Hi Wooster,
What a magnificent find! it looks very very old, and yes looks like a hammered coin (ie before coining presses came into being circa 1790's in Birmingham, England) looks like a Tuetonic Eagle, I think it looks too old to be an Imperial Prussian Medallion.
Did you find it on a Goldfield? me'thinks that some European digger had lost his family hierloom / goodluck charm - I'm sure that he would have been quite distraught! - congratulations it is a great find.
CASPER