Melbourne, Australia–Last year, Rio Tinto made an astounding discovery at its Argyle mine in Western Australia and never said a word about it. The diamond mining company unearthed a 9.17-carat piece of rough that yielded a stone Rio Tinto Diamonds’ Patrick Coppens describes as “impossibly rare”–a 2.83-carat fancy deep grayish blue violet diamond that it

Melbourne, Australia–Last year, Rio Tinto made an astounding discovery at its Argyle mine in Western Australia and never said a word about it. The diamond mining company unearthed a 9.17-carat piece of rough that yielded a stone Rio Tinto Diamonds’ Patrick Coppens describes as “impossibly rare”–a 2.83-carat fancy deep grayish blue violet diamond that it