Marked pt900, with a 0.15 stamp. The 0.15 stamp indicates a design with two diamonds, 0.1 and 0.05, connected. The larger 0.1 diamond (below) is about 3mm in size. Although very small, it's a design that dangles and sways, connected by a round clasp. I bought this intending to attach it to a necklace I already own, but I couldn't thread it through. Please be aware that the hole for threading is only about 3mm wide when purchasing. Material... Platinum Decoration... Diamond