The viewing of mining firm Rio Tinto's 2014 Argyle Pink Diamonds Tender collection began on August 12 in Sydney, Australia.

The auction - which will take place in October 8 - comprises 55 diamonds, four of which are hugely rare fancy red examples.

One in particular, a 1.2 carat piece called the Argyle Cardinal, is expected to make just over $1m.

The sale will include a number of hugely rare red diamonds

Josephine Johnson, manager of Argyle Pink Diamonds, told The Australian newspaper: "We have only produced 13 red diamonds from the Argyle mine in our 30-year history.

"The general rule of thumb in the industry is there are probably only 30 red diamonds in existence, so it makes this one a very rare, important diamond."

The world's largest red diamond sold for $2.1m at Christie's New York in 2012.

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