STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph (SEM) of fractured amethyst. Amethyst is a purple variety of quartz (SiO2) and owes its violet color to irradiation, iron impurities, and the presence of trace elements, which result in complex crystal lattice (periodic array of atoms) substitutions. Quartz is the second-most-abundant mineral in Earth's continental crust, after feldspar. Its crystal structure is a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2.The best varieties of amethyst can be found in Siberia, Sri Lanka, Brazil and the far East. The hardness of the mineral is the same as quartz, thus it is suitable for use in jewelry. Magnification: x800 when printed 10 centimetres wide.
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