Thank you angelhart. I should have remembered to look at Nellie's panels on the Royal Jewels List board!! I am sure I need a brain transplant before my memory goes completely! Now I realise that it was on this board and the Royal Jewels List board where I saw the photos initially!
If anyone knows about Queen Mary's jewels, it is Nellie: our expert on HM's jewels.
For those who are unfamiliar with the board see http://royaljewelslists.boardhost.com/viewtopic.php?id=42 The jewel in question is shown in number 21 and 21a on the list in Nellie's panels which document Queen Mary's crown, tiaras and head ornaments.