Illium-629 was a by-product of the decrystallization of dilithium. (TNG episode: "Pen Pals")

In 2386, the USS Robinson discovered a vessel in the Gamma Quadrant that had been attacked by the Glant and disabled by the dead zones in the null space around their territory. The vessel's dilithium decrystallized and illium 629 was created. (DS9 novel: Original Sin)

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