MARTIN BOND / SCIENCE PHOTO LIBRARY MARTIN BOND / SCIENCE PHOTO LIBRARY
Quartz crystals. View of rock crystals, hexagonal prisms of quartz. Quartz (silicon dioxide) is colourless when pure, but the presence of impurities can give a range of colours including white, pink, yellow, blue, green and smoky brown. Quartz is one of the commonest minerals of the earth's crust, comprising about 12 percent by volume.
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