This $2 million red diamond is the hero in Rio’s annual tender

[caption id="attachment_795066" align="aligncenter" width="600"] The 1.21-carat radiant cut “Argyle Cardinal" diamond expected to fetch over US$2 million. (Image provided)[/caption] A suitably named hero diamond, the “Argyle Cardinal,” is the main piece of Rio Tinto’s annual tender of ­Argyle’s rare coloured diamonds...