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American Mineralogist; April 2004; v. 89; no. 4; p. 610-613
© 2004 Mineralogical Society of America
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The crystal structure of painite CaZrB[Al9O18] revisited

Thomas Armbruster1,*, Nicola Döbelin1, Adolf Peretti2, Detlef Günther3, Eric Reusser4 and Bernard Grobéty5

1 Laboratorium für chemische mineralogische Kristallographie, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
2 GRS Gemresearch Swisslab Ltd., Hirschmattstrasse 6, CH-6003 Luzern, Switzerland
3 Laboratory of Inorganic Chemistry—Elemental and Trace Analysis ETH Hönggerberg, HCI, G113, CH-8093 Zürich, Switzerland
4 Institute of Mineralogy and Petrography, Sonneggstrasse, 5 ETH Zentrum, CH-8092 Zürich, Switzerland
5 Department of Geosciences, University of Fribourg, Pérolles, CH-1700 Fribourg, Switzerland

Correspondence: * E-mail: thomas.armbruster{at}krist.unibe.ch

The crystal structure of the rare hexagonal mineral painite [a = 8.724(1), c = 8.464(2) Å] from Mogok (Myanmar), with the ideal composition CaZrB[Al9O18], was re-determined by single-crystal X-ray diffraction. Structure refinements were performed in space groups P63/m and P63. The centrosymmetric P63/m model yielded excellent agreement (R1 = 1.44%, 1189 reflections > 2{sigma} Iobs, 54 parameters) with the observed diffraction data without any unusual atomic displacement parameters, thus the acentric P63 model was rejected. A previous structural study claimed that painite was noncentrosymmetric and differed from the related structures of jeremejevite B5[{square}3Al6(OH)3O15] and fluoborite B3[Mg9(F,OH)9O9] in having lower symmetry.

The structure of painite comprises a framework of AlO6 octahedra that features two types of channels parallel to the c axis. One channel has a trigonal cross-section and is occupied by threefold coordinated B and Zr in sixfold prismatic coordination. The other channel has a hexagonal cross-section and is occupied by Ca. Chemical analysis by laser-ablation inductively-coupled plasma-mass spectrometry indicated that the crystal studied has significant substitution of Na for Ca (ca. 20%) charge-balanced by Ti4+ replacing octahedral Al leading to the formula Ca0.77Na0.19Al8.80Ti0.19Cr0.03V0.01Zr0.94Hf0.01B1.06O18.




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E. Makovicky and L. A. Olsen
High-pressure Al-rich hexagonal phases--What are their kin?
American Mineralogist, October 1, 2008; 93(10): 1585 - 1587.
[Abstract] [Full Text] [PDF]


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