Nanhong agate is widely welcomed in China because of its bright red colour.The pursuit of the red agate is the inheritance of Chinese red agate culture,which can be dated back to more than 3000 years ago.Field survey ...Nanhong agate is widely welcomed in China because of its bright red colour.The pursuit of the red agate is the inheritance of Chinese red agate culture,which can be dated back to more than 3000 years ago.Field survey showed Nanhong agate geographically distributed in Yunnan and Sichuan provinces,the Southwestern of China(Fig.1).Geologically,Nanhong agate can be either produced as fillers in cracks and pores of the Late Permian E’meishan basalts,or as pebbles in the Early Triassic conglomerates and mudstones.Petrographic analyses reveal the formation of agates could be linked to the alteration of basalts by the silicon releasing in the process of transformation from pyroxene to chlorite.The formation of Nanhong agates could have experienced multi-stage alterations and crystallizations,which are supported by the occurrence of multi-stage chlorites and different homogenization temperatures of fluid inclusions bearing in the coarse grained quartz.The Nanhong agates are characterized by diffusely distributed hematite and/or goethite,causing the red to reddish orange in colour.These iron oxides occurre as aggregates showing dominantly spherical shapes and minor visible ellipsoid,hemisphere,radial and veil shape,with a size generally between 1.20μm and 43.21μm.Raman spectra,scanning electron microscopy,and high resolution transmission electron microscopy confirmed the present of hematite with single hematite particles smaller than 100 nm.Wide market survey of the selling Nanhong agates presented the quantified colour parameters,including hue,saturation,and brightness,obeying normal distribution in the Hue-Saturation-Brightness(HSB)colour space.After standardization,the hue(H)of Nanhong agate is mainly distributed in a range between[3.20°,17.52°]at a 95%confidence level.The saturation(S)and brightness(B)are mainly within[63.82%,92.69%]and[42.97%,75.37%],respectively.The Nanhong agates could be statistically classified as different grades by the Two Step Cluster analysis,which is objective compared to subjective visual evaluation.Factors causing the colour difference of Nanhong agates are attributed to the colour properties and distribution characteristics of hematite and goethite.The hue of Nanhong agate is dependent on the colour of the impurity minerals,hematite or goethite.Saturation is affected by the area ratio of impurity minerals.As the area ratio of impurity minerals is both affected by the distribution density and the average particle size,the saturation of Nanhong agate is the largest when the average particle size is near 10μm.No obvious correlation is observed between the brightness of Nanhong agates and their related properties and characteristics.展开更多
Jadeite jade,also called Feicui in China,is the most popular jade variety and one of the best selling gems in China.Colour and transparency are the primary quality factors that determine the value of Feicui.Jadeite ja...Jadeite jade,also called Feicui in China,is the most popular jade variety and one of the best selling gems in China.Colour and transparency are the primary quality factors that determine the value of Feicui.Jadeite jade is a polycrystalline aggregate,primarily consisting of jadeite(NaAlSi2O6) and including accessory minerals such as omphacite,albite,amphibole,and chromite[1-2].Gem-quality Feicui material is only found in a few countries,namely Myanmar,Guatemala,Russia,Kazakhstan,and Japan[3-5].Myanmar is the traditional and most important producer of gem-quality jadeite jade,while Guatemala has become the second-largest producer[6]. "Ice jade" is a translucent variety of jadeite jade(also known as Feicui) that is generally of high value.Reportedly from the Morales mine in the Izabal Department of Guatemala,it has recently appeared in the Chinese jewelry market.In this study,the structural characteristics,mineral compositions,and colour genesis of Guatemalan "ice jade" were studied using UV-Vis-NIR and Raman spectroscopy,X-ray diffraction,electron probe microanalysis,scanning electron microscopy,and cathodoluminescence. "Ice jade" from the Morales mine in Guatemala is composed of almost pure jadeite,containing very small amounts of accessory minerals,including omphacite and albite.The omphacite grains are often nearly colourless and not easily observed,while the albite grains cluster as white snowflake-like inclusions or dispersed as small specks.The "ice jade" exhibits a fine-grained structure,occasionally coexisting with a micro-granular structure.The relatively pure chemical compositions of sodium pyroxene accompany with a fine texture produced a transparent to semi-transparent and near-colourless appearance.A small amount of dispersed fine-grained omphacite is considered the cause of the pale green colour in "ice jade" from Guatemala.The Guatemalan origin can be determined from its characteristic appearance,microstructure,accessory minerals,and chemical compositions.展开更多
