I think it could be the diamond hoop earrings, as suggested by TheRoyalsAndI, or the Vasa earrings, worn without their central diamond briolette drop:
(Picture: Norsk Telegrambyra AS / Reuters / Lise Aserud / NTB Scanpix)
Queen Silvia also wears the large floral brooch which is part of Empress Amalia of Leuchtenberg's Brazilian parure. Queen Sonja wears the corsage brooch of Queen Maud's wedding gift pearl and diamond parure. And Queen Margrethe II wears her Russian sapphires.