Rio Tinto (LON:RIO) unveiled Tuesday a rare 2.83-carat violet diamond, the largest of its kind ever found at Australia's remote Argyle mine, which could sell for more than $4 million.

The oval shaped rock, known as the Argyle Violet, will be the centrepiece of the 2016 Argyle Pink diamonds tender, the annual showcase of rarest diamonds unearthed from the mine.

The Argyle Violet, found in August last year, originally weighed 9.17 carats and had etchings, pits and crevices. The company says it took more than 80 hours of work to polish it down to what is now.

While the company did put a figure on the diamond’s worth, it is estimated the gem could attract offers anywhere from $1m to $2m a carat.

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