Dark Gems

The Dark Gems (ダーク・ジェム, Dāku Jemu) are a powerful, sinister, corrupted version of gemstones which can be used as a violent weapon and explosive. As gems represent part of the good side which can be useful of making energy sources, they represent part of the evil side by negatively affecting anything the Dark Gems comes in contact with. Potent little balls of wickedness, even the smallest particle of Dark Gems can corrupt any amount of regular Gems. The Dark Gems can be used for a number of deadly uses such as increasing one's power, sucking out the light and goodness from the world, contorting its contacted area into a putrid, scary den just right for a villain's domination, reviving the dead, corrupting any sort of life forms and even weakening some.

"It is said that no one can harness or control Dark Gems! They and their corruptive substances dominates and destroys everything it touches!"
 * —Kaos, talks about the Dark Gems.