--Far beneath the rolling cropland of southeast Nebraska sits a deposit of elements that can be used to make steel and aluminum stronger.... The U.S. relies entirely on imports for 14, and foreign producers provide more than half the supply of another 14 substances, led by China. Recently, tight supplies caused prices to soar for the critical elements used in lightweight magnets for electric vehicles and other high-tech products.... Most of the U.S. supply comes from open pit mines in Brazil..