One of the world's largest flawless diamonds is attracting the interest of investors and jewellers alike as the rock worth between $20 and $30 million is set to go under Christie’s hammer on May 15.

The pear-shaped gem weighs 101.73 carats and it is considered perfect because of its color, which is rated "D," and its flawless clarity. It's also completely symmetrical and has a rare brilliance, Christie's says.

The diamond comes from a 236-carat rough that was found at the De Beers–owned Jwaneng mine in Botswana. It took 21 months to polish and it is expected break the auction record set by the $21.5 million purchase of the 76-carat Archduke Joseph Diamond last year.

According to industry publication JCK Magazine this rock “looks like one for the books," adding the gem is a "Type IIa," category that fewer than 2% of the diamonds in the world fall into.

The world’s most famous pear-shaped diamond is the Cullinan I, a colourless, Type IIA stone of 530.20 carats, which forms part of the British Crown Jewels.