Sydney: Global mining giant Rio Tinto's largest and most exquisite diamond, Argyle Violet, is expected to fetch a multi-million dollar bid when showcased as the dazzling centrepiece of Rio's auction later this year, it said on Tuesday. The violet coloured diamond unearthed from Rio's Western Australia diamond mine is 2.83 carat polished oval shaped diamond, and will be showcased in Rio's 2016 Argyle Diamonds Pink Tender, Xinhua news agency reported. More than 90 percent of the world's rare pink diamonds come from Rio's Argyle mine in the Kimberly region of Western Australia state. The mine is the only known source of the exceptional violet diamonds, producing only 12 carats of polished gems for the tender in its 32 years of operation. "Impossibly rare and limited by nature, the Argyle Violet will be highly sought after for its beauty, size and provenance," Rio Tinto Diamonds general manager of sales Patrick Coppens said. The tender attracts private bids for Rio's most exclusive diamonds with prices fetching over one million Australian dollars per carat. The 2016 Argyle Pink Diamonds Tender will commence private trade viewings in June and travel to Copenhagen, Hong Kong and New York.