The Dark Crystal, or Zedd Crystal, was a crystal from Mighty Morphin Power Rangers: Revisited which grew with negative, dark energy. It was the source of Lord Zedd's power, and Rita married Zedd in a sham wedding all in an attempt to to claim its power for herself. It is the United Alliance of Evil's equivalent of the Zeo Crystal and equals it in strength and power.
Alpha was turned evil by a windfall of energy produced from this crystal, appearing as a swirl of Dark Power around him. However, while the crystal's energy strengthened Alpha, it also hurt him as well, evidenced by the little robot sporadically coming in and out of Rita and Zedd's control.
Eventually the Dark Crystal and its power was purified and merged into the Zeo Crystal, making the latter more powerful than before.
Long after Alpha was purified and rejoined the Rangers, Rita and Zedd gave a small piece of Dark Crystal to the young robot as a present. Its negative energy was mitigated somewhat.
When Lord Zedd first arrived on Earth, he intended to let the crystal's power grow enough to open the Dark Gate and allow Angel Grove and the whole world to be destroyed. In the past, Rita wore earrings made of this crystal.
Abilities and powers
In the Moon Palace, the Dark Crystal was in the very heart of the palace, powered by a reactor that greatly strengthened its evil. The Crystal also acted as a key to open the Dark Gate. Dark Alpha attempted to fully harness and channel its vast amounts of dark energy into himself to finally obliterate the Power Rangers.
Zedd and Ninjor both said that the crystal rivaled even the supremely powerful abilities of the Zeo Crystal itself and it possessed the power to dominate everything.
The Dark Crystal produces a distorted darkness. If left unchecked, it could completely obliterate a planet into nothingness.
As a crystallized stone of pure evil, it has complete power over the element of darkness and is capable of projecting supremely strong and destructive bursts of evil energy, leaving destruction and decay in its wake, as opposed to the Zeo Crystal's ability to leave behind life and purity. It also has the ability render anything or anyone directly linked with the Zeo Crystal itself utterly defenseless and powerless if left unchecked.