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Mining giant Rio Tinto said it has unearthed a "remarkable" 12.76 carat pink diamond in Australia, the largest of the rare and precious stones ever found in the resources-rich nation.

Named the Argyle Pink Jubilee, the huge rough stone was found at Rio's pink diamond operations in the Kimberley region of western Australia and would take 10 days to cut and polish, the miner said on Wednesday.

"This rare diamond is generating incredible excitement. A diamond of this calibre is unprecedented -- it has taken 26 years of Argyle production to unearth this stone and we may never see one like this again," said Josephine Johnson from Rio's Argyle Pink Diamonds division.

"The individual who gets to wear this remarkable pink diamond will be incredibly lucky indeed."

The light pink Argyle Jubilee is a similar colour to the 24-carat Williamson Pink given to Britain's Queen Elizabeth II as a wedding gift which was later set into a Cartier brooch for her coronation.

The Williamson was discovered in Tanzania in 1947 and is ranked among the finest pink diamonds in existence.

Rio produces more than 90 per cent of the world's pink diamonds from the Argyle mine, and said large stones like the Jubilee typically went to museums, were gifted to royalty or end up at prestigious auction houses like Christie's.

Christie's had only auctioned 18 polished pink diamonds larger than 10 carats in its 244-year history, Rio said.

When the Jubilee diamond has been cut and polished it will be graded by international experts and showcased globally before being sold by invitation-only tender later this year.