Study on Color-causing Elements in Qinghai Nephrite by Elemental Analysis and Electron Paramagnetic Resonance Spectroscopy

Abstract

BACKGROUND Color 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. OBJECTIVES To reveal the color-causing elements of eight colors of nephrite from Qinghai based on the relationship between analysis data and hue changes. METHODS X-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. RESULTS The 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. CONCLUSIONS This 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.

Keywords

• qinghai nephrite
• electron paramagnetic resonance
• color-causing elements
• fe