The Polar Star is a 41.28-carat diamond, prized by Joseph Bonaparte and later the aristocratic Russian Yusupov dynasty. It was sold by Cartier to Lady Deterding in 1928.
The Polar Star diamond was discovered in the celebrated Golconda mines. Toward the late eighteenth century, a lapidary cut the rough stone into a cushion-shaped diamond whose perfect symmetry included a pavilion in the form of an eight-pointed star, giving the gem both its sparkle and its name.
Weighing 41.28 carats, the diamond became part of the treasure of Joseph Bonaparte (1768–1844), elder brother of Napoleon Bonaparte (1769–1821), who named Joseph king of Naples and later king of Spain. Joseph sold the stone after having lost his kingdom, in order to finance his exile to America.
The Polar Star was then bought by Princess Tatiana Yusupov, and remained in that grand Russian dynasty for about a century.
In 1917, when the Russian Revolution was brewing and the aristocracy was threatened, Princess Zinaida Yusupov and her son Felix (famous for having organized the execution of Rasputin) fled abroad, taking the precious diamond in their luggage. As old clients of the Cartier brothers, they deposited the gem—along with several other jewels—with Pierre Cartier, who headed the New York branch.
The Polar Star was later transferred to Cartier London and set in a diamond and emerald necklace sold in 1928 to Lady Deterding, wife of the founder of the Shell Oil Company. At her death in 1980 the diamond was bought by a dealer.