Mn-rich tourmaline from Austria:

structure, chemistry, optical spectra, and relations to synthetic solid solutions

Andreas Ertl

Institut fur Mineralogie und Kristallographie
Geozentrum, Universitat Wien
Althanstrasse 14, A-1090 Vienna, Austria

John M. Hughes

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

Stephan Prowatke

Mineralogisches Institute, Universitat Heidelberg
Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany

George R. Rossman

Division of Geological and Planetary Sciences
California Institute of Technology, MS 170-25, Pasadena, CA 91125-2500, U.S.A.

David London

School of Geology and Geophysis, University of Oklahoma
100 East Boyd Street, Room 810 SEC, Norman, OK 73019, U.S.A.

Eric A. Fritz

3541 Paseo de Francisco #240
Oceanside, CA 92056, U.S.A.

Submitted to American Mineralogist

ABSTRACT

Mn-rich tourmalines with MnO contents in the range 8-9 wt% MnO (~ 0.1 wt% FeO) from a recently discovered locality in Austria, near Eibenstein an der Thaya, Lower Austria, have been characterized by crystal structure determination, by chemical analyses (EMPA, SIMS), and by optical absorption spectroscopy. For these Mn-rich and Li-bearing olenite samples, the crystal structure determinations in combination with the chemical analyses give the optimized formulae

^X(Na_0.799Ca_0.011K_0.002&127_0.188) ^Y(Al_1.278Mn²⁺_1.212Li_0.371Fe²⁺_0.021Ti_0.003Mg_0.002&127_0.113) ^ZAl₆ ^T(Si_5.799Al_0.201) B₃O₂₇ [(OH)_3.255F_0.425O_0.320],

with a =15.9466(3) Å, c = 7.1384(3) Å and R = 0.036 for the sample with ~ 9 wt% MnO, and

^X(Na_0.773Ca_0.032K_0.004&127_0.191) ^Y(Al_1.233Mn²⁺_1.142Li_0.483Fe²⁺_0.019Ti_0.006Mg_0.002Zn_0.002&127_0.113) ^ZAl₆ ^T(Si_5.826Al_0.174) B₃O₂₇ [(OH)_3.330F_0.480O_0.190]

for a sample with a =15.941(1) Å, c = 7.136(1) Å, R = 0.025 and ~ 8 wt% MnO. The refinements show 1.22-1.25 Al at the Y site. While the Mn content increases, the Li and the F content decrease. The Li content (0.37-0.48 apfu) is similar to, or lower than, the Li content of olenite (rim-composition) from the type locality, but these Mn-rich tourmalines do not contain ^[4]B. Like the tourmaline from Eibenstein an der Thaya, synthetic Mn-rich tourmaline (in a Li + Mn-bearing system), containing up to ~ 0.9 apfu Mn (~ 6.4 wt% MnO), is aluminous but not Li-rich. This study demonstrates that although a positive correlation exists between Mn and Li (elbaite) in tourmaline samples from some localities, this coupling is not required to promote compatibility of Mn in tourmaline. The lattice parameter, a, in Mn-rich tourmalines (MnO: >3 wt%) is largely a function of the occupants (refined Al) at the Y site (r² = 0.971).

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