Luxum crystals are a very rare crystal obtained from Lake Natth on Ambria. Ambria was a planet steeped in the Dark Side long watched over by Jedi Master Thon. Over the years, Master Thon was able to contain that evil in Lake Natth.
The Jedi eventually discovered that through intense meditation, one could create Luxum crystals from the tainted water of Lake Natth.
Thousands of years later members of the Shard, a sentient species of crystal discovered they could join themselves to droid mainframes and acquire locomotion. Like all forms of life, the Force blessed some individuals with a heightened Force-sensitivity. The Shard were no different and joining themselves to various battle droids, they formed what would be known as the Iron Knights.
With names an alien concept to the Shard, and no native names of their own, many adopted the names of the crystals they used in their lightsabers. One such Iron Knight used a Luxum crystal as its lightsaber's focusing crystal and subsequently adopted the same name. Sadly, Luxum was one of the many Jedi Knights who would fall to the Dark Side during the Yuuzhan Vong invasion.