The effect of thermal treatment on the 57Fe Mössbauer spectrum of beryl

• Published in: Physics and chemistry of minerals Vol. 33; no. 3; pp. 161 - 166
• Main Authors: da Costa, Geraldo Magela, de Oliveira Polli, Gabriel, Kahwage, Márcio A., de Grave, Eddy, Sabioni, Antônio Claret Soares, Mendes, Júlio Cesar
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01.05.2006
• Subjects: Beryllium aluminum silicates; Crystallography; Heat treatment; High temperature; Iron; Iron 57
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-006-0064-3

Mössbauer spectra (MS) of blue, green and yellow beryl (ideally Be3Al2Si6O18) containing approximately 1% of iron were obtained at 295 and 500 K. Room temperature (RT) spectra of both blue and green samples showed the presence of an asymmetric Fe2+ doublet (ΔEQ~2.7 mm/s, δ~1.1 mm/s), with a very broad low-velocity peak. There is no clear evidence for the presence of a ferric component. The MS of the yellow sample at RT consists of an intense central absorption with parameters typical for Fe3+ (ΔEQ~0.4 mm/s, δ~0.29 mm/s), plus an apparently symmetrical Fe2+ doublet. This sample acquires a light-blue shade upon heating in air at about 620 K. Thermal treatments at high temperatures caused no significant changes in the MS, but the green and yellow beryl acquire a blue colour. All these results are interpreted in relation to the existence of channel water and the distribution of iron among the available crystallographic sites.