The Structural Characteristics and Chemical Composition of Serpentine Jade Weathering Rinds: Implications for the Formation Process

Abstract

Weathering rind retains the greatest extent of the mineralogical and chemical composition information of the original mineral. Recently, we found some brownish-yellow or khaki serpentine jade weathering rinds with a thickness of 0.2–0.6 cm in Ji’an. The purpose of this paper is to explore differences in structural characteristics and chemical composition between weathering rinds and unweathered cores and summarize the formation of weathering rinds. In terms of structural characteristics, weathering rinds have smaller a0, b0, β values than unweathered cores; the specific surface area is 13.3987 m2/g; the pore volume is 0.0314 cm3/g; and the pore size distribution is characterized as more mesoporous (2–10 nm). The weathering rind shows partial dissolution of serpentine grains, increased porosity, and loosening structure. In terms of chemical composition, the weathering rind is characterized by the decrease of some serpentine major elements (Si, Mg, and Fe) and the increase of some impurity elements (Al, Ca, K, Na, and Cl). The weathering rind is the result of further alteration of serpentine jade, accompanied by the reduction of the Fe3+/Fe2+ ratio and the generation of the clay mineral (chlorite). In addition, it was also found that Ji’an serpentine jade belongs to Mg-bearing carbonate rock genesis, which are derived from marine deposits.