LONDON, April 6 (Reuters) - The historically important Farnese Blue diamond, which was passed down through European royal families for some 300 years, is to go on sale for the first time next month, auctioneers Sotheby's said.
Expected to fetch between $3.7 and 5.3 million, the 6.1 carat, dark grey-blue stone from the Golconda diamond mines of India was first given to Elisabeth Farnese, daughter of the Duke of Parma, in 1715 when she married Philip V of Spain.
It was passed down through more than seven generations and, as their descendants married into other European families, it travelled from Spain to France, Italy and Austria.
"All this time, it was hidden away in a royal jewellery box. Except for close relatives, and of course the family jewellers, no one knew about its existence," Sotheby's said.
The stone will appear in Sotheby's Geneva Jewellery sale on 15 May.
Reporting by Olive Enokido-Lineham; editing by Stephen Addison