Tricellite was a durable, long-lasting mineral used as a substitute for zelebium in the inertial guidance systems of Class 9 cargo vessels. Some star systems, for instance Omega Sagitta, lacked this mineral. In 2365, the guidance system aboard the cargo ship Erstwhile, commanded by Captain Thadiun Okona, was repaired with tricellite. (TNG: "The Outrageous Okona" ) Tri-, three, cell-, chamber, and -ite, mineral; combine, three chambered mineral.