Comparative study of five varieties of spodumene through optical absorption

A comparative study of five varieties of spodumene crystals from Brazil through optical absorption spectroscopy, classified according to the colours lylac, colourless I, colourless II, yellow and green is reported. This series shows a consistent increase of the [Fe]/[Mn] ratio. The principal bands in the yellow sample are at 7,000 and 9,000 cm-1, and in the green sample besides these bands a band at 16,000 cm-1 is observed. In lylac, colourless I and colourless II samples, the principal bands are at 18,000 cm-1 and when irradiated two new bands appears at 15,700 cm-1 (E perpendicular to c) and 11,000 cm-1 (K perpendicular to c). It is suggested that in green and yellow samples the bands are due to Fe2+ (at 7,000 cm-1 and 9,000 cm-1) and due to Fe2+ - Fe3+ charge transfer (at 16,000 cm-1). In lylac and colourless I samples the model for Mn3+ at two different sites is applied. The colourless II corresponds to the case in which Mn3+ is at one site alone, being prohibited from occupying the second site due to higher Fe concentration. (Author)