From the same article posted by Jim23 May 2019 20:32
Rare earth elements are sometimes described as the “vitamins of chemistry,” as small doses produce powerful salutary effects. A sprinkle of cerium here and a pinch of neodymium there makes TV screens brighter, batteries last longer, and magnets stronger. If China suddenly shut off access to these materials, it would be like rewinding the tech industry back a few decades. And no one wants to ditch their iPhone and go back to a BlackBerry.