I would concur that it is a Silver Slipper coin center inserted into a Palace Station $1 plastic outer part.
Here's picture of the Palace Station chip --

I've seen others done this way also. Not a factory error, but can be done by popping out the coin center and switching it onto another chip. If you know how to do it, and if done carefully, there's no telltale marks ... unless under magnification, perhaps. I think the colloquial term for this type of chip is a "mule".