Melange
Melange is the name of the fictional drug (also known as  spice) central to the Dune series of science fiction novels by Frank Herbert, and derivative works.

# Origin
In Dune, there is only one source of melange: the sands of the planet Arrakis, colloquially known as Dune. Melange is a geriatric drug that gives the user a longer lifespan, greater vitality, and heightened awareness; it can also unlock prescience in some subjects, depending upon the dosage and the consumer's physiology. Its use to enhance prescience makes interstellar travel possible. Melange is the most essential and valuable commodity in the universe. Its flavor strongly resembles that of cinnamon; however, each subsequent tasting reveals a different flavor.
A pre-spice mass is the precursor of melange; the mass is formed by the chemical alterations induced in water collected underground by sandtrout, the haploid forms of sandworms (although, it must be noted that some researchers have compared the spice, in its biological function among the sandworms, to sperm). These chemical processes produce gases, which build up until the mass explodes in what is known as a spice blow. This explosion kills most of the larvae and releases the melange onto the surface of the desert. Liet-Kynes describes one in Dune:
Then he heard the sand rumbling. Every Fremen knew the sound, could distinguish it immediately from the noises of worms or other desert life. Somewhere beneath him, the pre-spice mass had accumulated enough water and organic matter from the little makers, had reached the critical stage of wild growth. A gigantic bubble of carbon dioxide was forming deep in the sand, heaving upward in an enormous "blow" with a dust whirlpool at its center. It would exchange what had been formed deep in the sand for whatever lay on the surface.
Baron Harkonnen also witnesses one in the first chapter of Brian Herbert's House Atreides.
Collecting the melange is hazardous in the extreme, since rhythmic activity on the desert surface of Arrakis attracts the worms, which are four hundred meters in length on average, and very dangerous, capable of swallowing a mining crawler whole. Thus, the mining operation essentially consists of vacuuming it off the surface with a harvesting machine until a worm comes, at which time a carry-all aircraft lifts the mining vehicle to safety. The Fremen, who have learned to co-exist with the sandworms in the desert, harvest the spice manually for their own use and for smuggling off-planet.
Spice is in general use all over the universe, and is a sign of wealth. To ingest it is the ultimate display of conspicuous consumption. The planet Arrakis is central to the inhabited worlds of the universe because it is the sole source of spice.
Later, an artificial method of producing the spice is discovered by the Bene Tleilax, who develop in secret the technology to produce melange from axolotl tanks later in the series. It was not fully successful in pushing natural melange out of the market place.

# Use
Alia Atreides notes the importance of melange in Children of Dune:
Not without reason was the spice often called "the secret coinage." Without melange, the Spacing Guild's heighliners could not move. Melange precipitated the "navigation trance" by which a translight pathway could be "seen" before it was traveled. Without melange and its amplification of the human immunogenic system, life expectancy for the very rich degenerated by a factor of at least four. Even the vast middle class of the Imperium ate diluted melange in small sprinklings with at least one meal a day.
Although it is referred to as "spice" and can be mixed with food, melange is indeed a drug in the clinical sense, its use being physically addictive and having intense psychotropic effects. Spice is also a powerful entheogen, which suitably trained adepts can use to initiate clairvoyant and precognitive trances, and access racial memory. A melange user, once addicted, is thereafter compelled to continue using it for the rest of his or her life, as any discontinuation of its use will induce excruciating withdrawal symptoms, and if not quickly resumed, will invariably be followed by death.  Taken daily, however, melange can extend its user's lifespan by hundreds of years. Due to its rarity and value, and its necessity as a catalyst for interstellar travel, the group controlling spice production on Dune controls the fate of the Empire, a form of hydraulic despotism. Melange serves as the axis about which the human universe turns, it being required for space travel, and with most elites addicted to (and living much longer because of) the drug.

## Use by navigators
The Navigators of the Spacing Guild depend upon melange for the heightened awareness and the prescient ability to see safe paths through space-time, allowing them to navigate the gigantic Guild Heighliners between planets. They exist within a cloud of melange in a tank; this extended exposure warps their bodies into a grotesque neotenic parody of a human fish.

## Use by Bene Gesserit
The Bene Gesserit use "spice essence", the toxic substance that can be converted to melange, for the ritual known as the Spice agony, an ordeal in which an acolyte deliberately imbibes a massive overdose and confronts her inner-self and the selves of all her female ancestors. If she masters the confrontation, she emerges as a Reverend Mother, a Bene Gesserit of terrifying abilities, fully in command of her Other Memories, the collective egos of her female ancestors. The process is fatal to those not strong enough. It is said that no male has ever survived this process other than Paul Atreides and his son, Leto II.

# Physiological side effects
Extensive use of the drug tints the sclera, cornea and iris of the user to a dark shade of blue, called "blue-in-blue" or "the Eyes of Ibad," which is something of a source of pride amongst the Fremen and a symbol of their tribal bond. Paul Atreides, the main character in the original Dune novel, initially has green eyes, but after several years on Arrakis his eyes begin to take on the deep, uniform blue of the Fremen. On other planets, the addicted often use tinted contact lenses to hide this discoloration. In Dune, Paul sees two Guildsmen and notes:
The taller of the two, though, held a hand to his left eye. As the Emperor watched, someone jostled the Guildsman's arm, the hand moved, and the eye was revealed. The man had lost one of his masking contact lenses, and the eye stared out a total blue so dark as to be almost black.

# Quotes
- "He who controls the spice controls the universe."
- "The spice must flow."
- "In this time, the most precious substance in the universe is the spice melange. The spice extends life. The spice expands consciousness."

# Notes
-  In Children of Dune it is noted that "Farad'n touched his own eyelids, feeling the hard surfaces of the permanent contact lenses which concealed the total blue of his spice addiction."
-  In Heretics of Dune, the Bene Gesserit Schwangyu notes that "Blue-in-blue eyes uncorrected by any lens gave Lucilla a piercing expression that went with her long oval face." Herbert later writes of Duncan Idaho that "His first glimpse of Schwangyu had confronted him with eyes concealed behind contact lenses that simulated non-addict pupils and slightly bloodshot whites."