Trisilicate was a valuable mineral ore found in high quantities on Peladon. Much of the technology of the Galactic Federation is based on it.
When the Federation went to war with Galaxy 5, the use and control of the trisilicate supply became vital to their war effort. The mining and refinement of the ore was threatened by a workers' rebellion against the rulers of Peladon and the Federation. The traitor Eckersley, with the help of renegade Ice Warriors, also planned to ship the ore to Galaxy 5, but they were thwarted by the Doctor. (DW: The Monster of Peladon)
By 3985 the trisilicate mines were almost totally mined out. (NA: Legacy)