Rio Tinto biggest pink diamond ever is expected to sell for at least $10m.

The 12.76 carat gem to be known as the Argyle Pink Jubilee is being cut and polished in a painstaking 10-day process.

It was found at Rio Tinto's Argyle mine in the remote east Kimberley region of Western Australia, which produces more than 90 per cent of the world's supply of pink diamonds.

The gem is being cut and polished as a single stone by Richard How Kim Kam, who has worked for the company for 25 years.

"I'm going to take it very carefully," Mr How Kim Kam said.

"I know the world will be watching."

Rio Tinto said pink diamonds attracted, on average, 20 times the price of an equivalent white diamond.

The finished gem will be graded by a team of international experts and shown around the world, then sold under a tender process later this year.

Argyle Pink Diamonds manager Josephine Johnson said a diamond of its calibre was unprecedented.

"It has taken 26 years of Argyle production to unearth this stone and we may never see one like this again," Ms Johnson said.