The world's rarest diamonds available to buy

The Artemis and Apollo diamonds sold at auction with a final price of £44.9 million.

A pair of coloured diamonds are set to go under the hammer at Sotheby's Geneva in May 2017 which could break records for the most expensive earrings ever sold. The Apollo and Artemis diamonds, named for the brother and sister gods of power and beauty in Greek mythology, are currently set as a pair of earrings but will be sold separately due to their outstanding quality and value. The star of the two is Apollo, a 14.54 carat Fancy Vivid Blue diamond valued at $40 million, while its sibling is classed as a 16 carat Fancy Intense Pink diamond with a value of $14.5 million. Both are pear-cuts and, if sold to separate buyers, will likely be reset by their new owners.

The Pink Star diamond sold at auction at Sotheby's reaching $71.2 million.

The world's largest Internally Flawless Fancy Vivid pink diamond is set to go under the hammer at Sotheby's Hong Kong on April 4 and, with an estimate in excess of $60 million, may become the most expensive diamond ever sold at auction. The Pink Star was cut from a 132.5 carat rough diamond unearthed in Africa by De Beers in 1999 and took two years to cut and polish into a beautiful oval form which highlights the rare internal clarity and chemical purity of the stone. The Pink Star was previously offered for sale at Sotheby's Geneva in 2013, where it reached $83 million, but the buyer defaulted on the payment leaving the stone unsold and the title of most expensive diamond in the hands of the Oppenheimer Blue which went for $57.5 million at Christie's Geneva in 2016.

The Unique Pink diamond sold for $28 million at Sotheby's on May 17, 2016.

Weighing in at 15.38 carats, the Unique Pink is the largest Fancy Vivid pink pear-shaped diamond ever offered at auction. Recently cut and mounted as a ring by Cora International, the gem went on sale as part of Sotheby's Magnificent Jewels and Noble Jewels sale in Geneva on May 17, 2016.

Less than 5% of all diamonds are classified as true coloured diamonds and the Unique Pink is particularly special for its Type IIa certification - the most chemically pure class of diamond - from the Gemological Institute of America. As well as owning this incredibly rare stone, the new owner will also be able to rename it thus memorialising their purchase for posterity.

The Oppenheimer blue diamond has now been sold at auction reaching $57.5 million.

One of there rarest gems in the world, the Oppenheimer diamond became the largest Vivid Blue diamond ever to appear at auction when it went under the hammer at Christie's Magnificent Jewels sale in Geneva on May 18, 2016. Named for its previous owner and diamond connoisseur Sir Phillip Oppenheimer, this 14.62 carat rectangular-cut stone was accompanied by its original platinum mounting and a monograph from the Gemological Institute of America attesting its rarity, provenance and clarity.

The Oppenheimer blue diamond smashed its estimate of $38 - 45 million, eventually selling for $57.5 million, thus breaking records for the most expensive blue diamond ever sold.

The De Beers Millennium Jewel 4 has now been auctioned, reaching a sale price of $32 million.

This 10.10 carat, Internally Flawless, Fancy Vivid blue diamond is the largest oval blue diamond ever to appear for auction and is set be sold by Sotheby's Hong Kong on April 5, 2016. As the name suggests, it was part of the De Beers Millennium Jewels collection, comprising 10 rare blue diamond and one 203.4 carat white diamond (the Millennium Star - also in this list) which were displayed at the Millennium Dome and the subject of a consequent attempted jewellery heist.

The Millennium Jewel 4 is only the second diamond from the collection to be offered on the open market and, while it is unlikely to surpass the Blue Moon of Josephine which fetched $48.4 million in November 2015, estimates currently stand at a noteworthy $30-35 million.