Crystal skull

Crystal skulls were devices, built by the Giant Aliens, with a function of transportation and Dimension Shifting with the use of Leptons.

A Crystal skull, identical to the one Daniel's grandfather Nicholas Ballard discovered in 1971 in Belize, was discovered in a Mayan ziggurat by SG-1 in the year 2000. Daniel then briefed SG-1, General Hammond and Doctor Fraiser on the skull that his grandfather found, explaining that his grandfather believed the skull transported him to another planet where he met aliens.