There are 17 rare earth elements. While almost all of them have vital industrial uses, you could be forgiven for believing, based on news coverage, that there are only four that matter: neodymium, praseodymium, dysprosium, and terbium.To be sure, those are the essential ingredients in the powerful permanent-magnet motors that go into electric vehicles, heating and cooling systems, appliances, tools, fighter jets, bombs, and many other systems. But the industrial and national-security importance ...