Worn earlier this week for National Day (but hardly seen behind the hair) was one of several small colored stone tiaras from Luxembourg. This tiara features diamonds and five aquamarines, and it came from the collection of the late Grand Duchess Joséphine-Charlotte. It's part of a set which includes the bandeau-style tiara (which I believe can also be used as a bracelet), earrings, and a necklace with pendant, all made of large rectangular aquamarine stones joined by knotted diamond motifs.
Left to right: Joséphine-Charlotte, Margaretha, Maria Teresa. Joséphine-Charlotte wore it in bandeau style, closer to the forehead.
Like most of the tiaras belonging to the grand ducal family, this one has been seen on a few different family members: Joséphine-Charlotte and daughters Princess Margaretha and Princess Marie Astrid, plus daughter-in-law Grand Duchess Maria Teresa. I hope we see it on as many family members as they can manage, as it's grown to be one of my favorite aquamarine tiaras. Aquamarine just works so well in an Art Deco design, for whatever reason, and the diamond ornamentation here is subtle enough to allow the blue to take center stage. As we've seen in other tiaras, rectangular aquamarine stones aren't always the easiest to incorporate into tiara form (looking at you, Brazilian Aquamarine Tiara), but this one's a great example.