Thank you, Beth. I had not spotted this occasion of the Duchess of Cornwall wearing the large pearl necklace.
I think you are right about Queen Mary's necklace being different from Camilla's. Queen Mary's pearls are quite regular in size (I think she was the type of woman who was able to afford perfectly-matched pearls...), but I now feel like Camilla's pearls being slightly bigger than the ones worn by Queen Mary.