Phase composition and genesis of pyroxenic jadeite from Guatemala: insights from cathodoluminescence

Abstract

Guatemalan jadeite has a long history, and much Guatemalan jadeite can be found on the market today with a variety of colors and species diversity. Seven varieties of green pyroxenic jadeite from Guatemala with greyish green, yellow green, brilliant green, blue green, dark green, black green and mottled green colors were investigated by combining the methods of XRD, Raman spectroscopy, cathodoluminescence, EPMA and μ-XRF mapping. The results showed that according to the composition, Guatemalan pyroxenic jadeite can be divided into three categories: jadeite jade, omphacite jade, and jadeite–omphacite jade. According to the characteristics of cathodoluminescence, it can be speculated that the formation of jadeite undergoes three stages, and the formation of jadeite jade is mainly due to the crystallization (Jad I) of the early jadeite fluid, along with the second-stage fluid metasomatism/crystallization (Jad II). In the later stage, the fluid that is rich in Ca–Mg–Fe components can replace early Jad I/Jad II, or it can coexist with Jad II, and metamorphism occurs to produce omphacite jade. The jadeite–omphacite jade can be formed when the omphacite fluid with incomplete metasomatism, with uneven texture and reduced transparency.