The Study On Gemology And Mineralogy Of Southern-Red Agate In Baoshan County, Yunnan Province

Southern-red Agate, from the southwest of China, is the natural red jade. Because of its nice quality and bright color, people love it very much. This essay, by combining the research results of the former talents, makes a systematic and detailed research on the gemological characteristic, mineral components, structural features and cause of color of Southern-red Agate in Baoshan County, Yunnan Province, Liangshan County, Sichuan Province and Africa, experiments including observation under microscope, XRD, XRF,infrared spectra, RAMAN, EMPA, UV-visible spectral. Moreover, it makes an intensive analysis on the aspects including the differences and relations among the Southern-red Agate of different deposits. Also, combined with the market situation, it discusses the quality evaluation and the classification system of Southern-red Agate.The result of the observation test shows that Southern-red Agate can be light red, red and crimson. They are lipidic-glassy luster, sub-translucent-translucent and are often fracture development. Their indexes of refraction are 1.54, with a relative density from 2.62 to 2.65 and hardness from 6 to 7. Many red particles can be observed in the color of transparent-semitransparent samples by magnification, and it can’t be observed in the red and sub-translucent Southern-red Agate samples.Southern-red Agate has three kinds of structure: cryptocrystalline structure, fibrous structure and radiated fibrous structure. It appears straight dividing line at the intersection of the radiated fibrous structure in different directions and the turn of the circular texture.Quartz grains have different orientation at both sides of the dividing line. This straight dividing line may be the cause of fracture development in Southern-red Agate.Infrared spectra and XRD indicate that the main mineral of Southern-red Agate is quartz. In addition to Si and O elements, Southern-red Agate also contains small amounts of Fe, according to XRF. Moreover, it can be seen that the bright degree of red part is directly proportional to the content of Fe. RAMAN points that a part of fissures of Southern-red Agate in Baoshan County have been filled with late calcite, and the minerals of the red particles are hematite. Hematite are hexagonal in size of 2-20μm in Southern-red Agate in Baoshan County, while the hematite in Southern-red Agate in Liangshan County are round in size of only 1μm.EPMA analysis results indicate that ferruginous component in the red particles of Southern-red Agate in Baoshan County, which is distributed on the edge of the red particles,is more dispersive than Southern-red Agate in Liangshan County. The syngenetic and epigenetic calcites which are included in Southern-red Agate in Baoshan County prove the environment of the formation and after is rich of Ca CO3, and the KCl grains that are found in Southern-red Agate in Liangshan County prove the environment of the formation is rich of potash. Besides, the amount of maganese in Southern-red Agate in Liangshan County is more than Southern-red Agate in Baoshan County, which could be the reason for Southern-red Agate in Liangshan County being crimson.UV-visible absorption spectrum indicates that sub-translucent Southern-red Agate can absorb any light in bluish violet range and let all light transmit through the range of red and orange, while transparent and semitransparent Southern-red Agate can absorb any light in blue range and let all light transmit through the range of violet, red and orange. The hue,saturation and value in Southern-red Agate can be quantitative representation by color measurement, which could provide the basis for the quality evaluation in Southern-red Agate.The comparison shows that the characteristics of Southern-red Agate from different deposits are similar and hard to classify. The quality evaluation of Southern-red Agate can be considered from seven aspects including color, transparence, luster, clarity, cranny, size and craftwork. According to the standard of quality evaluation, Southern-red Agate can be divided into four grades.