Occurrence. Manganese is found in nature chiefly as the dioxide MnO2, called pyrolusite. In smaller amounts it occurs as the oxides Mn2O3 and Mn3O4, and as the carbonate MnCO3. Some iron ores also contain manganese.
Preparation and properties. The element is difficult to prepare in pure condition and has no commercial applications. It can be prepared, however, by reducing the oxide with aluminium powder or by the use of the electric furnace, with carbon as the reducing agent. The metal somewhat resembles iron in appearance, but is harder, less fusible, and more readily acted upon by air and moisture. Acids readily dissolve it, forming manganous salts.
Oxides of manganese. The following oxides of manganese are known: MnO, Mn2O3, Mn3O4, MnO2, and Mn2O7. Only one of these, the dioxide, needs special mention.
Manganese dioxide (pyrolusite) (MnO2). This substance is the most abundant manganese compound found in nature, and is the ore from which all other compounds of manganese are made. It is a hard, brittle, black substance which is valuable as an oxidizing agent. It will be recalled that it is used in the preparation of chlorine and oxygen, in decolorizing glass which contains iron, and in the manufacture of ferromanganese.
Compounds containing manganese as a base-forming element. As has been stated previously, manganese forms two series of salts. The most important of these salts, all of which belong to the manganous series, are the following:
| Manganous chloride | MnCl2·4H2O. |
| Manganous sulphide | MnS. |
| Manganous sulphate | MnSO4·4H2O. |
| Manganous carbonate | MnCO3. |
| Manganous hydroxide | Mn(OH)2. |
The chloride and sulphate may be prepared by heating the dioxide with hydrochloric and sulphuric acids respectively:
MnO2 + 4HCl = MnCl2 + 2H2O + 2Cl,
MnO2 + H2SO4 = MnSO4 + H2O + O.