Dilithium (abbreviated Dl) is a chemical element, a transuranic metal that occurs in crystalline form. Dilithium is element number 119 on the periodic table. This element was discovered by Humans in 2049 on Jupiter V. (ST reference: Star Fleet Medical Reference Manual)
Dilithium was a rare transuranic element that was formed naturally by violent explosions or supernovas. (TOS novel: Preserver) It was the only known material which could regulate matter/antimatter reactions, which was why it is used by most species in their warp drives. Different compositions and origins produced slightly different appearances in the crystals, ranging in shape and color. Its atomic weight is 315, and its atomic number is 119. (ST reference: Star Fleet Medical Reference Manual)
Originally, the lifespan of dilithium was limited until methods were discovered in recrystallizing fractured crystals. This caused a drop in the value of dilithium, which was a precious element around 2275. (TOS novel: Preserver)
Having a large supply of dilithium almost instantly promoted a planet into prominence in interplanetary politics, as other species seek trade. Some planets known for their dilithium deposits include Coridan III, Troyius, and Avaton II. (TOS video game: Starfleet Academy - Strategic Command)
At some point in the 22nd century, the Klingon Empire mined the innermost planet of the Arhennius system to obtain its dilithium; the Federation never noticed the dilithium on its long range scans as it was under several kilometers of rock. (Star Trek novel: Engines of Destiny)
In 2254 Starfleet engineers constructing Project Pharos on the Pharos siteworld in the Marrat system discovered huge deposits of incredibly pure dilithium; of such purity that had it been mined it would not have required refining. Because Marrat was an open system Starfleet opted to keep the discovery a secret, concerned it could provoke a gold rush, or war! Unfortunately Klingon Commander Kaaj did find out about the discovery and attacked Pharos in response. When the USS Enterprise was sent to investigate why communications had been lost with Pharos Kaaj attacked the starship. To solve the dilemma Captain Christopher Pike had the Enterprise fire on Pharos, igniting the entire planet in a chain reaction, and eliminating the source of conflict. (EV comic: "The Fires of Pharos")
Romulan scientist Tavorak was reputed to have created a virus that ate dilithium and attempted to sell his creation to the highest bidder making him a wanted criminal. (TNG comics: "A Matter of Conscience...", "The Truth Elusive")
The planet Naia VII was rich in dilithium, among other valuable materials. A Starfleet Corps of Engineers mining operation there in 2368 excavated these, which were vital for Starfleet to rebuild its strength following the Battle of Wolf 359. (TNG - Assimilation² comic: "Issue 2")
During the 23rd century, the crystals often deteriorated rapidly during adverse situations, so starships often kept large supplies of them on board. (TOS video game: Starfleet Academy - Strategic Command)
During a trip back to the 20th century to retrieve two humpback whales, the dilithium crystals of the Klingon ship Kirk and his crew were using began to wear out. Since fission based nuclear reactors was still in use, Captain Spock determined that it might have been possible to obtain high energy protons from such a reactor, and bombard the crystals with them - thus causing dilithium to recrystallize. After obtaining such protons from the United States aircraft carrier Enterprise, Spock and Engineer Montgomery Scott were able to successfully recrystallize dilithium. (TOS movie: The Voyage Home)
By the 24th century, the process of recrystallizing dilithium had been refined to the point that it had become routine on board Federation vessels. Using a theta-matrix compositor, dilithium could be recrystallized inside the warp reaction chamber. (TNG episodes: "Family", "Skin of Evil")
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point of view.
Dilithium appeared as an element on the table of elements barely legible on screen in the TNG episode: "Rascals", with the chemical symbol Dt. The Star Fleet Medical Reference Manual lists it as symbol Dl. The formation of the name has the prefix di- preceding lithium, indicating a twofold increase of the basic lithium. A similar nomenclature is used for trilithium and decalithium.