Solid xenon changes from face @-@ centered cubic ( fcc ) to hexagonal close packed ( hcp ) crystal phase under pressure and begins to turn metallic at about 140 GPa , with no noticeable volume change in the hcp phase . It is completely metallic at 155 GPa . When metallized , xenon looks sky blue because it absorbs red light and transmits other visible frequencies . Such behavior is unusual for a metal and is explained by the relatively small widths of the electron bands in metallic xenon .