The coin might have been a very nice example of the type.
Not anymore !
The thrill of finding something like this makes it difficult to keep from doing something regrettable.
And something regrettable was done. Proper cleaning generally takes time and harsh methods can lead to less than satisfactory results. The coin in this state is worth a few euros. It may have brought 20 if not for having been stripped to the bone.
If you find anymore please ask for advice from more than one person. Preferably someone who has experience with these types of things. People here will be happy to help out.