For years, the Chinese government has worked to control the export of rare earths, a group of metals used in an array of products, as common as semiconductors and lights. Now, in its trade war with the United States, China is moving to limit the market for these metals even further, which could have disastrous consequences for American manufacturing and military power. So, what exactly are these metals, and why are they so important?

What are rare earths?

There are 17 types of metals known as rare earths, which span the periodic table and are crucial to industries like technology, energy and transportation. With names like terbium, praseodymium and dysprosium, the metals are important ingredients for some of the most advanced technologies.

Rare earths can be sorted into two kinds: heavy and light. Heavy rare earths have a greater atomic weight and are typically more rare, meaning they sell in smaller quantities and are prone to shortages. Light metals, by contrast, have a lesser atomic weight. The two most important are neodymium and praseodymium, which are primarily used to create magnets.

What are they used for?

The uses for rare earths are expansive: semiconductor chips that power artificial intelligence; the motors of electric vehicles; fighter jets and guided missiles used by the U.S. military; wind turbines; and LED lights found in millions of households, among others.

Many rare earths have chemical properties that make them heat resistant, so they can be used to create high-quality magnets, glass, lights and batteries. Magnets made from rare earths are significantly more powerful — and valuable — than other types, especially in electric car production.

Does the United States produce rare earths?

The United States has just one operational rare earths mine, in Mountain Pass, Calif., which produces around 15 percent of global rare earths.