• Mjolnir Runestone
• Item Level 226Disenchants into:
  [Abyss Crystal]: 1-2
• Binds when picked up
• Unique
• Trinket
• Requires Level 80
• Equip: Improves critical strike rating by 102.
  Equip: Your melee and ranged attacks have a chance to increase your armor penetration rating by 612 for 10 sec.
• Sell Price: 11 39 40

Source

This item can be found inside Cache of Storms after defeating Thorim on hard mode in the 10-man version of Ulduar.

Myth

Mjolnir is the name of Thor's magical hammer in Norse mythology.

Patch changes

• Patch 3.1.0 (14-Apr-2009): Added. 
  

External links

• Battle.net (EU)
• Wowhead
• Thottbot
• WoWDB