Re Queen Mary. I don't think it is the lozenge tiara with the pearl surmounts.
Queen Mary is wearing her long diamond sautoir which Roberts wrote about. I suspect that, as a corsage brooch, Queen Mary is wearing the central part of the upper section of the diamond and pearl stomacher (with an additional drop pearl placed in the centre) which originally belonged to the Duchess of Gloucester who left it to the Duchess of Teck.
--Previous Message-- : I think these photos rule out these 2... the : shape is not there...? :