These earrings were made by Cartier for Dame Margaret Greville. They started off as drop earrings. Then in 1922, as the Art Deco era was in full swing, twelve diamonds were added, with another ten diamonds added in 1929.
The essence of Art Deco was geometrical shapes, and these earrings have the lot: trapeze cut, square cut, baggette and so on.
Dame Grenville left the earrings to the Queen Mother and they've been in the Royal Family ever since
Here is Elizabeth II wearing them