Table of Contents
International Journal of Mineralogy
Volume 2014, Article ID 648530, 11 pages
http://dx.doi.org/10.1155/2014/648530
Research Article

X-Ray Diffraction and Vibrational Spectroscopic Characteristics of Hydroxylclinohumite from Ruby-Bearing Marbles (Luc Yen District, Vietnam)

1Geological Institute, Slovak Academy of Sciences, Dubravska cesta 9, 840 05 Bratislava, Slovakia
2Mineralogy Department, Institute for Geosciences, Friedrich-Schiller University, 077 45 Jena, Germany
3Institute of Inorganic Chemistry, Slovak Academy of Sciences, 840 05 Bratislava, Slovakia
4Department of Mineralogy and Petrology, Comenius University, 842 15 Bratislava, Slovakia
5Helmholtz Center Geoforschungs Zentrum, 144 73 Potsdam, Germany
6AGH University of Science and Technology, Faculty of Geology, Geophysics and Environment Protection, 30-059 Krakow, Poland
7Geological Institute, Slovak Academy of Sciences, 974 01 Banská Bystrica, Slovakia

Received 28 June 2013; Accepted 22 October 2013; Published 29 January 2014

Academic Editors: Makoto Arima, Ana Isabel Becerro, J. Du, and B. Tsikouras

Copyright © 2014 V. Hurai et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A honey-yellow hydroxylclinohumite from ruby-bearing marbles of the Luc Yen district in northern Vietnam was characterized by electron microprobe (EPMA), single-crystal X-ray diffraction (XRD), micro-Raman, and Fourier-transform infrared (FTIR) spectroscopy. The studied crystals correspond to nearly ideal clinohumite with the structural formula 4[Mg2SiO4][(Mg,Fe,Ti)(OH,F)2] and roughly equal F and OH proportions. Crystal structure analysis showed Ti substitution for Mg only at the Mg3 site. A Fourier-difference map revealed one hydrogen site associated with ninth oxygen atom. The calculated O–H bond distance was shorter than that in other natural clinohumites. FTIR revealed bands corresponding to combination of OH-stretching with Mg–OH and/or Fe–OH bending modes, combinations of OH and Fe–OH vibrations, combination of fundamental bands of the Si–OH bonding, combination of OH and Si–OH vibrations, and first (2) and the second (3) overtones of the OH-stretching vibration mode. Two groups of OH-stretching vibration and FTIR absorption bands at 3390–3420 cm−1 and 3560–3580 cm−1 show reversible temperature-dependent shift. The low-frequency bands absent in pure synthetic hydroxylclinohumites are assigned to OH-planar defects caused by Ti-for-Mg substitution.