Koktokay No. 3 mine vein of Fuyun County in northwest China's Xinjiang Uygur Autonomous Region has the largest beryllium resources in the world. As the forth chemical element in the periodic table, beryllium is a hard grey metal found mainly in the beryl mineral. Named after beryllos, the Greek name for the beryl mineral, it literally means the "color of the ocean." What is beryl? What is beryllium used for? And why has Koktokay No. 3 mine vein remained absent from maps for a long time? CGTN's Zang Shijie talks to a retired mine worker at the mine vein.