Strange surface texture 1939d Germany 2 reichmarks km#93

Ppp

I posted this on the world coin forum and since more people are on the us forum I hope someone might have some input since this is more of a coin surface question. This coin is 62.5% silver.

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I just pick up a collection of German coins from wii. In the bunch there was a1939d 2 reichmarks with a strange surface texture (bumps and ridges) that I never seen before. I assume it’s some sort of pmd. Does anyone know what could cause this?
I included a picture of a normal 1939d 2 reichmark for comparison.
Thank you in advance for your comments.

1960NYGiants

Looks like it was in running water for a long time.