Micro-morphology and Mineral Composition of Different Color Qinghai Nephrites

Abstract

BACKGROUND Qinghai nephrites show different colors. In recent years, there have been a lot of studies on Qinghai nephrite mineralogy, but the studies on the mineral characteristics of Qinghai nephrite with different colors are lacking. OBJECTIVES To study the relationship between color and mineralogical features of Qinghai nephrites. METHODS Polarizing Microscopy, Scanning Electron Microscopy, Electron Probe Microanalyzer and Powder X-ray Diffraction were used to analyze the microtopography, microstructure, mineral composition and crystallinity of tremolite. RESULTS Tremolite in white, blue-violet and brown Qinghai nephrite are mainly fibrous and have micro-fiber blastic texture with crystallinity of 96.12%-96.88%. Tremolite in green-white and viridis Qinghai nephrite are mainly foliated, and has micro-foliated blastic texture with crystallinity of 97.35% and 97.32%, respectively. Tremolite in green and azure-green Qinghai nephrite are mainly foliated, and have microscopic blade-cryptocrystalline blastic texture with crystallinity of 95.48% and 95.29%, respectively. Tremolite in yellow Qinghai nephrite is mainly columnar, and has micro-columnar blastic texture and crystallinity of 97.84%. The main mineral different color Qinghai nephrite is tremolite, with content of more than 95%. Some minor minerals only appear in the specific color Qinghai nephrite, such as titanite in viridis Qinghai nephrite, anorthite in yellow Qinghai nephrite, magnesite in green Qinghai nephrite, chromite in azure-green Qinghai nephrite, and clinozoisite in brown Qinghai nephrite. CONCLUSIONS There are differences in mineral features of Qinghai nephrite in different colors, which provide a scientific basis for the study of ore-forming environments and conditions of Qinghai nephrites in different colors.

Keywords

• nephrite
• color
• tremolite
• blastic texture
• crystallinity