Coyote Diamond is the world's largest diamond, known for its flawless surfaces and clarity.
Fox sent Jackal and Hyena to steal the Coyote Diamond from the Diamond Exchange in 1994. However, Xanatos bought it before they could steal it, saying it would go nicely with the Star of Arabia. Xanatos' purchase of the Coyote Diamond prompted Jackal and Hyena to attempt to steal it from him and led to their attempted assassination of him at Xanadu. (In fact, Fox really sent Jackal and Hyena after the Coyote Diamond as part of Xanatos's scheme to recruit Derek Maza to his cause). ("Her Brother's Keeper")
Two years later, Xanatos incorporated the diamond into the body of Coyote 5.0. ("The Rock") This was to speed up Coyote 5.0's light-based mental processes, making its A.I. more enhanced than previous models.  Coldsteel returned it to Xanatos after Coyote 5.0 was demolished by Coldstone. ("Rock of Ages")