Dissymetrization in tourmaline: 

the atomic arrangement of sectoral-zoned triclinic Ni-bearing tourmaline

John M. Hughes

Department of Geology, The University of Vermont, Burlington, VT 05405, U.S.A.

John Rakovan

Department of Geology, Miami University, Oxford, Ohio 45056, U.S.A.

Andreas Ertl

Institut für Mineralogie und Kristallographie, Geozentrum, Universität Wien, Althanstrasse 14, 1090 Vienna, Austria

George R. Rossman

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125-2500

Ivan Baksheev

Geology Department, Lomonosov Moscow State University, Vorobiovy Gory, Moscow 119992, Russia

Heinz-Jürgen Bernhardt

Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44801 Bochum, Germany


 The tourmaline atomic arrangement is one of the last rock-forming silicate structures to be investigated in detail. Although putatively possessing hexagonal R3m symmetry, reports of optically-anomalous tourmaline are common, and recently an occurrence of triclinic tourmaline was reported with dissymetrization resulting from non-equivalency of the occupants of the tourmaline Y-sites. We here report the atomic arrangement of a Ni-bearing tourmaline from the Middle Urals, Russia, in non-conventional triclinic space group R1 (R = 4.41%) to facilitate comparison with the conventional R3m cell. The dissymetrization occurs as a result of inequalities of the hexagonal Y and Z tourmaline sites, in contrast to the single previous structure study. The atomic arrangement demonstrates that the tourmaline atomic arrangement is robust, and is capable of incorporating various substituents by modifying the putative structure in lower symmetries, suggesting that further exploration of tourmaline’s role in trace-element variation is warranted.

Optical studies demonstrate a 2V greater than zero. Spectroscopic studies show the optical absorption spectrum of the Ni-tourmaline has strong absorptions in the 400, 600-700, and 1100 nm regions, in addition to OH features near 1450, 2300, and 2700 nm. It is concluded that the color in the E perpendicular to c polarization comes dominantly from Fe mixed-oxidation-state couples, and from Cr3+. Contributions from the nickel are believed to be minor and will fall in the regions of strong Cr and Fe absorption.


The slice of tourmaline from the Berezobskoe gold deposit used for the optical spectroscopy in two polarizations

Spectroscopic data files:

E parallel to c
E perpendicular to c

last updated: 8-Nov-2009