Elemental Rune

Combining 300 Elemental Runes will create an Elemental Tablet.

Source
All bosses in Blackrock Foundry drop 4-10 Elemental Runes. Much like legendary quest item drops in Mists of Pandaria, the runes can only be looted from each boss once per week, regardless of difficulty, and there is no difference in drop rates between difficulties.


 * A very low chance of looting it from garrison work orders
 * Rare level 100 garrison missions (requires follower item level 645)
 * The weekly catch-up quest Work Work Stoppage added in patch 6.2.2 guarantees 75 runes a week in exchange for 20,000 Apexis Crystals.

Objective of
900 runes are required to in order to form the three tablets needed for Might of the Elemental Lords.