A Christie's member of staff displays a pear-shaped, D color, flawless diamond of 101.73 carats during an auction preview in Geneva, April 30, 2013. The successful buyer will have the privilege to give the gemstone a name as it is the first time this item is offered on sale. It is expected to sell around CHF 28,000,000 (US$ 30,000,000) when it goes into auction on May 15, 2013 in Geneva. [Photo/Agencies]

GENEVA - A pear-shaped colorless diamond weighing 101.73 was presented here in Geneva on Tuesday by Christie's and expected to achieve more than $20 million at an auction on May 15.

According to Jean-Marc Lunel, senior specialist at Jewellery Department of Christie's, this gemstone, one of the largest pear-shaped diamond known to date, combines perfect color-D and best clarity-Flawless.

"It is certainly an exceptional treasure, and most probably one of the perfect things that could be found on earth," Lunel told Xinhua.

The Gemological Institute of America estimated that there are no more than 600 diamond crystals that finish as polished stones between one and two carats with perfect color and flawless clarity, which means this is a grand event in the world of gems and jewellery.

The current auction record for a colorless diamond was set by the 76.02 carats cushion-shaped Archduke Joseph Diamond when it was sold for $21.5 million at Christie's Geneva last November.

76-Carat diamond set to be auctioned for over $15m