These three brooches have in common one of the best known features of Art Deco: the introduction of semiprecious stones in fine platinum and diamond jewellery. It was actually Cartier in the early 1910's who first used the combination with onix and he did it in a panther watch. Diamonds and platinum on black were popular before but cloth, like the Belle Époque velvet chokers. These three pieces are signed by Cartier and were made in that period. They will be auctioned by Christie's in NY on April 12th.
This one is enamel, not onix, but as stunning as the others, probably black enamel was used to adapt it better to the shape.