Corrupted Kor Gem

Kor gems were usually used by some spellcasters to hold energy for their magics. Corrupted Kor Gems were such gems imbued with evil power by the naga. These corrupted gems could eventually be purified but were made weaker in the process.

Source
This item dropped from naga outside Blackfathom Deeps in Ashenvale.

As a quest objective

 * Seeking the Kor Gem
 * The Path of the Adept