[1/5] A view of the MP Materials rare earth open-pit mine in Mountain Pass, California, U.S. January 30, 2020. Picture taken January 30, 2020. REUTERS/Steve Marcus/File photo Aug 2 (Reuters) - Refining rare earths for the green energy transition is hard. Just ask MP Materials and Lynas. The world's two biggest rare earths companies outside of China are facing challenges turning rock from their mines into the building blocks for magnets used across the global economy, from Apple's (AAPL.O) iPhone to Tesla's (TSLA.O) Model 3 to Lockheed Martin's (LMT.N) F-35 fighter jet. The West's push to develop independent supplies of...