That coin looks very similar to the coins my buddy finds at the beach near us. They sit in that salt water for so long they develop a crust that you have to break off or use electrolysis on them. The coin inside still has most of it's details but it becomes very thin and smaller in diameter.
http://www.treasurenet.com/f/index....20859.0.html
http://www.treasurenet.com/f/index....20859.0.html



