文摘Nanhong agate is widely welcomed in China because of its bright red colour.The pursuit of the red agate is the inheritance of Chinese red agate culture,which can be dated back to more than 3000 years ago.Field survey showed Nanhong agate geographically distributed in Yunnan and Sichuan provinces,the Southwestern of China(Fig.1).Geologically,Nanhong agate can be either produced as fillers in cracks and pores of the Late Permian E’meishan basalts,or as pebbles in the Early Triassic conglomerates and mudstones.Petrographic analyses reveal the formation of agates could be linked to the alteration of basalts by the silicon releasing in the process of transformation from pyroxene to chlorite.The formation of Nanhong agates could have experienced multi-stage alterations and crystallizations,which are supported by the occurrence of multi-stage chlorites and different homogenization temperatures of fluid inclusions bearing in the coarse grained quartz.The Nanhong agates are characterized by diffusely distributed hematite and/or goethite,causing the red to reddish orange in colour.These iron oxides occurre as aggregates showing dominantly spherical shapes and minor visible ellipsoid,hemisphere,radial and veil shape,with a size generally between 1.20μm and 43.21μm.Raman spectra,scanning electron microscopy,and high resolution transmission electron microscopy confirmed the present of hematite with single hematite particles smaller than 100 nm.Wide market survey of the selling Nanhong agates presented the quantified colour parameters,including hue,saturation,and brightness,obeying normal distribution in the Hue-Saturation-Brightness(HSB)colour space.After standardization,the hue(H)of Nanhong agate is mainly distributed in a range between[3.20°,17.52°]at a 95%confidence level.The saturation(S)and brightness(B)are mainly within[63.82%,92.69%]and[42.97%,75.37%],respectively.The Nanhong agates could be statistically classified as different grades by the Two Step Cluster analysis,which is objective compared to subjective visual evaluation.Factors causing the colour difference of Nanhong agates are attributed to the colour properties and distribution characteristics of hematite and goethite.The hue of Nanhong agate is dependent on the colour of the impurity minerals,hematite or goethite.Saturation is affected by the area ratio of impurity minerals.As the area ratio of impurity minerals is both affected by the distribution density and the average particle size,the saturation of Nanhong agate is the largest when the average particle size is near 10μm.No obvious correlation is observed between the brightness of Nanhong agates and their related properties and characteristics.
文摘Jadeite jade,also called Feicui in China,is the most popular jade variety and one of the best selling gems in China.Colour and transparency are the primary quality factors that determine the value of Feicui.Jadeite jade is a polycrystalline aggregate,primarily consisting of jadeite(NaAlSi2O6) and including accessory minerals such as omphacite,albite,amphibole,and chromite[1-2].Gem-quality Feicui material is only found in a few countries,namely Myanmar,Guatemala,Russia,Kazakhstan,and Japan[3-5].Myanmar is the traditional and most important producer of gem-quality jadeite jade,while Guatemala has become the second-largest producer[6]. "Ice jade" is a translucent variety of jadeite jade(also known as Feicui) that is generally of high value.Reportedly from the Morales mine in the Izabal Department of Guatemala,it has recently appeared in the Chinese jewelry market.In this study,the structural characteristics,mineral compositions,and colour genesis of Guatemalan "ice jade" were studied using UV-Vis-NIR and Raman spectroscopy,X-ray diffraction,electron probe microanalysis,scanning electron microscopy,and cathodoluminescence. "Ice jade" from the Morales mine in Guatemala is composed of almost pure jadeite,containing very small amounts of accessory minerals,including omphacite and albite.The omphacite grains are often nearly colourless and not easily observed,while the albite grains cluster as white snowflake-like inclusions or dispersed as small specks.The "ice jade" exhibits a fine-grained structure,occasionally coexisting with a micro-granular structure.The relatively pure chemical compositions of sodium pyroxene accompany with a fine texture produced a transparent to semi-transparent and near-colourless appearance.A small amount of dispersed fine-grained omphacite is considered the cause of the pale green colour in "ice jade" from Guatemala.The Guatemalan origin can be determined from its characteristic appearance,microstructure,accessory minerals,and chemical compositions.
