Coal has been in the news lately, and the story hasn’t been pretty for the dirty fuel. The two U.S. presidential candidates have drawn each other into a debate about how anti- or pro-coal the other is. Meanwhile, The Financial Times reported on Friday that the once powerful Australian coal industry is in trouble. But for curious investors who are wondering if there are any bargains to be had in the sector, it’s worth remembering that not all coal is created equal.