Farnese Blue Diamond Sells for $6.7 Million One of the most famous diamonds in Europe was sold in Geneva on Tuesday. The “Farnese Blue” is a blue diamond, one of the rarest gems in the world, and is 6.16 carats. It gets its name from Elizabeth Farnese, the second wife of King Philip V of Spain, who got it as a wedding gift in 1715. The diamond traveled all over the world leading up to the sale at Sotheby’s Geneva on Tuesday, stopping in New York, London, Singapore and more. The $6.7 million price tag exceeded the pre-sale estimates by almost $2 million.