Heart of the Visorak

The "Heart of the Visorak" was a golden crystal that had something to do with the Visorak. Pohatu and Onua found this artifact as part of the Toa Nuva's quest to awaken Mata Nui. When placed on the ground, it summoned all Visorak to it's location.

Dwellers in Darkness
In the Dwellers in Darkness story, the Order of Mata Nui agent known as Johmak gave the heart of the Visorak to The Toa Mahri. She told them to take it to the island of Artidax and place it in the ground. Doing this would summon every Visorak in existence to the island and the species would be wiped out as one of Artidax's many volcanoes erupted. Jaller, Hahli and Nuparu took the heart to Artidax. When they arrived, Takadox, who had been resisting on the island for a period of time, attacked them and put them in a trance. He then abandoned them and stole their boat. The Toa were saved by Makuta Teridax. They then managed to escape as the volcano erupted, wiping out the Visorak.