It's around 20mm in size and weighs 2.51 grams. I think there are some Fleur-de-lis on one side, although they appeared more obvious while out in the field. I can make out a date of 1643 and some letters are just visible.
The nearest coin that I've been able to find so far is a French 2 Dinar, although there aren't any dimensions mentioned. https://www.coinshome.net/en/coin_defin ... ducew2.htm
The coin in the link has the letter 'A' after the date, my coin appears to have the letter 'K'. I'm not sure if it is the same coin.

Any help appreciated.
