The world’s largest faceted blue topaz will soon be put on display in the London Museum.

Starting Oct. 19, a 9,381-carat blue topaz called “The Ostro Stone” will go on permanent display to the public in the London Natural History Museum’s Minerals gallery. It’s approximately 6 inches in length and 4 inches wide, with its deep blue color resulting from a treatment applied when it was in its rough state.

British gemstone pioneer and explorer Max Ostro discovered the stone in its natural form in 1960 in Minas Gerais, Brazil, and the topaz has been in the family vault ever since. It is being put on display now through a long-term loan from his son, Maurice Ostro, chairman of Ostro Minerals.