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Zinc oxide is an inorganic compound with the formula ZnO. Synthetic ZnO is primarily used as a white powder that is insoluble in water, or naturally as the mineral zincite. The powder is widely used as an additive in numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g., car tires), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient), batteries, ferrites, fire retardants, and first aid tapes. ZnO occurs as white powder known as zinc white or as the mineral zincite. The mineral usually contains manganese and other impurities that confer a yellow to red colour. Crystalline zinc oxide is thermochromic, changing from white to yellow when heated and in air reverting to white on cooling. This colour change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x = 0.00007. Zinc oxide is also an amphoteric oxide. It is nearly insoluble in water and alcohol, but it is soluble in (degraded by) most acids, such as hydrochloric acid.