By 2506, the xel'naga temple on Shakuras used zenith stones to regulate its energy. When the protoss decided to overload the temple's energies to destroy Shakuras, they were required to destroy the stones to do so.
The player must destroy the zenith stones to be able to overload the temple. This can be done at any time before or after the zerg counter reaches the objective amount, but the player cannot overload the temple if the stones are not all destroyed, and so the mission cannot be won.
As a zenith stone loses health, it begins regularly zapping units near it with psionic energy, dealing 10 damage. At lower health it casts psionic storms freely. When destroyed, the stones exploded, knocking back and damaging units.
Zenith stones can also be found in the Co-op mission "Temple of the Past" where destroying them is a bonus objective.