$1 million tag on Vulcain diamond

Vulcain: The pear-shaped stone is the world's largest single diamond

PARIS, France -- The world's largest perfect diamond, which took 15 years to design, is expected to fetch more than $1 million when it goes to auction.

The single-crystal diamond, named the "Vulcain," is a 179-carat black, pear-shaped gem and has an interior of amber-coloured crystallised graphite formations.

It took experts 15 years to chip and polish at the diamond, filing it down to half its original 380 carats to show off its features, auctioneer Charles Peiffert told Reuters news agency.

The Vulcain will go under the hammer in Saint-Amand-Montrond in central France on June 27.

"Its faceted pear-shaped form, its shine and its internal structure make it a unique and exceptional stone," said Peiffert.

"We had to hunt all over the world to find a craftsman skilled enough to whittle it down.

"Single-crystal diamonds are much rarer and its formations make this one particularly special."

Although it is the largest single diamond to go on sale, it is beaten in size by a $1.7 million 498-carat multi-crystal diamond.