广东乳源彩石的矿物学特征及颜色成因研究

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

乳源彩石是具有华丽色彩的一种观赏石。采用偏光显微镜、扫描电子显微镜、电子探针、红外光谱仪以及X射线粉末衍射仪等测试手段对4块乳源彩石标本的显微结构、矿物组成和化学成分等进行测试与分析。结果表明,这些乳源彩石具有变粉砂结构,主要由石英组成(占总体质量分数的90%以上),含少量云母,其它矿物的质量分数低,是一种浅变质的变石英粉砂岩;另外,4块乳源彩石样品的结晶度指数相近,结晶度指数最高的绿色样品推测是由于其含有后期充填的鲕状矿物导致。最后对乳源彩石样品的颜色成因进行了分析与探讨,认为其颜色为次生色,是由次生矿物组合、交代蚀变和氧化程度的不同而形成的。

Ruyuan colour stone is a kind of ornamental stones, which is famous for its gor- geous colours, informative images and delicate quality. It was discovered in Ruyuan Yao au- tonomous county, Shaoguan, Guangdong Province of China with a short history, but has a- chieved a great reputation. The predecessors have already had basic understandings of Ruyuan colour stone, including its structure, genetic type, geological process and radiologi- cal 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 convention- al mineralogical research methods to study its petrological characteristics and chemical com- positions to get a comprehensive understanding. The polarizing microscope, scanning elec- tron microscope, electron microprobe, infrared spectrometer and X-ray powder diffraction spectrometer were used to analyze the microstructures, chemical compositions and mineralcomponents 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 5o/00 of the total） and very few other miner- al 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 sam- ples 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.