Apologies for the late reply. The last few days have been hectic.

I agree with Isabelle D here -- that it is the Cartier tiara. Initially I didn't think so, and wondered what jewel it was. I think that, as I found the image in a newspaper, there has been some retouching of the original photo which gives a different impression. So often the newspapers did that if they wanted something to standout. I posted the photo because I thought it was a charming one of the Queen -- and it was one I hadn't seen before. (And I wanted to try to get away from the usual English topics I pursue. People must get bored with me!)