Rio finds one of its largest white diamonds ever at Argyle mine

Rio Tinto's (ASX, LON: RIO) iconic Argyle mine in Western Australia has yielded one of the largest rare, gem-quality white diamonds in its 35-year history.

The 28.84-carat stone, named Argyle Octavia for its unusual octahedral shape, was found in March, the miner said.

The octahedral-shaped 28-carat stone is one of the largest ever produced by Rio Tinto's Argyle diamond mine, located in east Kimberley. (Image: Rio Tinto | Flickr.)

The find, said Argyle Diamonds' general manager Andrew Wilson, is unique in its size and shape, and it will take its place in the mine's history.

With the mine due to shut down next year, the Argyle Octavia could be the last major diamond it produces.

The gem, named Argyle Octavia, will be auctioned in Antwerp, Belgium, and could sell for millions. (Image: Rio Tinto | Flickr.)

In operation since 1983, the Argyle mine is renowned as the world's largest producer of coloured stones, particularly pink ones, with a much more sporadic presence of large white diamonds (0.00007% of its production in the last 36 years.)

Rio Tinto did not provide a price estimate for the diamond, which will be sold by tender at the world's diamond trade capital, Antwerp, later this year.