Study On The Gemmological And Mineralogical Characteristics Of Nanhong Agate From Baoshan,Yunnan Province

Baoshan Nanhong agate is a kind of red quartzite jade,outputting in Baoshan area of Yunnan province. The color of Baoshan Nanhong agate presenting like glue,is more strong than other types of red agate. Combined with previous research results,through the test of the conventional gemological test,microscopic observation,SEM,CL,EPMA, XRD, and micro Raman spectra analysis,the gemological characteristics of Baoshan Nanhong agate, structure, composition and inclusions were studied, and discussed the causes of its color.The conventional gemological characteristics of Baoshan Nanhong agate are similar to the other quartzite jade. Enlarge observation can see a lot of dense red point-like inclusions. Amygdaloidal structures is developed in the surrounding rock.Four kinds of texture can be seen under the microscope: tiny grains,short fibre,long fibre and macrocrystalline quartz. But the SEM photos show no fibre is found,the other textures except macrocrysatlline are consist of tiny globulites. Surrounding rock is altered basalt with intersertal texture. Chlorite and carbonate minerals are often seen in the periphery of Baoshan Nanhong agate. Baoshan Nanhong agate cathodoluminescence is inert,which inclusions visible faint red glow.Main mineral composition of Baoshan Nanhong agates is α-quartz. In the infrared spectrum,absorption peak splitting performance more obvious. This shows that the internal particle more orderly arrangement. Occurring in the range of 3600~2800cm-1 absorption peak,indicating Baoshan Nanhong agate contains some water. By electron microprobe analysis,Baoshan Nanhong agate contains many trace elements. However,the distribution of trace elements is no law. The diffraction peaks of oxides of iron or moganite are not seen in XRD analysis. Surrounding rock contains quartz, plagioclase, chlorite,calcite,dolomite and hematite. The calculated, crystallinity index of Baoshan Nanhong agate range is 5-6. By Raman analysis, detected the presence of moganite in individual regions.The red point-like inclusions is the main causes of Baoshan Nanhong agate’s color. Dot inclusions are gathered by tiny mineral particles. Some inclusions can have nearly spherical appearance,inclusions gather more closely,the deeper the color. The macro-color of Baoshan Nanhogn agate is proportional to the density of point-like inclusions. By Raman spectroscopic analysis,the point-like inclusions is consist of hematite,goethite and lepidocrocite. Speculated that: Fe colloid formation earlier,then it is oxidized to iron oxyhydroxide,after thermal phase transition,eventually formed the hematite. In absorption spectrum,from 550 nm to 300 nm,exists broad absorption. And the Macro-color darker,the greater the absorption intensity is. Speculated this absorption primarily related to Fe3+. But because the agate contains numerous color-causing elements,such as Mn,Cr,Cu,etc.,peak assignment yet to be detailed research.