Late Georgian era, foiled/closed back square emerald with rose cut diamond surround, set in silver over 12k gold, with a modern 18k gold bale.
Central emerald is 5.8mm and surrounding diamonds are approximately 2mm each. Component is 11mm by 9mm and 5.4mm thick and was converted to a pendant with a modern 18k gold bale. Weight is 2.9 grams.