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 dubbed the “Argyle Violet.”

It is the largest violet diamond ever recovered from the mine. And now it will embark on a world tour, of sorts, as part of the 2016 Argyle Pink Diamonds Tender.

The Gemological Institute of America assigned the oval-shaped stone a color grade of fancy deep grayish blue violet. In a peer-reviewed article in the spring 2009 edition of Gems & Gemology, the GIA noted that the Argyle mine is the world’s only known source of type IaB hydrogen- and nitrogen-rich diamonds colored gray to blue to violet. The article also noted that the more violet-hued stones in this range are colored by nickel defects.

Rio Tinto said the Argyle Violet has a clarity of SI1.