Two flawless white diamonds, each weighing over 50 carats, and a dark grey-blue gem, known as The Farnese Blue, were on display at Sotheby's auction house in London on Friday. All three gemstones will be auctioned in Geneva on May 15. The white diamonds — both discovered in Botswana — are expected to fetch more than $15 million (€12.2 million) at auction. According to Deputy Chairman of... Еще Jewellery Europe at Sotheby’s Daniela Mascetti, “they are absolutely the best, the clearest of all stones and beautifully cut. They are quite extraordinary, quite extraordinary to have two such stones in the same sale.» The Farnese Blue, a 6.16 carat blue diamond gifted to the Queen of Spain, Elisabeth Farnese, in 1715, could sell for anywhere between $3.7 and $5.3 million (€3 and €4.3 million). According to Sotheby’s, it «emerges onto the market for the first time, after having passed down through four of Europe's most important royal families.» It is thought to be one of the most important historical diamonds left in private hands.