(IDEX Online) - The Surat Diamond Bourse (SDB) finally opened on Tuesday (21 November) almost three years late.The $355m bourse (pictured) was originally supposed to open in January 2020, according to the SDB website. That was put back by September 2021, to 2022 and then to April of this yearIt has officially been recognized by Guinness World Records as the largest office building in existence (7.1 million sq. ft of floor space), eclipsing The Pentagon, HQ of the US Defense Department.Local media reported that 135 diamond trading firms started operations at their offices at the SDB, among them 26 traders who had moved from Mumbai's rival Bharat Diamond Bourse (BDB).Earlier this month Kiran Gems, described as the world's largest rough diamond manufacturer, said it was relocating its headquarters, together with 1,200 employees, from Mumbai to the new Surat Diamond Bourse (SDB). It has built a dedicated apartment complex for its workers and their families, a 10-minute drive from SDB.Prime Minister Narendra Modi is due to officially open the building on 17 December.