It is not, sadly, a genuine coin. It's definitely not in the style of a coin from the 1700s. The design is loosely based on the 6 kreuzer coin of Bavaria, dated 1766, in the name of Elector Maximilian III Joseph. KM# 247, see this example on ma-shops for an example of what it's supposed to look like.
I can't tell if this coin is completely fake, or simply heavily worn and had its design carelessly tooled back on. The genuine coins are base silver (.333 fine) so the yellowish colour isn't a reliable guide. If it's a genuine but tooled coin, the coat of arms has been partially replaced with an inscription of some kind; perhaps it's a love token. If it's a completely fake coin, it appears to have been turned into a button at one point; perhaps its a jewellery copy of that coin, made to be turned into a cufflink and only intended to resemble a coin at first glance.
Either way, I don't think it's worth much.