To hear some U.S. officials tell it, Greenland is a treasure trove of crucial minerals ripe for the taking. Texas Sen. Ted Cruz, for example, has hailed how “Greenland sits atop vast reserves of rare-earth elements,” while U.S. Vice President J.D. Vance has pointed to the territory’s “incredible natural resources.” “It’s our national security. It’s critical minerals,” then-incoming U.S. National Security Advisor Mike Waltz declared when discussing President Donald Trump’s designs on the island last year. As Greenland has yet again entered the global spotlight amid Trump’s annexation threats, so too has the island’s mining potential for rare earths, the...