There are over 300 naturally occurring manganese (Mn) minerals, but by far the most economically important are the manganese oxides psilomelane, cryptomelane, pyrolusite and wad (manganiferous earth). Traded ores and concentrates normally contain at least 38% manganese. Ninety-eight percent of the world’s output is made into additives for metal industries, mostly the iron and steel industry in which ferro-manganese and silico-manganese additives are used for their sulphur fixing and deoxidising properties. Manganese adds strength and toughness to iron. Another important use is in dry cell batteries, where MnO 2 contents of 70–80% are a general requirement. Other uses are as an oxidant in the purification of water, in acid leaching of certain ores (such as uranium), as a colourant in bricks, ceramics and paints, in fertiliser, animal feed and welding rods, and in the manufacture of ferrite and potassium permanganate.