Kejelious was a substance, a type of clay used by the ancient Bajoran people in the Sh'dama Age for making pottery.
In 2376, Jake Sisko uncovered a shard of kejelious in B'hala, much to the delight of Eivos Calan, who was eager to talk about the properties of the versatile material. (DS9 - Avatar novel: Avatar, Book One)
In 2376, Jake and Opaka found Kejelious fragments on Idran IV. (DS9 novel: Rising Son)