RIO TINTO has unveiled a record four extremely rare red diamonds in an exclusive annual sale, with the company saying there was growing interest in the jewels as collectibles and alternative investments. The diamond tender, with stones sourced from Rio Tinto’s Argyle mine in Western Australia, will comprise 55 diamonds, including 51 pink and purplish reds and four fancy reds. The “hero” jewel at the centre of the sale – in its 30th year – is the Argyle Cardinal, a 1.21 carat radiant cut fancy red named after a northern American bird. The jewels routinely fetch $1 million (R11m) to $2m a carat. As a basic rule of thumb, pink and red diamonds are worth about 50 times more than white diamonds. – Sapa-AFP