A 6.46 carats Type IIa diamond ring, by Van Cleef & Arpels (Estimate $350,000 – $450,000) and A 20.97 carats Burma sapphire and diamond ring Estimate $150,000 – $200,000. Photo Christie's Image Ltd 2015

A 6.46 carats Type IIa diamond ring, by Van Cleef & Arpels. Estimate $350,000 – $450,000. Photo Christie's Image Ltd 2015

Set with an oval brilliant-cut diamond, weighing approximately 6.46 carats, flanked on either side by a pear-shaped diamond, ring size 6 1/2, mounted in platinum. Signed Van Cleef & Arpels, no. M 41139

Accompanied by report no. 17438638 dated 12 August 2015 from the GIA Gemological Institute of America stating that the diamond is D color, Internally Flawless clarity

With a supplemental letter from the Gemological Institute of America stating that the diamond has been determined to be a Type IIa diamond. Type IIa diamonds are the most chemically pure type of diamond and often have exceptional optical transparency. Type IIa diamonds were first identified as originating from India (particularly from the Golconda region) but have since been recovered in all major diamond-producing regions of the world. Among famous gem diamonds, the 530.20 carat Cullinan I and the 105.60 carat Koh-i-noor, are examples of Type IIa

A 20.97 carats Burma sapphire and diamond ring. Estimate $150,000 – $200,000. Photo Christie's Image Ltd 2015

Set with a cushion-cut sapphire, weighing approximately 20.97 carats, to the circular-cut diamond surround and half hoop, ring size 6, mounted in platinum

Accompanied by report no. 11060146 dated 21 June 2011 from the Gübelin GemLab stating that it is the opinion of the Laboratory that the origin of this sapphire would be classified as Burma (Myanmar), with no indications of heating

Christie's. IMPORTANT JEWELS, 20 October 2015, New York, Rockefeller Plaza