Actually, there's "nowhere near enough detail" for it to be genuine. It's supposed to be a Spanish-colonial 8 escudos, or "pirate doubloon", but the lions and castles that are supposed to be inside the quarters of the cross have degenrated into amorphous blobs.
This particular item is a mass-produced pewter replica, sold in bulk as "replica pirate coins"; you can buy them with antiqued copper, silver, or gold finishes. The shape and pattern of the cross-side is quite distinctive. We've seen multiple examples of them on the forum before, many from people who've dug one up on the beach, thinking they've found genuine pirate treasure when they've really found a relic of someone's Pirate Party treasure hunt.