Looking on Getty images I found this close-up photo of the orange stone brooch worn to Ascot 2007 that I don't remember seeing this detailed view previously. This is my favourite brooch Camilla has worn, so it's a shame she hasn't worn it more than once! Beth found that the brooch is a match for one owned by the Queen Mother, link to Beth's post:
https://mb.boardhost.com/historyroyaljewels/msg/1632728803.html