Beijing’s veiled threats to restrict exports of rare earth metals to the US have been called by many as one of China's nuclear options in a trade conflict with Washington. The US relies on China for about 80 percent of its rare earths supplies. The metals are used in everything from electric car motors and electronics to oil refining. They are also vital for US national security, as they are used in many major weapons systems.

Washington has reportedly started exploring opportunities to purchase rare earth metals from African countries, but they cannot provide the volume that China can. Beijing's reserves account for roughly 30 percent of the world's total, and the country dominates global supply chain as it produces more than 80 percent of them.

Rare earth metals are a group of 17 chemical elements, namely gadolinium, holmium, dysprosium, europium, ytterbium, lutetium, neodymium, praseodymium, promethium, samarium, terbium, thulium, cerium, erbium, scandium, yttrium and lanthanum. Technically they are not rare but very difficult to find in large concentrations, and hard to process as the ores often contain naturally occurring radioactive materials.