hard coal 55 mining engineering 16 coal 15 brown coal 14 metallurgy 9 deep mining 8 analytical chemistry 7 more ... history 7 mining 7 deposits mining 6 mines (mining) 4 safety of work 3 mine exploitation 3 caustobiolite deposits 3 environment 3 tar 2 firedamps 2 mine fires 2 coal energy sources 2 thrift 2 coke industry 2 mineral deposits 2 museums 2 protective pillars 2 landscape recultivation 2 crude oil 2 coal seams 2 closing 2 academic theses 2 inorganic chemistry 1 less ...