Call the earth to your defense, granting a damage shield for you and nearby allies that absorbs 722 damage. This portion of the ability scales off your Maximum Health.
You also gain Major Mending, increasing your Healing Done by 25% for 2.5 seconds.
Obsidian Shield is a skill located in the Earthen Heart (which can be found in the Dragonknight skill tree). Obsidian Shield is a base skill, and can be morphed into Igneous Shield or Fragmented Shield.