Ender Portal Frame

Ender Portal Frame is a block that can be found in strongholds as of Beta 1.9 pre-release 3, but was unfunctional until pre-release 4. The Ender Portal blocks have a decorative bluish-green top, while the sides and bottom are an off-white color. The sides are also decorated with the same color used for the top. Using an Eye of Ender on the block inserts an eye to the top of the block. Once an Eye of Ender has been inserted in all 12 Frame blocks, then the Ender Portal will activate and the player can pass through to access The End.

They are found in a ring shape within a room over a pool of lava and a staircase containing a Silverfish spawner. Some of the portal frame blocks already have Eyes of Ender in them (usually three), while the rest do not.

Trivia
This is especially noticable when it gets dark.
 * The frame block cannot be moved using pistons.
 * Portals are often "guarded" by silverfish spawners.
 * Redstone circuits can NOT be passed through frame blocks.
 * Using the "Too Many Items" mod to place air portal block above ground, shows that the block emits a bright blue glow.

History
The Ender Portal Frame used to have a different texture, emitted a light level of 15 and was non-solid block when cracked, becoming solid when repaired. Although it couldn't be mined, an explosion caused them to drop as an item shaped like a Glass Pane. They had no tooltip, indicating that them dropping at all was a bug. The player had to repair a cracked Ender Portal Frame by right clicking it with an Eye of Ender.

On jebs livestream, it was publicized that the texture had changed from this, and instead of using an Eye of Ender to repair a block, you now need to insert all Eyes of Ender to make the portal work.