The Skull was incredibly magnetic, even attracting metals that weren't magnetic by nature, like gold. The Skull also had psychic properties, being able to communicate on a primitive level with other creatures by staring into the eyes for prolonged periods. These powers also affected non-humans such as siafu, where Oxley used the skull to divert and deflect their attack on himself and Jones.
Behind the scenes
It serves as the title McGuffin at the heart of Indiana Jones and the Kingdom of the Crystal Skull. The skull was a practical prop created by Stan Winston studios, with some versions outfitted to physically "glow" from the eyes. The crystal skull that is carried around throughout the movie is actually of a different size than that attached to the head of the crystal skeleton at the end of the film. Director Steven Spielberg claimed nobody would notice.