MARK SYKES / SCIENCE PHOTO LIBRARY MARK SYKES / SCIENCE PHOTO LIBRARY
Amethyst crystals. Amethyst is a variety of quartz (silicon dioxide), the most abundant mineral in the Earth's crust. The purple colour is caused by impurities of iron or manganese. Amethyst is found in Europe, the Americas and Africa, with the finest specimens occurring in Mexico and South America. Amethyst is popular amongst jewellers and mineral collectors.
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