Study On Gemmological Mineralogy And Quality Evaluation Of High-Grade Green Jadeite Jade From Guatemala

In recent years,Guatemala has become the second largest jadeite Jade origin.Following the impact of the new coronavirus pneumonia epidemic and the civil strife in Myanmar in 2020,Myanmar’s jade raw materials basically cannot enter China’s mainland,and the Ruili market is almost paralyzed.In recent years,Guatemala high color material enters our country,it quickly occupied the market,Guatemalan high-grade green jadeite Jade in the main wholesale market transactions accounted for more than 40%of high-end color.Consumers can not correctly distinguish between Myanmar Feicui and Guatemala Feicui,especially for the high-grade green jadeite Jade,even the insiders can not be correctly distinguished them!From the perspective of material value,Guatemalan high-grade green jadeite Jade has the advantages of large quantity and low price.Its appearance in the market is bound to have a certain impact on the stability of pricing and value of Myanmar high-grade green jadeite Jade market.In this paper,through the observation of internal and external characteristics,microstructure observation,gemological constant test（relative density,hardness,refractive index value,fluorescence,etc.）and modern test technology analysis（infrared spectrum analysis,laser Raman spectrum analysis,electron probe analysis,ultraviolet-visible absorption spectrum analysis）of Guatemalanhigh-grade green jadeite Jade,the mineral composition,chemical composition and structural structure of Guatemalanhigh-grade green jadeite Jade are discussed,the coloration mechanism is studied,the indicativecharacteristics of its origin are revealed,and the quality evaluation of Guatemalan high-grade green jadeite Jade is made,which is conducive to the identification and trade of Guatemalanhigh-grade green jadeite Jade in the market.Guatemalan high-grade green jadeite Jade,showing bright green,or superimposed with a certain degree of gray to blue to green,is pan-grease luster in glass luster,refractive index value of 1.66（point measurement）,optical characteristics of heterogeneous aggregates;fluorescence is inert under UV light.Strong absorption lines at 437 nm and690 nm can be seen in the spectrometer.Mohs hardness is about 7,relative density is3.32-3.39;local visible aggregate particles in the’green’,containing more white cotton,black irregular inclusions.The structures mainly include semi-self-shaped-self-shaped columnar structure,metasomatic structure,mylonitic structure and super-mylonitic structure,filling structure,mottled structure and banded structure.The main minerals of Guatemalan high-grade green jadeite Jade are jadeite and omphacite,and the secondary minerals contain a small amount of albite,sphene,phlogopite,clinozoisite,chalcocite,molybdenite and arsenic nickel ore.The white cotton agglomerate inclusions are a combination of silicate crystalline phase jadeite,sphene and fluid phase dominated by CO₂and CO.The black irregular inclusions are carbonaceous inclusions and do not crystallize into graphite,which are amorphous carbon.The high pigment jadeite from Guatemala is colored by Cr³⁺and Fe³⁺ions.The absorption lines at 630,660 and 690 nm of omphacite jadeite samples from Guatemala are stronger than those of jadeite samples from Myanmar,which is due to the high content of Cr³⁺ions.According to the mineral composition and its evolution,the mineralization is divided into three stages:（1）the early mineralization products are jadeite with coarse-grained,semi-automorphic-automorphic columnar structure,and the chemical composition is very pure;（2）The main ore-forming period is dominated by metasomatism.The products formed in the early stage are fine particles of jadeite,which contain relatively high contents of Fe O,Cr₂O₃,Mg O and Ca O compared with the jadeite in the first stage.The products formed in the late stage are fine particles of omphacite,which have high contents of Mg O and Ca O,and show different shades of green due to the regular change of Cr₂O₃content.（3）The products of late mineralization are jadeite（or albite）+titanite,etc.,with filling structure.Titanite is distributed in the form of net veins between jadeite and omphacite particles or in micro-fractures.The late jadeite（albite）+sphene+fluid inclusion combination,that is,the white cotton in jadeite,is actually a kind of fluid melt inclusion.The fluid phase in the fluid melt inclusions contains CO₂,CO and other components,of which the characteristic Raman shift peak at 2145cm^-1is the strongest,indicating a strong reduction mineralization environment with high CO content,which is consistent with the widespread presence of amorphous carbon in the sample.The results show that except for a few samples with grayish green color,the mineral composition is mainly omphacite.Most of the Guatemalan high-grade green jadeite samples studied are mainly jadeite or jadeite is one of its main mineral components.The combination of’late jadeite+reticulate sphene+CO-based fluid inclusions’commonly found in white cottony minerals can be used as an important reference for the identification of high-grade green jadeite from Guatemala and Myanmar.Guatemala high-color jade quality evaluation:from the color’color’,transparency’water’,purity’flaw’,texture’species’,process’work’,and mosaic effect’gold’six aspects of its objective evaluation,namely the six elements of quality evaluation.