A multi-gem necklace, including the Tsar Alexander III amethyst, by Prince Dimitri.

A diamond, peridot, tourmaline, garnet, heliodor, aquamarine, cultured pearl and multi-gem necklace, including the Tsar Alexander III amethyst, by Prince Dimitri. Photo: Christie's Images Ltd 2010

The front suspending the cushion-cut Tsar Alexander III amethyst, weighing approximately 42.44 carats, within a circular-cut diamond surround, set at the four corners and cardinal points with old European-cut diamonds and cabochon moonstones, from a sculpted 22k gold Knot of Savoy link, to the graduated series of oval-cut peridot, tourmaline, garnet, heliodor and aquamarine pendants, each within a circular-cut diamond surround, decorated with variously-cut rubies, emeralds, spinels, sapphires, garnets and moonstones, spaced by drop-shaped gray cultured pearls and two marquise-cut aquamarines, each from an old European-cut diamond, to the woven brown leather cord and sculpted 22k gold Knot of Savoy clasp, mounted in 22k gold and platinum, 18½ ins., in a Prince Dimitri pink velvet case. With maker's mark for Prince Dimitri, no. A802 - Estimate $200,000 - $300,000

Accompanied by two documents from Prince Dimitri, attesting to the provenance of the Tsar Alexander III amethyst

Notes: The Tsar Alexander III amethyst, weighing approximately 42.44 carats, is a recut and polished Siberian amethyst from the imperial Russian mines. It was given by Tsar Alexander III, along with a large collection of amethysts, to Prince Dimitri's great-grandmother, Queen Elena of Italy. Because of this connection to the Italian royal family, the House of Savoy, the necklace incorporates the Knot of Savoy, which is a symbol of eternal love.

Christie's, New York Jewels, 15 June 2010, New York, Rockefeller Plaza www.christies.com