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This ring is packed with 648 22cm-long neodymium magnets laced with another rare-earth element, dysprosium, which makes them much less liable to become demagnetised.

The price of dysprosium, a “heavy” rare-earth element used in magnets for car motors, almost tripled to $305 a kilogram.

"The country's grasp on the rare-earth element industry could one day give China a strong technological advantage and increase its military superiority," she wrote.

The company’s Mountain Pass mine, discovered in 1949 by uranium prospectors who noticed local radioactivity, dominated rare-earth element production through the 1980s.