Her is some info on your great coin, But sadly it is in rough condition, but I still want it :) This is a very cool Coin but the condition is not very low. It is Called a King George III silver Half Crown coin. struck in 1817 AD at the Tower Mint, London it is sterling (.925 Silver), the Engraver was - Thomas Wyon Weight / Diameter / Thickness 14.1 gm / 32 mm / 1.6 mm\
I hope all this info helps :) I wish you the very best of luck :)