That's what I was wondering but it's the same size as a dime and has the ridges like a dime. But yeah I have no clue
Possibly shrunken via high voltage... I'm guessing the ridges you mention on the edge don't look even and nice like a dime.
May have been sitting inside a coil of sorts and blasted with thousands of volts... probably on purpose. I'm guessing what you're seeing there is the actual pattern from high voltage and some melting as well... There are YouTube videos of people shrinking coins with electricity...
Do the 'ridges' resemble small file marks maybe? I had a friend in high school shop class that altered a nickel to make a charm necklace. He cut away most everything around Jefferson's head. With a hobby saw that had a reciprocating filing attachment, he struck the edge circumference and produced small vertical cuts like reeds on it. The charm eventually looked like this:
OP said it was the size of a dime...so that wouldn't shrink it...If you entirely remove the rim of a penny is it the same size as a dime? Maybe I'm thinking too hard lol! but may have gotten some acid on it after electrocuting it...because why the heck not lol!!! Or again...too much thinking at my bed time lol!
PMD, or as @paddyman98 would say, "DEFDAM". The what happened and why will remain a mystery unless you know the person that did it.
This looks as if the coin was sitting flat on the reverse and then the Obverse was shot peened. the surface and edge are covered in round looking divots, as if the coin was intentionally played with. Not a mint produced surface.