Dragon Egg

A dragon egg is one of the rarest blocks in Minecraft.

Obtaining
A single Dragon egg spawns on top of the exit End Portal left by the Ender Dragon. Dragon eggs cannot be mined directly, as when trying to mine it will cause the egg to teleport. However, the egg does not teleport if there aren't any air blocks available for it to teleport to, allowing to mine it. It drops as an item when falls into a non-solid transparent block, or when pushed by a piston.

Teleporting
To cause the egg to teleport, press while in survival or adventure mode ( in creative). It teleports to a place nearby (up to seven blocks vertically and fifteen blocks horizontally), creating the same particles as Endermen. It may teleport into the air and subsequently fall to the ground.

Usage
Dragon eggs, if there is no block below it, will fall until it lands on the next available block. When it is being affected by gravity and falling, it exhibits a smooth falling animation.

Dragon eggs cannot suffocate mobs or players when falls and covers them.

Dragon eggs can be placed on a non-solid block without falling.

Light source
Dragon eggs emit a light level of 1.

Trivia

 * The writer of the Minecraft comic WonderCraft, Samcube, was requested by Mojang to create official Minecraft posters. In part of these works, one can see an area with an Ender Dragon and a chicken on top of a Huge Mushroom. In the same scene the dragon egg is visible near the chicken.
 * When hit with Flint and Steel, a Dragon Egg might break with one hit or teleport and appear in a new position, but still broken.
 * The dragon egg can be considered the rarest block obtainable in survival due to the fact that it only spawns once per world.
 * The dragon egg's side sticks out into adjacent blocks, so if it falls into a one block space, the sides will clip through the blocks.
 * The Dragon Egg uses a slightly altered Crying Obsidian texture (purple stripes instead of blue).
 * On March 13th, 2014, Dinnerbone tweeted about that he might add a Dragon Egg feature in his "Ultimate Plan", but he hasn't discussed this with the Mojang team yet.