China state media reports suggest the country is considering limiting exports of "rare earths" as the trade war with the U.S. escalates.

Rare earths are a group of 17 elements used in everything from mobile phone cameras and automobile catalytic converters to wind turbines and MRI machines.

Rare earths aren't rare per se, but their distribution in the planet's crust makes processing them difficult.

China dominates the global supply of rare earths and accounted for almost 80% of exports to the U.S. last year.

As trade tensions between Washington and Beijing intensify, China's state media on Wednesday suggested it may play a new card -- restricting U.S. access to "rare earths," the chemical elements that are widely used in everything from mobile phones and other consumer electronics to wind turbines, MRI machines and military hardware.

China dominates global exports of the 17 elements that constitute rare earths, accounting for almost 80 percent of America's imports last year, according to the U.S. Geological Survey (USGS) and Bank of America Merrill Lynch analysts. Other countries that supply rare earths to the U.S. include Australia, Estonia, France and Japan.

Here's a look at what rare earths are and why they could play an important role in the ongoing trade war between the U.S. and China.

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Rare earths aren't that rare

The 17 elements defined as rare earths aren't as rare as their moniker suggests -- gold, copper and platinum are more abundant and easier to mine, for instance. By contrast, rare earths are ubiquitous in modern life, and their use is likely to spread as technology advances.

Cerium, used in compounds for catalytic converters in automobiles, is the most abundant and is more common in the earth's crust than copper or lead, according to the USGS.

The glass industry is the largest consumer of rare earths, which are used for polishing, additives for color and other special optical properties. One rare earth element, lanthanum, makes up as much as 50 percent of digital camera lenses, including cell phone cameras.

Irina Ivanova/CBS MoneyWatch

So where does the name come from?

Rare earths don't get their name because of their scarcity; rather, they got that label in the 18th and 19th centuries because of their relative imperviousness to heat compared with other mined materials.

Rare earths are found in such low concentrations around the world that they are harder to extract and refine, and not always found in commercially mineable quantities. As a result, a handful of countries account for the bulk of extraction, including China, Australia, Japan and Malaysia.

China, which has roughly 40 percent of the global reserves of rare earths, accounted for almost 80 percent of U.S. imports of the elements last year, according to Bank of America Merrill Lynch. One reason China is the global leader -- it's been pulling rare earths out of the ground for a long time. The country spent a century perfecting the refining method for extracting and refining rare earths in large enough quantities to keep costs manageable.

China's not-so-veiled threat

Chinese president Xi Jinping last week visited the country's biggest rare-earths producer in an appearance that was broadcast on Chinese national television. The visit followed a U.S. crackdown on technology giant Huawei by President Donald Trump's administration earlier this month, and was interpreted by experts as a signal that the Chinese government is weighing restrictions on rare-earth exports.

China will try to meet global rare-earths demand as "long as they are used for legitimate purposes," stated a commentary in the Xinhua news agency, a mouthpiece for Beijing. But later it added that "if necessary, China has plenty of cards to play."

Hu Xijin, editor in chief of China's Global Times newspaper, was blunter, saying in a tweet on Tuesday that the country is "seriously considering restricting rare exports to the U.S."

JJ Kinahan, chief marketing strategist at TD Ameritrade, said China's threat to use rare earths as a weapon against the U.S. is worrisome. "What it shows to me is that there is a little bit of a worsening relationship here," he said. "They went pretty deep in the bag to throw out something that would hurt."

A complete ban is impractical

Despite China's dominance in producing rare earths, implementing a total ban on exports to the U.S. might not be in its favor. For one, cutting off supplies of a critical material used in products around the world could undermine Beijing's efforts in recent years to portray itself as a responsible actor on the global stage -- and make it harder to bash the Trump administration for its hardball stance on trade.

Meanwhile, a Chinese ban risks inviting other countries to rev up rare-earths production. The last U.S. source for rare earths, the Mountain Pass Quarry in California, closed in 2015. The U.S. could shift demand for some metals to places like Malaysia or re-start domestic processing, although that could prove difficult because of regulations designed to prevent widespread environmental damage.

If China does clamp down, they are likely to be selective in which elements to target because the country wants to be seen as playing by World Trade Organization rules, said Arthur Kroeber, head of research at Gavekal Economics and editor-in-chief of China Economic Quarterly, on a call with clients this week. China's goal is to paint the U.S. as a "lawless actor" that disrupts economic growth, he said.

"I really think that they have a problem [in] that none of the options are very good and all of them involve very significant costs to China," Kroeber said. "So if they're going to do any of them they have to do them extremely carefully, and I think quite selectively."

The WTO would disapprove

Still, it wouldn't be the first time China tried to use its dominance in rare earths as part of a trade conflict. China blocked some rare-earth exports to Japan after a maritime dispute in 2010. That led some countries to search for alternatives -- and a protest by Japan with the WTO, which ruled in 2014 that the restrictions on rare-earth exports were illegal.

It also led some companies to cut their use of rare earths and to find alternatives for things like the element dysprosium, used in electric car magnets, the Bank of America analysts noted.

The Associated Press contributed to this report.