Shipwrecked silver 8 reales cob coin recovered from the wreck of the Johanna (sunk in 1682)

This coin weighs 22.9 grams.

The Johanna, built in 1671, was an East Indiaman vessel for the British East India Company. In 1682, it wrecked near Cape Agulhas. Most of the treasure aboard was recovered in the 1980s, and according to the previous owner, this coin was among the thousands found on the wreck. 

The Spanish 8 reales or dollar enjoyed vast popularity throughout the entire world in the 17th and 18th centuries, being accepted as good money from Mexico all the way to China and the east. Up until as recently as 1858, they were legal tender in America, circulating alongside their native coinage for more than 60 years. Coins like this one were also among the very first coins to have been used in the Cape.

This example is a cob coin, which was manufactured in an unusual way. A bar of metal would be cast, then small pieces would be chopped off the ends and cut until they were at the desired weight. They would then be struck by a pair of dies, but as their shape was usually very irregular (this example being typical), only part of the design would be imparted onto the coin. This did not matter too much, as these coins were just considered weighed and marked bullion for the most part. Both gold and silver cobs exist.