Thetalian Prime is an inhabitable planet, the homeworld of the Retizian race. Corlandium is an extremely valuable mineral commodity there, being worth around a million times its weight in gold-pressed latinum.
The USS Saratoga visited the planet prior to its destruction. The away team, Benjamin Sisko, Aidan Thorn, Graal, Miriam Laffer and Hranok, were infected by organisms and contracted a disease. It threatened their lives until Doctor Laffer found a cure. (DS9 novel: Saratoga)