On looking at it more closely, you can see a collection of tiny linkages at the bottom of the divot in the middle, as if it is actually designed to have a mechanical contraption plug into it, rather than a gem. You can also see that it has a pair of tiny power leads coming out the back.
Characters In Game: Moloch
All Characters: Moloch
The following were notes made while this was in development. They do not necessarily represent the final state of the thing.
A small brooch, which is clearly part of a mechanism. It has a divot in the center, with some exposed gears that look like they are supposed to hook to something. And it has some connections at the bottom that look sort of like power leads.