(a) Tectonically deformed coal with large-scale irregular friction mirror planes for sample XGZ; (b) fractures and friction mirror planes in sample QK; (c) well-developed friction mirror planes in sample TX10; (d) loose small coal particles in sample TX11; (e) scratches in sample TX23; (f) small-scale friction mirror planes in ...
View more: Discovery of the largest natural carbon onions on Earth