ROBERTO DE GUGLIEMO / SCIENCE PHOTO LIBRARY ROBERTO DE GUGLIEMO / SCIENCE PHOTO LIBRARY
Bi-coloured tourmaline crystals. Tourmaline is a complex silicate of aluminium and boron which occurs in many colours, including black, brown, blue green red and pink. Bi-coloured crystals such as these are fairly common. This specimen measures 18 x 7 cm and was found in Veadinho's Mine, Marilac, Brazil.
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