安徽殿庵山绿松石的宝石学特征研究

Study on Gemmological Characteristics of Turquoise from Dian'anshan,Anhui Province

安徽省殿庵山地区绿松石属于新近发现的小规模开采的玉石资源。采用电子探针、扫描电子显微镜、傅里叶变换红外光谱仪、紫外-可见光谱仪等测试方法,重点就该地区绿松石的化学成分、矿物组成、微结构、红外吸收光谱、紫外-可见吸收光谱等特征进行综合对比研究。结果表明,该地区绿松石的化学成分以贫Si、相对富Fe为特征,随着FeOT/CuO比值的递增,绿松石色调由蓝逐渐变绿。该类绿松石以结核状、细脉状产出,主要为微晶和鳞片状结构,部分为放射纤维状结构、团粒状结构及皮壳状结构。该类绿松石孔洞内微晶普遍发育,主要以毛发状、微针状、短柱状及板片状相互交织结晶生长,殿庵山绿松石整体显示风化淋滤型矿床所特有的特征。笔者对绿松石的颜色成因及矿床成因进行初步探讨。

Currently turquoises have been discovered in the mining areas of Dian^anshan,An- hui Province. Turquoise samples from Dian＇anshan were analyzed by using electron micro- probe （EMPA）, polarizing microscope, scanning electron microscope （SEM）, Fourier trans- form infrared spectrometer （FTIR） and ultraviolet-visible spectrometer （UV-Vis）. The chemical compositions, mineral components and microstructure of the turquoises were also studied in this paper. The turquoise mines from Dian^anshan are located in a mountainous region of Ma＇anshan,Anhui Province, where geological formation activities are abundant. The turquoises are found as concretion form and vein within the cracks of dioritic pophyrite and compressocrushed zone. The structure of turquoises is compact in deeper area. Near the earth＇s sur- face, they are in the form of fine vein and thin film with loose texture. The colour of the tur- quoise are from blue to green. The electron microprobe analysis indicates that the chemical compositions of blue turquoises from Dian＇ anshan deviate from theoretical value. The w（Al2O3 ） varies between 37.47% and 38.31%,w（P2O5） between 34. 92% and 35.81%, and w（CuO） between 7.84% and 9.10%, while the green turquoise cantains less contents of Al2O3 and CuO. The blue turquoise cantains about 2.0% FeOT and the green turquoise cantains 9.40% FeOT. The colour of turquoise is gradually from blue to green with the increase of rate of FeOT/CuO. Compared to the other turquoise mines in China, the turquoise from Dian＇anshan is charac- terized by poor Si and rich Fe. The polarizing microscope investigations show that the turquoises from Dian＇anshan are microcrystal and scales structures, some of which are radial fiber, granular and crust structures. The turquoise crystals tend to be radial growth. The crust structure shows that the turquoise deposits from Dian＇anshan are of weathering-leaching characteristics. The SEM results show that the turquoise crystals are mainly leaf shape in form of tight pile. The turquoise crystal growth is like micro-hole, short columnar and plate structure, which tends to radial spherolitic structure. The infrared spectrum bands of the turquoises are caused by vibration of constitution water, crystal water and phosphate group. The stretching vibrations of constitution water are recorded at 3 510, 3 464 cm-1 with a sharp band. The stretching vibrations of crystal water are recorded at 3 294, 3 080 cm-1 with a moderate band. In addition, weak bands at 837, 788 cm-1 are caused by the bending vibration of constitution water and crystal water. Three bands assigned to the stretching vibrations of phosphate group are approximately recorded at 1 108, 1 191 and 1 056 cm-1. Three bands assigned to the bending vibrations of phosphate group are approximately recorded at 650, 570 and 484 cm 1. The UV-Vis spectra of the turquoise samples are different. A strong and narrow centered at 430 nm is caused by Fea＋ d--d electronic transition, and a broad absorption centered at 676 nm is caused by Cu2＋ d--d electronic transition in all samples. Howev band centered at 852 nm in the green turquoise sample is caused by Fe2＋ d--d electronic transition. The band appearing at 776 nm in the blue turquoise sample may be caused by the mixture effect of Cu and Fe cation.