A Rare 'Chameleon' Diamond and Diamond Ring. Photo courtesy Tiancheng International

Centring on an emerald - cut "chameleon" diamond weighing 6.13 carats, flanked on each side by a shield - cut diamond, mounted in platinum. Ring size 6. Estimate HK$2,000,000 - 2,800,000 US$256,400 - 359,000

Accompanied by GIA report *12864602 dated 04 May 2011 stating that the 6.13 carats diamond is natural, Fancy Deep Brownish Greenish Yellow colour, SI1 clarity, also comments that the colour of this stone changes temporarily when gently heated, or when left in darkness for a period of time and is known in the trade as "chameleon".
In Gem and Gemology spring 2005, chameleon are stated as the rarest among gem diamonds. The rarity of chameleon diamonds and their interest for the connoisseurs are due to their unusual ability to change colour temporarily when heated to about 150oC.

Tiancheng International. Hong Kong Autumn Auction 2011. 28 Nov 2011 www.tianchengauction.com