The mineral, Pyrolusite, is the most important ore mineral of MANGANESE, forms dark gray to black coatings, crusts, columnar or granular masses, and rare crystals (polianite) that have one perfect cleavage. Pyrolusite results from alteration of MANGANITE and other manganese minerals. About 95% of the world's annual production of manganese is used by the iron and steel industry to purify iron and to make alloys. Manganese is added to iron because it reduces iron oxide to form manganese oxide, which dissolves well in molten slag and is easily separated from the iron. In alloys, manganese increases the durability and corrosion resistance of iron and steel and makes steel more malleable when forged. This nonmagnetic, tough, durable, and shockproof alloy is used in grinding machinery, wrecking equipment, caterpillar trucks, and mechanical pounding equipment used in heavy-duty construction. The iron manganese alloys, which are used for making other alloys, are ferromanganese (about 80% Mn) and spiegeleisen (15-30% Mn); they contain some carbon and silicon. Other important manganese alloys that do not contain iron include the Heusler alloys (18-25% manganese plus copper and aluminum or zinc), which are the strongest nonferrous metals; manganese copper (approximately 75% copper and 25% manganese), which has great electrical resistance; and manganin (about 83% copper, 14% manganese, and 3% nickel), which has a very slight heat-expansion coefficient and an electrical resistance nearly independent of temperature. Alloys very rich in manganese and containing nickel and copper have a high heat-expansion coefficient, however, and are used in the expanding part of bimetal thermostats. Manganese chloride and manganese sulfate, are added to commercial fertilizers. The sulfate is sometimes used for making red enamel, for impregnating wood, and for staining zinc black. Manganese carbonate yields the pigment manganese white. A number of manganese salts are used in the paint industry to accelerate the hardening of drying oils. When a manganese compound is fused with potassium nitrate, the intensely green potassium manganate is produced. By adding sulfuric acid, the intensely purple potassium permanganate is obtained. Potassium permanganate is used for bleaching and removing color from fabrics that are able to tolerate strong oxidation. In concentrated form such solutions are also used to clear clogged drain pipes. The most important manganese compound, pyrolusite or manganese dioxide, is also an oxidizing agent. Pyrolusite is used extensively in the electrodes of dry batteries, where it absorbs liberated hydrogen gas and then chemically bonds it. It is also used as an oxygen source in fireworks and as a chemical catalyst. All other manganese compounds are made from pyrolusite.