• Necklace of Unerring Mettle
• Item Level 226Disenchants into:
  [Abyss Crystal]: 1-2
• Binds when picked up
• Neck
• +63 Strength
  +94 Stamina
• Requires Level 80
• Equip: Increases defense rating by 42.
  Equip: Increases your shield block rating by 28.
  Equip: Increases the block value of your shield by 42.
• Sell Price: 7 56 23

Source

This item can be found inside Cache of Living Stone after defeating Kologarn in the 25-man version of Ulduar.

Patch changes

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

External links

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