Spice

Spice, also known as melange, is the most expensive substance in the Known Universe, granting longevity, immunity to certain poisons and diseases, and people with predespositions the ability to awaken their prescience. One of the early side effects of spice consumption are blue-within-blue eyes, also known as the Eyes of Ibad.^[1]

Lore

Arrakis is the only planet where spice can be found.

The Spice Cycle:

The cycle begins with microscopic sand plankton, which feed on melange scattered when sandworms die.^[2]
These plankton eventually grow into sandtrout, leathery, slug-like larval forms. Their primary role is to seek out and encapsulate water deep underground, as water is lethal to adult sandworms.^[3]
As sandtrout gather around water pockets, their fungal excretions mix with the water. This creates a volatile pre-spice mass that produces high levels of carbon dioxide gas.
Eventually, the gas pressure becomes so extreme that it triggers a massive underground explosion called a spice blow. This erupts to the surface, scattering the pre-spice material across the sand. Millions of sandtrout are killed in this event.^[4]
Once exposed to the sun and air of Arrakis, the pre-spice mass dries and undergoes a chemical reaction to become the revered Spice Melange.
The few sandtrout that survive the explosion enter a dormant state for several years before emerging as small, juvenile sandworms. Over centuries, these grow into the massive Shai-Hulud, continuing to patrol the desert and spread more plankton to start the cycle anew.