In "Dune," the desert planet Arrakis is rich in melange, the valuable substance commonly called the spice.
Melange is a fictional drug created by Frank Herbert and is the most important commodity in the universe of "Dune." It extends life, improves vitality and awareness, and can produce prescient abilities in certain users. The Spacing Guild depends on it because its navigators use spice-induced prescience to guide ships safely through interstellar travel.
Arrakis is the only natural source of melange in the original story. Its production is tied to the life cycle of the planet's enormous sandworms, making spice harvesting extraordinarily dangerous. Mining crews use harvesters to collect deposits, then try to escape when rhythmic vibrations attract the worms. The Fremen also gather and use the spice in their daily life and religious practices.
Melange is highly addictive, and prolonged use turns a person's eyes deep blue, known as the "blue-within-blue" eyes of the Fremen. Arrakis is therefore valuable not merely for its mineral wealth, but because control of the planet means control of the Imperium's economy, politics, and space travel.