different classes of rocks are formed by different methods
metamorphic_rock is rock. rock is material. classic_and_rock is types_of_music. slate is not another_type_of_hard_rock. slate is metamorphic_rock. rock is natural_building_material. methods_of_rock_climbing is method. methods_of_rock_climbing is not method. slate is another_type_of_hard_rock. metamorphic_rock is stone.