Trillium 323 is a highly prized mineral isotope possessed in large quanitities by the Caldonians. The Caldonians made access to this resource the center of their proposal to Premier Bhavani during negotiations for rights to the Barzan wormhole in 2366.
When the Caldonians withdrew from the proceedings, the Federation negotiator William T. Riker, attempted to secure their Trillium 323 in order to add it to the Federation's offer. However, before withdrawing the Caldonians had already come to an agreement with Devinoni Ral, representing the Chrysalians, over the Trillium 323. Ral subsequently added the mineral to the Chrysalian bid, greatly strengthening their offer. (TNG: "The Price")