IT'S the size and shape of a 10 cent piece but the bidder who wants to take home the largest diamond ever auctioned in Australia will have to find notes, and plenty of them, to meet the price tag.
The huge rock, which weighs 9.79 carats and is of extremely high clarity, was flown into Western Australia today under tight security.
The round, brilliant cut solitaire is due to go under the hammer in Perth on Sunday, with the sale sparking interest in the sparkler across the Asia-Pacific region.
But First State Auctions, which is auctioning the stone, is reluctant to guess what price it might reach, saying only that a similar quality stone weighing five carats sold in Perth for $60,000 earlier this year.
Part of the Sydney estate of a South African diamond miner, the diamond has been assessed as VVS, a measurement of clarity ranked just below flawless, which the auctioneering company today said was remarkable considering the size of the gem.
Company manager Lara Taibel said there was a sense of anticipation leading up to the sale, set to take place at the Parmelia Hilton hotel.
"A diamond of this size generates real excitement and we feel privileged to be auctioning a stone of this calibre. It is the most expensive piece ever auctioned by First State Auctions," Ms Taibel said.
"To put the size of the diamond into perspective, your average engagement ring is generally created with a 0.5 carat diamond of a lower quality than this stone, so we're expecting to have a few people swooning at the display case."
The diamond's quality has been independently assessed, and certification from Australian gemologist Bill Sechos will be provided to interested bidders.
A diamond of similar size makes up the centrepiece of the antique 1920s engagement ring that American film actor Michael Douglas presented to Welsh actress Catherine Zeta Jones.
The value of that ring was estimated in 2000 to be Stg2 million ($A5.22 million).