The US trade war with China has a major sticking point: rare earths minerals. Last month, President Donald Trump said the United States needed Greenland “very badly,” renewing his threat to annex the Danish territory.

Rare earths are among the most critical raw materials on the planet, deeply embedded in the technologies that underpin modern life. Yet few people have heard of them or know what they do.

China has approved "a certain number" of export permits for rare earth elements and related items, its commerce ministry spokesman said on Thursday.