MARK WILLIAMSON / SCIENCE PHOTO LIBRARY MARK WILLIAMSON / SCIENCE PHOTO LIBRARY
A sample of a white Calcite (calcium carbonate, CaCO3) crystal containing particles of pyrite, also known as fool's gold (iron disulphide, FeS2). Photographed at Focus Terra, the Earth Science Research and Information Centre of ETH, the Swiss Federal Institute of Technology, Zurich.
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