Hope diamond, sapphire-blue gemstone from India, one of the largest blue diamonds known. It is thought to have been cut from a 112-carat stone brought to France by the jewel trader Jean-Baptiste Tavernier and purchased by Louis XIV in 1668 as part of the French crown jewels. This stone, later called the French Blue, was recut into a 67-carat heart in 1673 and disappeared after the crown-jewel robbery of 1792. The 45.5-carat Hope diamond, named for the London banker Thomas Hope, who purchased it in 1830, was apparently formed from it. The Hope diamond is on display in the Smithsonian Institution, Washington, D.C.