Research On Mineralogical Characteristics Of Dahua Stone Of Guangxi

Dahua stone is an ornamental stone,which is produced in Red River Basin. The deposit is located in Yantan Town,Dahua Yao Autonomous Country,Hechi City,Guangxi Zhuang Autonomous Region. Dahua stone is composed by various minerals,with the majority being quartz. In this paper,the gemological and mineralogical characteristics of Dahua stone are being studied,in order to determine its chemical compositions,mineral compositions and structural characteristics,and to further infer the cause of its surface color. It can provide a reasonable basis of Dahua stone’s beautiful colors and diverse shapes in Guangxi stone market.Dahua stone of Guangxi has two major surface colors: yellow and red. Other colors such as black,green and light blue can also appear. Samples are almost opaque,and bedded structure can be observed. It has rounded edges and corners. The refractive index is in the range of 1.53 to 1.56,and the density is between 2.65 to 2.76g/cm3. Dahua stone of Guangxi shows a faint fluorescence under the ultraviolet light.In this paper,methods used on studying Dahua stone of Guangxi include infrared spectroscopy,electron microprobe,X-ray powder diffraction and other methods. Results indicate that the major mineral in Dahua stone is quartz,other minor minerals include feldspar,pyroxene,tremolite,etc. Using hydrochloric acid to dissolve the skin of the stone, results show that it contains iron,ferrous ion and manganese ion. Only one sample which contains carbonate is bubbling when reacted with acid.Observing under a single and orthogonal polarizing microscope,quartz and feldspar in the Dahua stone’s sample sheet mostly shows granular texture,with black carbonaceous argillaceous disseminats in it,while tremolite shows columnar texture and fibrous texture. By observing the surface morphology of the Dahua stone under the scanning electron microscope,quartz and feldspar shows granular texture,they are about 5 to 10μm long;while tremolite shows fibrous texture and columnar texture,fibers are about 8 to 15μm long and about 1μm width,with part of fibers being semi-orientated.Combined with the geological survey,it can be inferred that Dahua stone is protolith silicalite after a volcanic eruption and intrusion,occurred with silification,pyritization and marblization,the fragments are being denuded,and after the sedimentation and the weak metamorphism occurring at a low temperature,it eventually forms the Dahua stone.The stone market in Guangxi is developing steadily nowadays. Dahua stone has a great market prospect,and the pattern of its development and utilization are in transition. However, the study of Dahua stone’s mineralogical characteristics are insufficient. Therefore,it needs more in-depth study and a systemic development.