Influence Factor on Transparency of Gaoshan Stone

Gaoshan stone originates in Fujian Province, China. It is a very important variety in Shoushan stone, a famous Chinese seal stone, which is believed to be primary ore. Gaoshan stone is well received by the Chinese people who love traditional culture. When evaluating its quality, transparency of Gaoshan stone is an important criterion.Gaoshan stone is composed of various clay minerals,mainly dickite,sometimes including kaolinite,nacrite,pyrophyllite or illite.In the past,some researchers have explored the influence factors on transparency of Chinese figure stone.In their research,crystallinity and degree of order of kaolin-group minerals are the most significant influence factors on transparency.With the increasing transparency,the seal stone samples show better crystallinity and degree of order of kaolin-group minerals. In order to study influence factor on transparency of Gaoshan stone further,X-ray powder diffration spectrometer(XRD),enviromental scanning electron microscope(ESEM) and LA-ICP-MS were used to analyze the samples collected from Gaoshan mining area and Shoushan stone market. When magnified 5 000 times or 10 000 times by ESEM,electronic microscope photos show that the particle size of the transparent samples is smaller than the opaque samples as well as the transparent samples are more uniform in dimensions than those from the opaque ones.It is not that the transparent samples have higher crystallinity,but the uniformity CO efficient of particle size plays a more important role.X-ray powder diffraction is an effective means of detecting the degree of order of mineral in samples.Diffraction patterns show that the transparent samples have sharp diffraction peaks and the peaks are clearly separated.Hinckley Index(HI) is used to represent the degree of order of kaolin-group minerals.DHI is used to represent the degree of order of dickite and it can be calculated through the intensity of diffraction peaks.Calculated results show that the HI values of transparent samples are higher than those of the opaque ones.Diffraction patterns of opaque samples show more peaks of impurity minerals,such as nacrite,illite and quartz,which means that the impurity minerals also have a strong impact on transparency. In order to explore the influence of element content,LA-ICP-MS was used to detect the major elements and trace elements in samples.The results show that Al content in transdarent samples is a little higher than opaque samples.In the crystal structure of kaolin-group minerals,A1 can be isomorphically substituted by Mg and Fe.This substitution will cause the reduction of structure ordering,and influence the transparency of samples consequently. At the same time,with the reduction of transparency,the content of trace element Li is significantly increased.This phenomenon may due to the different ore-forming stage.Li is an incompatible element,and it will be concentrated in the melt.Therefore the older samples contain less I.i and the younger ones contain more.