ROBERTO DE GUGLIEMO / SCIENCE PHOTO LIBRARY ROBERTO DE GUGLIEMO / SCIENCE PHOTO LIBRARY
Crystals of amethyst, a violet-hued variety of quartz. Quartz (silicon oxide) is colourless when pure, but the presence of impurities can give a range of colours including white, pink, yellow, blue, green, violet and smoky brown. This specimen measures 6 x 5.5 cm and was found in Irai, Rio Grande do Sul, Brazil.
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