Synthetic B-rich olenite: correlations of single-crystal structural data

Andreas Ertl, Gerald Giester
Institut für Mineralogie und Kristallographie, Geozentrum, Universität Wien, Althanstrasse 14, 1090 Vienna, Austria

Thomas Ludwig, Hans-Peter Meyer
Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

George R. Rossman
Division of Geological and Planetary Sciences, California Institute of Technology,
Pasadena, California 91125, USA

ABSTRACT

Synthetic Al- and B-rich tourmaline crystals described by London (2011) were characterized further by SIMS and new EMP analyses. These tourmalines are the first synthetic B-rich olenites characterized by single-crystal X-ray diffraction, because they are significantly larger than synthetic samples produced in the past. The average final formulae are

^X(Na­_0.7ÿ_0.3) ^Y(Al_2.5Li_0.4Fe²⁺_0.1) ^ZAl₆ (BO₃)₃ [Si_5.2B_0.5Al_0.3O₁₈] ^V[(OH)_2.9O_0.1] ^W[O_0.9(OH)_0.1], with a = 15.765(1), c = 7.083(1) Å,

^X(Na­_0.7ÿ_0.3) ^Y(Al_2.5Li_0.5) ^ZAl₆ (BO₃)₃ [Si_4.8B_0.9Al_0.3O₁₈] ^V(OH)₃ ^W[(OH)_0.5O_0.5], with a = 15.746(1), c = 7.075(1) Å, and

^X(Na­_0.6Ca_0.1ÿ_0.3) ^Y(Al_2.3Li_0.5Fe_0.2) ^ZAl₆ (BO₃)₃ [Si_4.7B_1.2Al_0.2O₁₈] ^V(OH)₃ ^W[(OH)_0.9O_0.1], with a = 15.723(1), c = 7.068(1) Å.

The small <T-O> distances, down to 1.599 Å, reflect relatively high amounts of ^[4]B (up to ~1.2 apfu; refinements with R = ~2%). All these samples also contain significant amounts of ^[4]Al (~0.2 apfu). A pronounced negative correlation (r² = 1.00; only three data points) between temperature during crystal growth (at a constant pressure) and ^[4]B (from refinement) in these synthetic olenites was found.

Image of the overgrowth of B-rich olenite (pale area on top) on the seed-crystal.

Synthetic B-rich olenite at top of dark seed-crystal in two polarizations

Birefringence of the synthetic B-rich overgrowth - crossed polarizers

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last revised: 1-Jun-2012