An unassuming crystal sculpture possessing immense teleportation powers. The crystal skull is believed to be designed by the giant aliens of P7X-377. In concert with lepton radiation the crystal skull teleports anyone who looks into its "eyes" to another location.
Two crystal skulls of identical design have been located. One was discovered by Dr. Nicholas Ballard in 1971 during an archaeological excursion to Belize. He discovered a hidden chamber within an ancient temple where he was teleported to P7X-377 to see the giant aliens. After not responding to their words, they sent him back, and Nick left the chamber, the skull in tow, before it collapsed.
A skull of equal design sits on a pedestal in the midst of a vast pyramid where the giant aliens reside on 377. Similar in the way the Stargate works, one skull is able to "signal" its counterpart and transmit a person in his or her entirety to the location of the other skull.
Without the radiation, teleportation cannot be achieved and the skull has no more use than a paperweight. If, however, teleportation commences and is interrupted by an energy-based weapon like a zat'ni'katel, the process is stalled and renders the individual invisible, trapped between two continuums until he or she can complete the process by looking into the eyes of the skull again.
Crystal Skull - SG-1 enters a pyramid on P7X-377 and discovers a crystal skull which was identical to one Nicholas Ballard located in Belize.