Marcasites, as used in jewellery, are made of pyrite (fool’s gold) and has been made since the time of the Ancient Greeks. It was particularly popular in the eighteenth century, the Victorian era, with Art Nouveau jewellery designers and now with costume jewellery, silver jewellery and watches.
They are a small, inexpensive and very popular stone typically glued in when setting. They commonly fall out with wear over time. oagems.com carry a full calibrated range of round swarovski marcasites and so that you can quickly and easily replace any missing marcasites from jewellery and watches.