Made for a future Duchess of Devonshire with opals from Australia, the transformable jewel was worn at Elizabeth II's coronation and, this February, at a London film premiere.
A Cartier black opal and diamond tiara, made about 1937 for Mary Cavendish, then Marchioness of Hartington and later Duchess of Devonshire, is lot 1082 in Sotheby's Royal & Noble Jewels sale in Geneva on 11 November 2026. It converts into a necklace and five brooches, and Sotheby's estimate is CHF 780,000 to 1,100,000.
The jewel
The piece is offered by Sotheby's as lot 1082 in its Royal & Noble Jewels sale in Geneva on 11 November 2026, with provenance from Mary Cavendish, Duchess of Devonshire (1895 to 1988), and thence by descent. According to the lot page it is a tiara that takes apart into a necklace and five detachable brooches, each centred on an oval black opal and set with old mine, old European and single-cut diamonds, with baguette diamonds and a pear-shaped diamond at the front. A fitting lets the three central brooches be worn together as a corsage ornament. The fitted case is stamped Cartier, and Sotheby's dates it to about 1937.
Opals from a royal tour
Sotheby's says that, by family tradition, the client supplied the stones herself. Her husband, the Marquess of Hartington, was Under-Secretary of State for Dominion Affairs and the couple made a government tour of Australia and New Zealand in 1936 and 1937, during which they were given the opals. The auction house suggests the jewel was most likely commissioned around the coronation of George VI in 1937, a year that brought Cartier's London branch a wave of grand commissions. Lord Hartington succeeded as 10th Duke of Devonshire, of Chatsworth, in 1938.
Two coronations and a film premiere
By 1953 the Duchess was Dowager Duchess and Mistress of the Robes to Elizabeth II. At the coronation that June she walked behind the Queen and wore the opals as a necklace with the Devonshire diamond palmette tiara, Sotheby's notes, on the first British coronation to be filmed in full colour. She held the post until 1967. The jewel was shown in the V&A's Cartier exhibition in London in 2025, and on 5 February 2026 the director Emerald Fennell wore the necklace to the London premiere of her film of Wuthering Heights. The same sale also includes a sapphire demi-parure from Princess Birgitta of Sweden, which we will cover separately.
Why provenance and design lift a jewel like this
Black opal is the most prized type of opal, valued for its dark body colour and the play of colour across it, and Art Deco pieces by Cartier are among the most collected jewellery of the 20th century. Add a documented owner, a photographed public life and a design that can be worn several ways, and a jewel stands apart from one with an unknown history. The same factors apply on a smaller scale to family pieces: a maker's signature, an original fitted case, period photographs or letters all help. You can browse our opal jewellery and Art Deco jewellery, and if you have antique jewellery to sell, see how to sell your antique jewellery with us. Every piece is different: send us a few photos and we will tell you what yours is worth, free and with no obligation.
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- View the sale at Sotheby's: Royal & Noble Jewels, Geneva, 11 November 2026
- Lot 1082: Cartier Art Deco black opal and diamond tiara/necklace-brooch combination, at Sotheby's
- The Court Jeweller: The Devonshire opals to be sold (21 Oct 2026)
- The Court Jeweller: The electric opal and diamond tiara made for a Marchioness of Hartington (Oct 2025)
Facts as published by Sotheby's on its lot page, and by The Court Jeweller. Mozeris Fine Antiques is not connected with Sotheby's, Cartier or anyone named. No photograph is used because no image issued for editorial use was available.
