Correlation between the Radiation Induced Colours and the OH-stretching Vibrations of Amazonite

The colours of many feldspars are enhanced by natural radiation. The same phenomenon can be simulated by X-ray radiation in the laboratory. The changes of colour and the formation of defect centers in different feldspars including one microcline (amazonite) after X-ray irradiation has been investigated using e.p.r. spectroscopy [1]. The main colours of amazonite are green, bluish green and blue. According to [2] they are caused by P b 3 + , which is produced by the reaction of radiation induced Pb 2 + with radiation induced dissociation products of structurally bound water. The present note deals with the changes of the OH-stretching vibrations and the colours of amazonite caused by X-ray radiation. Six samples of green, greenish blue and blue amazonite were X-ray irradiated (Mo-target/80 kV and 30 mA). The thickness of the samples was about 0.05 mm. All of them became darker after irradiation. The IR-transmission spectra of the samples were measured using an FTIR-spectrophotometer (PerkinElmer, Model 1760). All of the samples contained structural water, as was revealed by their IR-transmission spectra. The green and greenish blue amazonites show two distinct absorption bands at 3698 and 3622 c m " 1 due to OH-stretching vibrations, and one absorption band at 3420 cm" \ which indicates the presence of H-bonded OH. The IR-transmission spectra of the blue ama-