New data on “kerolite–pimelite” series and the colouring agent of Szklary chrysoprase, Poland

Green clay and chrysoprase samples from the Ni-laterite deposit in Szklary, Poland, were studied by X-ray diffraction (XRD), electron microprobe analysis (EMPA), Raman, infrared and UV–VIS–NIR absorption spectroscopies. The clay samples proved to be Ni-rich “kerolite” and “pimelite”, and as these minerals are currently discredited, their nature was studied in more detail by high-temperature X-ray diffraction and thermal analysis coupled with mass spectrometry. These methods showed that “kerolite” and “pimelite” contain interlayer water, i.e. they differ from the non-hydrated talc–willemseite mineral series. Subsequently, the XRD and EMPA analyses of Szklary chrysoprase indicated that chrysoprase’s colouring agent is “pimelite”, which was further corroborated by Raman and UV–VIS–NIR spectroscopies. In addition, the Szklary chrysoprase, which has been quarried since the Middle Ages and used in jewellery and wall decorations (e.g. in the Prague Cathedral), was described from the gemmological point of view.