Thank you, MARG...!
Regarding the beautiful aquamarine and diamond earrings:
They were first seen during the Wales' tour through Germany in autumn 1987, in Munich. Their was never any info to be found about their provenance.
Speculation points towards the Gulf tour through four Middle Eastern monarchies exactly one year earlier - the Omani sapphires were first worn during the visit to Germany as well, and it's possible that the aquamarine earrings were also a gift from an Arab ruler given during the earlier tour.
The avatar picture of Diana wearing them was taken in late 1995, I believe... some evening function where Diana was accompanied by Al Fayed sr., wearing a rarely seen ice blue full-length C. Walker dress.