The Roonstones were extremely valuable crystals found in the Umboo province on the planet Roon. As the maniacal Governor Koong deliberately destroyed the only known cache of roonstones, and the other set was thrown into the Roon Sea, it was presumed that the only surviving gems was the one on display in the Baobab Archives and the one Admiral Terrinald Screed gave to the Emperor.
The stone in the archives was retrieved by the intrepid explorer Mungo Baobab, who set off to find the stones with his droid companions, R2-D2 and C-3PO. This particular gem was encoded with the Dha Werda Verda, an epic poem of the conquest of the Zhell, indigenous people of Coruscant who may have been the ancestors of the Human race, by a warrior race called the Taungs, who later became the Mandalorians.
Kessum was a type of Roonstone.