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I was going through my collection and found this one that I had never noticed before. At first glance, I thought this might be some kind of error, but it's interesting how the pitting seems to follow what could be the edge of another coin's rim. Any ideas what might have caused this?

Hmm...wish I could tell you more. It is quite odd though.

Could have had another coin laying on top, the exposed part of the coin was subjected to environmental elements and the covered part was protected.