Alexia's Jewel (Resident Evil Code: Veronica)

It's a Red Jewel that was attached to a choker.

Image of Alexia's Jewel
A small red jewel once part of Alexia's Choker.

This item is used in on the mural at the top of the central staircase in the Main Hall of the Antarctic Transport Terminal in conjunction with Alexander's Jewel and Alfred's Jewel to open the door.