You got yourself the rarest mercury dime in the collection, only 250,000 were made and are rare and expensive.That one you got there i would class it as AU-50.but i looked at the back and it doesnt have double bars and you scrathced it so i would bump it down one grade to EF-40. So you have yourself a coin worth about 2,750 dollars. You are extremely lucky to have found that in a park.