It may have been exposed to elements (e.g., sand and wind) on one side for an extended period before being picked up. Also, during the coining process, the die may have been in a later die state. You see this often enough with coin Lincoln cents where a die from a die set is damaged badly and replaced. So instead of a LDS hammer die paired with an LDS anvil die, you might get something like EDS paired with LDS. Also, a capped die strike would be akin to this. As for its age...I just don't know.
Being mounted in jewelry or worn with one side rubbing and one side protected will do that. This has a clear mount mark at 12 o'clock.
I could think of one more thing. They used that medallion as a object of prayer. Someone revered the image of the person, a Pope maybe? They rubbed that one side during their prayer so much that it rubbed smooth. It probably was owned by a very devout Roman Catholic clergy or member.
If you don't mind, could you tell me where you got that medallion/medal? I know it represents the 1869 Ecumenical Council. Pius IX was Pope at that time but I couldn't find it on Google.
I think you nailed it. I think it was mounted on a necklace, and thumbed for a long time. The way it wears from bottom to top matches up, and if I rub it, it just feels right. gets more defined right where my thumb curls off the head. If that makes any sense.
I’m in the work die camp myself... who know what standards they have! Reminiscent of the 1922 us cent...
