Lunar Crystals are spawned during the fight with the Titanic Guardian in the Chamber of the Moon^{[33.8, 18.8]}

in Uldum during the quest I'll Do It By Hand. Killing all three of them will kill the Guardian.

Patch changes

• Patch 4.0.3a (2010-11-23): Added 
  

External links

• Wowhead
• Thottbot
• WoWDB