GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
Copper sulphide. Copper (II) sulphide (CuS) in a watch glass. Tarnished manganese (Mn) metal chunks in a watch glass. When exposed to air for a long time, manganese tarnishes (oxidizes) to manganese (II, III) oxide (Mn3O4). The oxide has an appearance similar to iron rust.
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