The Firseid Sandbox
A clear quartz-like ball with an extremely powerful anti-magic effect
The meteor heart was originally found in the center of the massive asteroid that was carved into the City of the Dead. Hundreds of millions of years ago the asteroid collided with Firseid and left a rift between planes. Even after such an unimaginably immense time, the rift left a scar on the world — the Great Eastern Desert.
The clerics in the City of the Dead were using the Heart to weaken the Phoenix and imprison it. The party obtained the heart when the rescued the Phoenix.
The Heart is immensely powerful under certain circumstances … and the Phoenix told the party that it’s even capable of being used to completely sever their world from magic.