“Crystal Skull” is episode twenty-one of season three of Stargate SG-1.
SGC discovers a Mayan pyramid that, along with a neutrino slowing material, holds a crystal skull. Only, it’s not where you would normally expect to find a Mayan pyramid.
Daniel’s grandfather had found an identical one in Belize. One which supposedly transported people to see aliens, when the eye sockets were gazed into. Getting the skull is risky, as the chamber it is in could be quickly hazardous to humans.
When Daniel gazes into the skull, he vanishes – at least from the eyes of the rest of SG-1. He seems to be out of phase to everyone else, and most material objects.
The skull is similar to the legendary Mitchell-Hedges crystal skull, although pink, which is carved from a single piece of crystal, although that one has been proven to be a fake.