The biggest pink diamond ever sold is set to be auctioned next month - and is expected to fetch over $8 million (£4.9 million).  

According to auction house Christie's, the Martian Pink, a 12.04-carat pink diamond, is the largest ever to hit the auction market.

The gem is staggeringly rare, and is one of only two pink diamonds in the world which are said to be of 'significant size'. The other is the 23.60-carat Williamson Pink diamond, which was presented to Queen Elizabeth II as a wedding gift.

While most natural pink diamonds have a tinge of purple, grey or orange to them, this stone shows no trace of a secondary colour.

It is presently owned by a private collector, and was given its name by American jeweller Ronald Winston in 1976, the year America launched its first satellite mission to Mars.

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