Manganese is a chemical element designated by the symbol Mn and atomic number 25. It is found as a free element in nature (often as combination with iron), and in many minerals. As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels. It makes up about 1000 ppm (0.1%) of Earths crust, making it the 12th most abundant element there. Manganese occurs principally as pyrolusite (MnCO2), braunite (Mn2+Mn3+6) (SiO12), psilomelane (Ba, H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3).