LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY
Quartz crystals. Close-up of quartz or silicon dioxide (SiO2), one of the commonest minerals in the Earth's crust (12% by volume). The pure, colourless variety is also known as rock crystal and is used as a gemstone and highly prized by collectors. When it contains impurities, these impart a range of colours including white, yellow, pink, blue, green and smoky brown.
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