ROBERT DE GUGLIEMO / SCIENCE PHOTO LIBRARY ROBERT 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. The specimen measures 6 x 2.5 cm and was found in Cruzeiro's Mine, Sao Jose da Safira, Brazil.
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