This brooch has so much history and with the engraving on the back we are able to date it to Circa 1819. Probably worn to mourn Henry Birdridge (The name engraved on back) who died at the age of 59 on 2nd Feb 1819.
Measuring 27mm x 25mm, slightly arched, the open face locket section measuring 16mm x 13mm and is surrounded by 12 round garnets. The back also has an open locket section. Hinge pin and 'C' catch. Gross weight 6.4g. No hallmark but tests as 9ct.