The Study On Gemological Characteristics Of Guatemalan Jadeite

With the increasing demand and the continuous mining of jadeite resources,the jadeite of Guatemala occupies an increasingly important position,but there are few gemological studies.This paper studies gemmological and mineralogical characteristics of Guatemala jadeite,and provides some basic information for its development and utilization.The jadeite deposit in Guatemala is located on both sides of the Motagua fault,and the local jadeite conforms to the Gemological Characteristics of jadeite,the test results of radioactive elements are smaller than the national standard,and there is no radioactive hazard.Its texture is mainly fine grain-microcrystal texture,and often superimposed late stage texture.It is speculated that the formation and evolution of Guatemalan jadeite can be divided into the following stages.In the first stage,the jadeite is transformed into a crystalloblastic structure.In the second stage,jadeite is generally subjected to brittleness to form cataclastic structure,and metasomatism occurs in the third stage.A part of jadeite is affected by toughness in the second stage,metasomatism and dynamic recrystallization in the third stage.In Guatemala jadeite,the main minerals are jadeite and omphacite.It also includes a small amount of albite,dolomite,graphite,titanite,zircon and so on.In addition,it is confirmed that liquid phase CH₄was contained in the fluid inclusion of Guatemalan jadeite with high desity and internal pressure.It is speculated that liquid C₆H₆may exist in the same inclusion composed mainly of CH₄.It is speculated that the three-phase fluid inclusions contain liquid phase H₂O.The metasomatism channels and metasomatism phenomena in jadeite and chloroprene crystals can be seen in the BSE image,indicating that metasomatism plays an important role in the formation and evolution of Guatemalan jadeite.There are many stages of jadeite and omphacite.In the early stage,the rhythmic bands appeared on the outer surface of the jadeite crystal were formed by the periodic change of Na and Ca,and some bands with high Ca content but low Na content formed omphacite.In the late stage,omphroxene cut jadeite crystals or forming diabase veins,so the temperature in the late stage was higher than that in the early stage.The Cr-rich hydrothermal solution has metasomatism effect on the crystal particles,so that the Cr content of the crystal is increased.In addition,the hydrothermal solution also led to the decrease of Na and Al components and the increase of Fe,Ca and Mg components.The content of trace elements in Guatemalan jadeite is generally less,REE presents a right-leaning trend,U?Zr and Hf are obviously enriched,but the ratio of Zr/Hf is low.As a whole,it is similar to the jadeite in myanmar,which indicates that the jadeite in the two places may have similar genesis or undergo similar metamorphism.The emerald color of Guatemala is caused by the d-d orbital electron transition of Fe and Cr³⁺;Fe causes the visible light absorption spectral line of 437nm,forming blue-green.Cr³⁺causes 691nm absorption band,forming green.Similarly,the absorption band of 638nm and 658nm also caused by Cr³⁺are not visible,which is speculated to be caused by the lack of Cr.