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Optical spectroscopic study of tetrahedrally coordinated Co2+ in natural spinel and staurolite at different temperatures and pressures
-
Michail N. Taran
,
Monika Koch-Müller
Veröffentlicht/Copyright:
1. April 2015
Abstract
Optical absorption spectra of natural Co-bearing spinel and staurolite were studied at different temperatures and pressures. In both minerals, two broad, intense structured bands in the range 5500-8000 and 15 000-19 000 cm-1, caused by electronic spin-allowed transitions 4A2 → 4T1(4F) and 4A2 → 4T1(4P) of IVCo2+ are the predominant absorption features. In addition, in both cases broad bands, derived from spin-allowed electronic transitions 4E → 4T2 of IVFe2+, appear in the near infrared range partly overlapping the bands caused by IVCo2+. In staurolite the NIR range of the spectra are complicated by intense sharp lines of OH-vibrations at around 3400 cm-1.
In spinel, with a regular tetrahedral site, the splitting of the spin-allowed bands I and II of IVCo2+ is assumed to be caused by spin-orbit and vibronic coupling. In staurolite, the splitting is stronger due to the additional low-symmetry crystal field effect of IVCo2+. It is found that the effect of temperature and pressure on the behavior of the 4A2 → 4T1(4P) bands of IVCo2+ in the two minerals are rather similar, in contrast to our findings for the spin-allowed bands of IVFe2+ in spinel and staurolite. This is interpreted as a manifestation of a dynamic Jahn-Teller effect for IVFe2+ and lack of it in case of IVCo2+
Keywords: Spinel; staurolite; tetrahedral coordination; Co2+; optical absorption spectra; temperature and pressure effects
Received: 2009-3-17
Accepted: 2009-7-21
Published Online: 2015-4-1
Published in Print: 2009-11-1
© 2015 by Walter de Gruyter Berlin/Boston
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Schlagwörter für diesen Artikel
Spinel;
staurolite;
tetrahedral coordination;
Co2+;
optical absorption spectra;
temperature and pressure effects
Artikel in diesem Heft
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- Chemical substitutions, paragenetic relations, and physical conditions of formation of högbomite in the Sittampundi layered anorthosite complex, South India
- Miguelromeroite, the Mn analogue of sainfeldite, and redefinition of villyaellenite as an ordered intermediate in the sainfeldite-miguelromeroite series
- Mechanism and kinetics of a mineral transformation under hydrothermal conditions: Calaverite to metallic gold
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