LONDON, Feb 19, 2008 (AFP) - The biggest colourless diamond to appear at auction for 20 years will go under the hammer later this year, officials said as it was unveiled in London Tuesday, January 19th.

The biggest colourless diamond - Photo : Leon Neal/AFP

The 101.27-carat stone, which will be sold at the Hong Kong branch of Christie's auction house on May 28, is expected to fetch in excess of six million dollars (three million pounds, four million euros).

"Only three colourless diamonds of over 100 carats have ever appeared at auction, all sold in Geneva," said Francois Curiel, chairman of jewellery at Christie's.

"With Asia becoming such a vibrant market, it is fitting that this rarest gem should be offered ... to the growing number of collectors in this region," he added.

The diamond was found at the Premier diamond mine in South Africa, and is being sold by a Europe-based diamond trading company.

In 1990 the Mouawad Splendor, a 101.84-carat pear-shaped diamond, sold for 12.7 million dollars.

The diamond unveiled Tuesday will be on view to the public in London from Saturday until February 27.