When the calamity that created teh Grand Scar happened it was through the southern edge of an Ocean. The Grand Scar carved a massive canyon to the mantle and the ocean was drained into underground fissures. Respressurized and superheated some of this water makes it way back up through steam-fissures in the Fissure-Rock Wasteland.
Left behind after the water left the ocean was decay and over time this decay mineralized into a top crust of the Spice. Undiscovered so far The Spice is a mineral combination that can be filtered to create reality warping elixirs.
The Spice Elixir. These Elixirs can change things. Powerful in essence those who control the Spice could potentially control the world. Reality-Warping Elixrs can be used to transport the imbiber to any location on any world at any time. Reality-Warping Elixirs can be used to increase attributes or learn free-use spells. Reality-Warping Elixirs can be used to make temporary conditions permanent.