Pyrite is iron sulfide. It is also called fool's gold because it is a metallic gold color. Sparks will fly if it is hit with a hammer. It forms in cubes. It is not valuable by itself, but is often rich in gold and copper. Fossils are often replaced by pyrite.
Pyrite exposed to the atmosphere during mining and excavation reacts with oxygen and water to form sulfate, resulting in acid mine drainage. This is one of the biggest problems in mine cleanup.
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