赞比亚、坦桑尼亚和澳大利亚紫红-棕红色石榴石的成分和光谱学对比

紫红-棕红色石榴石是最常见的石榴石品种，其产地来源较多，不同产地因色调和净度不同，价格差异较大，具有产地鉴别的意义。针对坦桑尼亚，澳大利亚，以及新近发现的产地--赞比亚Magodi地区三个产地的样品进行了化学成分和光谱学特征的测试和对比研究。通过激光剥蚀电感耦合等离子体质谱技术（LA-ICP-MS）进行主微量成分分析，发现三个产地的石榴石均为镁铝-铁铝榴石系列矿物。对17种化学成分进行线性判别分析(LDA)，能以96.7%交叉检验准确率对三个产地进行区分。根据标准化典则判别函数的系数，发现MgO，FeO，MnO，Co和Sc等成分对于判别的贡献较大。根据稀土元素配分曲线，发现澳大利亚石榴石在重稀土元素上呈明显上升趋势，计算各样品的重稀土元素和轻稀土元素总含量的比值，澳大利亚为191-334，坦桑尼亚为50-164，赞比亚为9-175。通过拉曼光谱测试，发现随着Mg含量的增加和Fe含量的减少，与Si-O键伸缩振动、Si-O键弯曲振动和硅氧四面体转动有关的拉曼峰向高波数偏移，偏移量与Mg、Fe含量线性相关，澳大利亚样品拉曼峰位整体偏向低波数。三个产地的石榴石在色调上有一定区别，紫外-可见吸收光谱发现这种区别来自于425nm处吸收强度的不同。此外发现，368和503 nm处吸光度的比值具有明显的产地差异，澳大利亚的比值大于1.3，赞比亚介于0.8和1.3之间，坦桑尼亚小于0.8。

Comparison of Chemical Composition and Spectroscopy of Purple-Brownish Red Garnet From Zambia,Tanzania and Australia

Purple-brownish red garnet is the best-selling garnet variety,that from different origins often have various prices owing to particular hues and clarity,so it is necessary to determine the origins.Tanzania and Australia are two main provenances of purple-brownish red garnets,while Magodi,Zambia,is a newly discovered locality.We compared the chemical composition and spectroscopic characteristics of samples from these localities.LA-ICP-MS testing shows that all samples belong to the pyrope-almandine series.The linear discriminant analysis based on 17 chemical components can distinguish different localities with 96.7%cross-validation accuracy.MgO,FeO,MnO,Co,etc.,have larger weights in discrimination than other components based on standardized canonical discriminant function coefficients.According to the distribution curve of rare earth elements,Australian garnets perform an obvious upward trend in heavy rare earth elements.The ratio between the total content of heavy rare earth elements and light rare earth elements was various among localities,9-175 in Zambia,50-164 in Tanzania and 191-334 in Australia.With the increase of MgO and the decrease of FeO,Raman peaks related to Si-O stretching vibration,Si—O bending vibration andSiO₄]rotation shift to the direction of high wavenumber.The offset of wavenumber is linearly correlated to the content of Mg and Fe.Thus,the Australian samples can be roughly distinguished by Raman peaks due to lower MgO content.Garnets from three origins also have a difference in hue.Ultraviolet-visible absorption spectra show that the hues are mainly affected by the absorption strength at 425 nm.The ratio between the absorbance at 368 and 503 nm can be used to distinguish three localities,of which Australia is more significant than 1.3,Zambia is between 0.8 and 1.3,and Tanzania is less than 0.8.