There are tiaras, and then there are tiaras like the Londonderry Diamond Tiara. This piece dates to the middle of the nineteenth century; it was a part of a diamond parure made for the family in 1854 by Garrard, although the tiara itself was not originally an all-diamond piece. The center of each element was originally designed to hold a pearl, and the tiara could also be worn topped by tall pear-shaped pearls, increasing the height of the piece substantially.
Today, the diamonds at the center of each element are mounted en tremblant. The piece is almost a complete circlet, encircling nearly the entire head of the wearer. (The tiara is magnificent, but it’s not the only one the Londonderrys own — they’ve also got a famous set of amethysts, given to them by Alexander I of Russia, and a pearl necklace that can be worn as a tiara.)