Study On Gemmological Characteristics And Colour Grading Of Nan Hong Agate

Nanhong agate is a red onyx aphanitic quartz jade, compared with ordinary onyx, rich color, strong sense of gum. Nanhong agates on the market currently are the main origin of Baoshan in Yunnan and Sichuan Liangshan areas. Combined with previous studies by conventional gemological tests, microscopic observation(microscopy and SEM), infrared spectroscopy, Raman spectroscopy, electron microprobe, X-ray powder diffraction, magnetic susceptibility test analysis tools to comprehensive study of comparative and quantitative analysis of its color.Gemological characteristics of conventional and Baoshan, Yunnan, Sichuan Liangshan nanhong agate and quartzite ordinary aphanitic similar, except that the magnified observation can see a large number of red dots are densely distributed inclusions, commonly known as "cinnabar point." Although the "African " red agate also have this feature point, but compared with the nanhong agate, and the lack of rich colors and special sense of gum.Nanhong agate and fluorescence under ultraviolet cathodoluminescence showed inert, polarizing microscope nanhong agate common fine particulate-short fiber- long radial structure composed of fibrous, often repetitive and appear law, the use of SEM observation, find information fine granular crystal ine quartz, the rest by the micron level aggregate to form pellets, and the gap between the pellets common. Electron microprobe, IR and Raman spectroscopy shows the main mineral nanhong agate of α- quartz containing hematite, oblique silica, calcite and the like. IR spectrum 2800cm-1 ~ 3600 cm-1 absorption peak appearing in the range seen in the aqueous agate further by differential thermal analysis agate that the water content from about 1% to 2% by weight loss. Red dot of color caused by a large number of approximate hexagonal inclusions component analysis showed mainly composed of hematite composition. The more dense red inclusions, macroscopic sample darker. X-ray powder diffraction analysis nanhong agate quartz crystal inity4-6, lower than the average onyx degree of crystallinityBaoshan agate lightness L * range of 35-45, mostly concentrated in 40 other regions basically no. Sichuan Liangshan agate lightness L * of between 40-60, mostly concentrated in 50 other districts less distributed. Sichuan Liangshan whole agate agate agate lightness higher than the Baoshan area. Baoshan agate saturation C * range of 25-35, mostly concentrated in 30 other regions substantially less visually observed partial orange. Sichuan Liangshan agate saturation C * is between 30-50, widely distributed, covering almost all areas Baoshan saturation C *.