The most valuable diamond to be offered at auction is expected to fetch in excess of £37 million (A$72.13 million).

Sotheby's was giving previews of what it calls the world's most valuable diamond ever to be offered at auction.

Sotheby's said in a statement that The Pink Star, a 59.60-carat oval cut pink diamond, would go up for auction on November 13 in the historic five-star Beau-Rivage Hotel along Lake Geneva.

David Bennett, chairman of Sotheby's Switzerland, says the vivid pink diamond is "of immense importance" because of its extraordinary size and exceptionally rich color that surpass all others known to exist in government, royal or private collections.

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He says it is "simply off any scale, and passes, I believe, into the ranks of the earth's greatest natural treasures."

- AP