Unstable Rift Crystal

Unstable Rift Crystal used to be the "shortcut" entrance to Molten Core in Blackrock Mountain. It used to be located left of Lothos Riftwaker. It existed as an alternative to the window shortcut added in patch 1.3.0.

It was only usable if one had completed the quest Attunement to the Core, the attunement quest for Molten Core. When Lothos Riftwaker gained the ability to teleport players himself in patch 1.11.0, the crystal was removed.

Quotes
You see large cavernous tunnels and corridors reflected inside the crystal. You recognize the area as the Molten Core.
 * Gossip