areas or as an unusual trap mechanism.

When attacked, even by attacks that normally do zero damage, or otherwise damaged in any way, they will explode. The ender crystal's explosion is the same power as a charged creeper, 50% more powerful than TNT. Any ender dragon charging from the crystal when it is destroyed will take damage.

Properties
The base appears to be made of bedrock, with a crystal hovering over it. While in the End, a crystal will continually generate fire at its current position, one block above the base (directly on top of the block the base is embedded in), replacing any other block at that location. This fire is not capable of spreading. The end crystal entity is not solid and can be walked through freely. An ender dragon cannot destroy the crystal simply by going near it.

End crystals can be pushed by pistons, but if they are moved while in live fire they will explode.

Data values
End crystals have entity data which defines various properties of the entity. Their entity ID is.

Trivia

 * According to Jeb, the reason behind the current crafting recipe using glass as opposed to chorus fruit or any materials introduced in 1.9 is as a means for player to craft the end crystal in older world that the dragon has been killed already.
 * Placing water above an end crystal using a bucket will cause a looping effect, where the fire is continuously put out and reinitialized as the water attempts to flow down and is stopped. The water will not spread, as it can flow downward, but is prevented by the reoccurring fire instantly taking its place.
 * Unlike the similarly-explosive TNT, normally hitting an Ender Crystal will make it explode. However, they can be removed safely if they're immersed in water first.
 * Since fire is only checked when an entity moves, end crystals do not normally take damage from their own fire.
 * Oftentimes, the fire will stay after an end crystal blows up.