Unfortunately, it's a modern reproduction. Crude trinkets such as these are sold widely in gift shops and are often crude compositions that hardly resemble the actual coins.
It looks like a fake. The side with the cross, looks like an early (before 1652) 8 reales Spanish colonial cob coin, from the Potosi/Bolivia mint. The other side looks fake, as far as I know, although I'm not an expert. I've looked at a lot of cob coins, and I've never seen a cob, with "Eight Reales Silver Cob" written in English. An early Potosi cob should have a cross on one side, and a shield on the other side.
The best place I know, to buy an authentic cob coin, is at a Sedwick auction. As far as I know, they have the best reputation, for ensuring that their cob coins are authentic, among all sellers of cob coins. I bought a cob from them, last year. They have only 2 auctions per year, and you can bid online. Their next auction is on May 7 through May 10. They also have a store, but in my opinion, the best coins, at the best prices, are in their auctions. Here is a link, to their next auction. You have to register in advance, to be eligible to bid. They sell gold cobs, silver cobs, milled coins, artifacts, and some ancient coins. Some of the coins, are known to have been salvaged from shipwrecks, at the bottom of the sea. Those coins, if silver, are usually more corroded, but some look pretty good, depending on where the coins were, within the pile of coins. The shipwreck coins usually sell for a premium. For a small fee, they will also provide their certificate of authenticity (COA), which has photos of the coin on the certificate, if you win the coin at their auction. Some coins already have a COA. https://auction.sedwickcoins.com/auctionlist.aspx A very good, relatively inexpensive book, about cobs, is "The Practical Book Of Cobs Fourth Edition", written by Daniel Sedwick and Frank Sedwick. It costs $60 on Amazon, but it costs only $20 on Sedwick's web site, at the moment, I think. A good book, about Potosi 8 reales cobs in particular, is "8 Reales Cobs Of Potosi" by Paoletti. It costs $45 plus shipping on Sedwick's web site, at the moment, I think. https://www.sedwickcoins.com/books.htm Here are my photos, of the cob, which I won last year, at a Sedwick auction. It is a silver Potosi 8 reales cob ("Piece Of Eight"), from the reign of Philip II of Spain, assayer RL, minted in the 1590s in the new world. Weight = 27.20 grams. Width = 37.7 mm. Height = 37.1 mm. It is not a shipwreck coin, as far as I know. Perhaps no one knows.
