Courtesy of Gallica, the digital library of the Bibliothèque Nationale de France, I discovered this extraordinary diamond parure, by Cartier, which was displayed in a charity exhibition to the benefit of people affected by the war, at the Petit Palais in Paris, in 1917:



The picture was published by the monthly magazine Les Modes (1917, N°172, p. 11, via gallica.bnf.fr)

The caption says the jewels were valued at 1 million francs.