黑龙江穆棱地区宝石级石榴石的宝石学及谱学特征

对黑龙江穆棱新生代玄武岩产出的宝石级石榴石进行了宝石学常规测试、电子探针测试、拉曼光谱、红外光谱和紫外-可见光谱测试，以获得该区石榴石的宝石学特征和谱学特征。化学成分分析表明，该区石榴石为镁铝榴石，含有Fe，Ca，Mn，Cr，Ti等杂质元素。其平均晶体结构化学式为 (Mn_0.022Ca_0.455, Fe2+_0.720, Mg_1.793)_∑=2.990(Ti_0.003Cr_0.009Fe3+_0.062Al_1.951)_∑=2.025(SiO₄)₃。拉曼光谱分析表明该区石榴石存在混合相，由石榴石桥氧振动引起的拉曼位移峰反映出该特征。镁铝榴石桥氧弯曲振动拉曼位移峰位于560 cm-1(A₁g模)和641 cm-1(E_g+F₂g模)，钙铝榴石和铁铝榴石桥氧弯曲振动E_g+F₂g模形成的拉曼位移峰分别位于507和486 cm-1。官能团区红外光谱显示该区镁铝榴石中不存在分子水，但少数镁铝榴石中存在少量的结构水，它们在3 585，3 566和3 544 cm-1处形成阶梯状的弱小吸收峰。该区镁铝榴石多为褐红色，其颜色由杂质离子Cr3+，Fe3+，Mn2+产生。紫外-可见吸收光谱显示，Fe3+的电子跃迁致570，521和502 nm吸收峰，Mn2+的电子跃迁致460和430 nm吸收峰，Cr3+电子跃迁致690和367 nm吸收峰。

Gemology and Spectra Characterization of Gem Garnet from Muling City, Heilongjiang Province

Cenozoic basalts gem-garnets from Muling City, Heilongjiang Province were studied by using standard gemological methods, electron microprobe, Raman spectroscopy, infrared spectroscopy, and ultraviolet-visible spectroscopy to obtain the gemology and spectra characterization. Chemical composition analysis indicates that the garnets are pyropes with some impurity element Fe, Ca, Mn, Cr, and Ti. The average chemical structure formula of the gem-garnet is (Mn_0.022Ca_0.455, Fe2+_0.720, Mg_1.793)_∑=2.990(Ti_0.003Cr_0.009 Fe3+_0.062 Al_1.951)_∑=2.025(SiO₄)₃. Roman spectrum analysis suggests that there are mixed-phases in the garnet, which can be shown by the Roman shift which is caused by bridging oxygen vibration of garnet. The Roman shifts of bridging oxygen bending vibration of pyrope are at 560 cm-1 (A₁g), and 641 cm-1 (E_g+F₂g), while the Roman shifts of bridging oxygen bending vibration caused by E_g+F₂g of almandine and grossular are at 507 and 486 cm-1. IR functional group area indicates that the pyropes have no molecules water, but seldom pyropes have a little structure water, which forms three stepped weak absorption peaks at 3 585, 3 566 and 3 544 cm-1 respectively. Most pyropes are brown-red, which is caused by electronic transitions of impurity ions Cr3+, Fe3+ and Mn2+. UV-Vis spectra show that absorption peaks caused by electron transition of Fe3+ are at 570, 521 and 502 nm, while absorption peaks caused by electron transition of Mn2+ are at 460 and 430 nm, and absorption peaks caused by electron transition of Cr3+ are at 690 and 367 nm.