This bag will give you a clue as to what manganese dioxide, MnO2, is mainly used for. Staining bricks.
Ceramic materials are employed in the ceramic industry to make glazes, bodies, engobes and refractories. We study them at the mineral, chemical and physical levels.
Manganese in Clay Bodies
Manganese is used to stain clays (using black) and to impart fired speckling (as a decorative effect). It is dangerous?