Gemmological Characteristics And Origin Identification Of Emerald In Somewhere In Africa

Emerald is one of the four precious gems in the world.In this paper,gemological features of emerald in a certain place in Africa are studied by using conventional gemmological tests,cathodoluminescence,electron probe and Raman spectroscopy.Combining the research findings of scholars on emeralds in various regions of Africa,the author speculated on the origin of emeralds.Emerald is rich in color,emerald green,yellow-green and blue-green,uneven color distribution,with the development of parallel ribbons.The degree of self-shape of the crystal is low,and the shape is mostly lumpy,round,and flat columnar.It is symbiotic with quartz,biotite-phlogopite,rutile and apatite.Due to the lower content of magnesium and sodium,the refractive index and relative density of emeralds are not high.There are groups of gas-liquid two-phase inclusions and needle-like,quadrangular fluid inclusions in emeralds.The solid inclusions identified by Raman spectroscopy and electron probes are emerald,quartz,magnetite,apatite,rutile and anhydrite.The cathodoluminescence test observed emerald luminescence as red,quartz luminescence as blue-violet,and apatite as bright yellow color.According to the luminescence characteristics of quartz and apatite,it is presumed that the emerald is formed under the conditions of rapid cooling at high temperature and grows in contact with the metamorphic environment and is present in the metasinite deposit in the metamorphic rock.Emerald's chemical composition is characterized by high aluminum,low magnesium,and low sodium.The Al₂O₃content is 16.252 to 18.231 wt.%,the Mg O content is 0.491 to 1.179wt.%,and the Na₂O content is 0.160 to 0.594wt.%.In emerald with a parallel color band(colorless or white-green),the content of Al₂O₃in the green part is low,the content of Al₂O₃in the colorless or white part is high,the content of Cr₂O₃is negatively correlated with the content of Al₂O₃,and the change trend according to the content of oxides.It is speculated that the color band is formed during the periodic change of the component concentration.The bending vibration of type I water in infrared spectrum is stronger than that of type II water,and the antisymmetric vibration of type II water is stronger than that of type I water.The stretching vibrations of type I and type II waters in Raman spectra are at 3606 cm^-1and 3597 cm^-1,respectively.In most emeralds,the vibration intensity of type I water is higher than that of type II water,and in blue-green emerald type II water,The vibration intensity is higher than type I water.Absorption bands or absorption peaks due to Cr³⁺and/or V³⁺,Fe³⁺,and Fe²⁺exist in the UV-Vis absorption spectrum,and Al³⁺in the substitution lattice of Cr³⁺and/or V³⁺makes emerald green,and Fe makes the color of emerald yellow or blue.The samples were compared with the emerald features of Zambia,Zimbabwe,Nigeria,Madagascar and Tanzania,and the samples were estimated to be from the Sumbawanga deposit in Tanzania in terms of metallogenic characteristics,basic gemmological characteristics,internal characteristics and chemical composition characteristics.