It is the baseline material used in race synthesis.  A cross-section of Azeroth's crust was used as the foundation for the Earthen's synthesis rather than the typical biomass construction foundation used by the Creators.$B$BResearch on the world's composition led the Creators to theorize that an enhanced being could be synthesized that would epitomize the resiliency of this world's essence.  This was accomplished by choosing to use a blend of Azeroth's various stone core compounds as the foundation.