Study on Color-causing Elements in Qinghai Nephrite by Elemental Analysis and Electron Paramagnetic Resonance Spectroscopy
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ABSTRACT
BACKGROUNDColor is the important manifestation of nephrite value. Qinghai nephrite has different colors, but there is a lack of research on coloration. In recent years, the study on the coloration of nephrite in Qinghai mainly focused on azure-green and blue-violet, and it was considered that Cr3+ and Mn2+ were respective coloration elements of azure-green and blue-violet. The color of Qinghai nephrite is not a simple color, such as white-green, azure-green, and blue-violet. Therefore, Qinghai nephrite should contain a variety of color-causing elements.OBJECTIVESTo reveal the color-causing elements of eight colors of nephrite from Qinghai based on the relationship between analysis data and hue changes.METHODSX-ray Fluorescence Spectrometry (XRF), Chemical Titration, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Electron Paramagnetic Resonance Spectroscopy (EPR) were used to study the color-causing elements of nephrite.RESULTSThe color-causing element of white Qinghai nephrite was Fe3+. The color-causing elements of white-green and azure-green Qinghai nephrite were Fe2+ and Fe3+, respectively. The chromogenic elements of green Qinghai nephrite were Fe2+, Fe3+ and Mn in high valence. The color-causing elements of azure-green Qinghai nephrite were Fe2+, Fe3+ and Cr3+. The chromogenic elements of yellow and brown Qinghai nephrite were Fe3+ and high-valence Mn. Fe3+ and Ti4+ were the color-causing elements of blue-purple Qinghai nephrite.CONCLUSIONSThis study determined the color-causing elements of different colors of Qinghai nephrite, which provided a theoretical basis for the study of the coloration mechanism of Qinghai nephrite.
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