DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Small fragments of the mineral tourmaline, all illustrative of the columnar/prismatic habitat of the crystals and the variety of colours they come in, ranging from pink and reddish hues to green and bluish as well as opaque black. Chemically tourmaline is a complex boron silicate having a trigonal crystal system. It is formed in deep-seated igneous rocks. Tourmaline is a semi-precious gemstone, and clear stones are much used in jewelry.
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