This is a full moon ring. The lunar cycle affects our tides. A full moon means Spring tides, where the sea levels are at their most extreme. A super low-tide gives us a greater beach area to search, revealing areas that have been covered by the sea for weeks. Almost perfectly circular, this piece of glass may have been the top of a perfume bottle stopper. It could also have been a piece snapped from a vase, or jar and gently tumbled into this shape. A beauty.
2cm diameter x 0.5cm depth