Brazil holds a trump card in tariff negotiations with the United States: its subsoil is rich in rare earth minerals coveted by manufacturers in a sector dominated by China. The South American giant holds the world's second-largest reserves of these elements used in everything from electric vehicles, solar panels and smart phones to jet engines and guided missiles. China, a US rival which like Brazil is in a tariff standoff with President Donald Trump's administration, holds a near-monopoly on rare earths production.