These are mini Aquamarine Pendants with metal rings. I have had people buy two to place on their loop earrings. It’s a great way to where this stones inexpensively at long last. 100% Brazilian. They are certainly selling well in the shops.
Team these with a cord for a casual look. Putting them with a silver chains looks lovely too and more elegant. The crystal size varies as these have not been precision-made. You may/may not get one of these in the photo. Note the dimensions are indicative. I will intuit the right one for your needs.