Moonstone

A Moonstone was a stone disc of Atlantean technology featuring four lunar symbols: waxing moon, full moon, waning moon, and new moon. It was used as part of combination mechanism for accessing the Greater Colony and the entrance of Atlantis.

Behind the Scenes
The Moonstone appears in the video game Indiana Jones and the Fate of Atlantis and the place it is found differs between the plot branches.
 * In the "Team" and "Fists" path, a moonstone is found in the ruins of Knossiss.
 * In the "Wits" path, Indy must steal the moonstone while aboard a Nazi submarine.