Mineralogical Characteristics and Colour Genesis of Ruyuan Colour Stones from Guangdong Province

Ruyuan colour stone is a kind of ornamental stones, which is famous for its gorgeous colours, informative images and delicate quality.It was discovered in Ruyuan Yao autonomous county, Shaoguan, Guangdong Province of China with a short history, but has achieved a great reputation.The predecessors have already had basic understandings of Ruyuan colour stone, including its structure, genetic type, geological process and radiological impact.However, the specific cognitions of Ruyuan colour stone including its mineral components and colour genesis have not been known until now.The author used conventional mineralogical research methods to study its petrological characteristics and chemical compositions to get a comprehensive understanding.The polarizing microscope, scanning electron microscope, electron microprobe, infrared spectrometer and X-ray powder diffraction spectrometer were used to analyze the microstructures, chemical compositions and mineral components of the Ruyuan colour stones.The result shows that Ruyuan colour stones have meta-aleuritic textures, tiny mineral grains and no obvious orientation among the grains.The discovery by using scanning electron microscope of irregular hexagonal quartz shows that the quartz in Ruyuan colour stone has undergone metamorphic recrystallization or at least a kind of low-grade metamorphism.Moreover, there are oolitic minerals in the pores of the quartzs of the green sample, which are considered to fill the sample lately.The result of electron microprobe analysis shows that the yellow sample has rhodochrosite and siderite in its fracture.Four pieces of Ruyuan colour stone samples consist of quartz (account for over 90% of the total), minor mica (account for about 5% of the total) and very few other mineral grains (such as hematite and chlorite), and are epimetamorphic quartz siltstone with blocky bedding and texture.In addition, the crystallinity indexes of quartz in the four samples are similar, and the green sample with the highest metamorphic grade has the highest crystallinity index caused by filling of oolitic mineral lately.And the colour of the stone is secondary which is caused by various secondary mineral assemblages, varying degrees of metasomatism and oxidation.