Abstract

Journal of Near Infrared Spectroscopy
Volume 16 Issue 4, Pages 399–407 (2008)
doi: 10.1255/jnirs.808

An application of near infrared spectroscopy to the study of the selenite minerals: chalcomenite, clinochalcomenite and cobaltomenite

Ray L. Frost,* B. Jagannadha Reddy and Eloise C. Keeffe
Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. E-mail: r.frost@qut.edu.au

The selection of five naturally occurring selenite minerals that contain two different transition metal ions, Cu2+ and Co2+could be distinguished by near infrared spectroscopy. Dependence of composition on spectral properties is a key to mineral identification and differentiation of the members of the selenite group. The nature of the band positions and splitting of band components in the electronic spectra of Cu2+ selenites in the region 12400–8000 cm–1 are in conformity with octahedral geometry distortion. The two split components which are observed for the Co2+ band near 9000 cm–1 in cobaltomenites are considered as the vibrational satellites of spin-allowed transition 4T1g(F) → 4T2g(F). Bands observed at 6950 cm–1, 6810 cm–1 and 6700 cm–1 are the overtones of OH stretches of structural water in selenites and a strong absorption feature near 6700 cm–1 is the result of hydrogen bonding between (SeO3)2– and H2O. These bands are shifted in cobaltomenites. A sharp absorption band at 5170 cm–1 is a common feature in all the spectra of selenite minerals and is the contribution by the combinations of the OH vibrations of water molecules, ν3 and ν1. A series of overlapping bands around 4500 and 4100 cm–1 is the result of the combination of the vibrational modes of (SeO3)2– ion in the minerals.

Keywords: chalcomenite, clinochalcomenite, cobaltomenite, NIR spectroscopy, Cu and Co- selenite minerals

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