光谱学与光谱分析, 2019, 39 (2): 543, 网络出版: 2019-03-06  

福建寿山溪蛋石的矿物学和谱学研究

Mineralogical and Spectroscopic Study on Xidan Stone from Shoushan County, Fujian Province
作者单位
中国地质大学珠宝学院, 湖北 武汉 430074
摘要
溪蛋石是寿山石的著名品种之一, 指散落在月洋溪中的一种山坑石, 系寿山石中的芙蓉石品种的风化产物。 残块经过雨水冲刷流入溪中, 复受水流、 河沙等长年冲击, 形成浑圆卵石状外表, 因其易于雕刻塑形, 广受近代雕刻家好评。 为了探究寿山溪蛋石的矿物学和谱学特征, 运用常规的宝石学测试方法、 X射线粉末衍射仪、 傅里叶变换红外光谱仪、 显微激光拉曼光谱仪和电子探针等测试方法, 对几件黄色溪蛋石样品的矿物组成、 红外及拉曼光谱特征、 化学成分等展开了全面研究。 常规宝石学测试结果表明, 溪蛋石样品的相对密度约为2.8, 摩式硬度小于3; 为了避免层状硅酸盐矿物的择优取向性, XRD实验采用侧压法, 测试结果表明, 溪蛋石由较纯的叶蜡石组成, 并以单斜晶系(2M型) 叶蜡石的形式存在, 以2θ=19°~22°之间4.44 (020) , 4.24 (112) 和4.17 (111) 三个衍射峰为特征, 其中(112) 和(111) 两个衍射峰相距很近, 在(112) 衍射峰(2θ=21.06°) 右侧出现了一个衍射肩; 在2θ=28°~31°之间, 以3.06 (003) 强峰(2θ=29.05°) 为特征; 采用红外光谱仪可以有效的确定溪蛋石基质和石皮部分的矿物成分。 样品的红外光谱表明, 溪蛋石的风化皮与基质部分矿物成分均为叶蜡石, 指纹区的主要特征峰为1 122, 1 068, 1 052, 949, 853, 835, 812, 541和484 cm-1, 其中, 1 122 cm-1归属于Si—O伸缩振动, 1 068和1 052 cm-1附近强而尖锐的吸收峰由简并解除的Si—O—Si伸缩振动引起, 949 cm-1左右的吸收窄带由Al—OH面内弯曲振动引起; 853, 835及812 cm-1处强度较弱的倒“山”字形吸收谱带属于Al—OH面外弯曲振动, 541 cm-1处吸收峰为Si—O—Al伸缩振动引起, 484 cm-1归属于Si—O弯曲振动; 官能团区3 675 cm-1处尖锐的吸收峰由Al—OH伸缩振动所导致, 指示了叶蜡石结构的高度有序化。 采用显微激光拉曼光谱对溪蛋石中的包裹体进行测试, 以确认其矿物成分。 结果显示, 点片状黑色包裹体为赤铁矿, 拉曼特征峰为224, 291, 409, 494以及1 315 cm-1, 灰白色矿物为硬水铝石, 拉曼特征峰出现在448, 499和667 cm-1, 还存在707, 788和1 194 cm-1处弱峰, 与硬水铝石的标准谱峰吻合。 此外, 基质部分在111, 194和261 cm-1处的拉曼峰由Si—O键伸缩振动所致, 706 cm-1处强而尖锐的拉曼峰以及3 670 cm-1处的峰是由O—H伸缩振动所致, 与叶蜡石的拉曼光谱一致, 也与红外光谱的测试结果对应。 根据矿物单位分子中的电价平衡原则和正电荷总数, 利用电子探针测试数据计算溪蛋石的平均晶体结构化学式为: (Al1.98Na0.02Cr0.01)[(Si3.98Al0.02)O10](OH)2。 溪蛋石化学成分稳定, 主要含有Si(64.88%) , Al(27.55%) 。 寿山溪蛋石中含0.2%左右的Cr和0.02%左右的Fe和Cr元素含量远大于Fe元素, 因此推测溪蛋石的浅黄色由Cr和Fe离子共同作用所致。
Abstract
Xidan Stone, which is a kind of mountain stones scattered across the Yueyang Stream and weathering product from the famous Shoushan Furong Stone, is one of the well-known varieties of Shoushan stone. Washed into the stream by rain, blocks of Xidan Stone have been impacted by the water and river sand for several years to form a round pebble appearance. Because it is easy to be sculptured, Xidan Stone is widely praised by modern sculptors. In order to analyze this stone from different aspects including mineral components, spectroscopic features, chemical composition and color origin, the systematic mineralogical and spectroscopic studies were conducted on the yellow Xidan stone samples from Shoushan rivulet of Fujian Province, with the help of standard gemological methods, X-Ray powder diffraction, infrared absorption spectroscopy, laser Raman spectroscopy and Electron probe microanalysis. The gemological testing results inferred that Xidan stone samples are pebble-shaped which contain light yellow substrate and rough weathered skin. Examined under magnification, the Xidan stone samples have tiny black dot-like inclusions and white grey mineral component. The Xidan stone samples have an average relative density of 2.8 by hydrostatic weighing method and a Moh’s hardness below three. According to the testing results of XRD, the major constituent mineral of Xidan stone is pyrophyllite, which is in the type of monoclinic pyrophyllite (2M type). The characteristic feature is the three diffraction peaks of 4.44 4.44  (020), 4.24  (112) and 4.17  (111) between 2θ=19° and 22°. The two diffraction peaks (112) and (111) lie closed to each other, therefore a diffraction shoulder appears on the right side of the (112) diffraction peak (2θ=21.06°). Another characteristic feature is the 3.06  (003) strong peak (2θ=29.05°) between 2θ=28° and 31°. Infrared spectroscopy is an effective method to tell the mineral composition of weathering skin parts as well as the substrate parts of Xidan stone samples. The FTIR spectrum shows that these two parts share the same mineral component of pyrophyllite. In fingerprint region, the main absorption bands are 1 122, 1 068, 1 052, 949, 853, 835, 812, 541 and 484 cm-1. Infrared absorption band at 1 122, 1 068 and 1 052 cm-1 are induced with Si—O symmetric stretching vibration and Si—O—Si antisymmetric stretching vibration. Infrared absorption band at 949 cm-1 is induced with Al-OH in-plane bending vibration. Mountain-like infrared absorption bands at 853, 835 and 812 cm-1 are induced with Al—OH out-of-plane bending vibration. Infrared absorption peaks at 541 and 484 cm-1 are induced with Si—O—Al stretching vibration and Si—O bending vibration. In high frequency region, the acute infrared absorption peak at 3 675 cm-1 is induced with Al—OH stretching vibration indicating the highly ordered structure of Xidan Stone samples. Laser Raman spectroscopy is an effective and non-destructive way to analyze the inclusions. LRM testing confirmed that the black inclusions are composed by hematite and the white grey mineral component is diaspore. Raman peaks at 224, 291, 409, 494 and 1 315 cm-1 are typicalfeatures of hematite. Raman peaks at 448, 499, 667, 707, 788 and 1 194 cm-1 correspond to the typical features of diaspore. In addition, Raman spectrum of substrate parts of samples shows the characteristic peaks of pyrophyllite at 111, 194 and 261 cm-1, which are induced with O—H stretching vibration. Based on the unit price of mineral balance principle molecule and the total number of positive charges, the average crystal structural formula of Xidan Stone is (Al1.98Na0.02Cr0.01)[(Si3.98Al0.02)O10](OH)2. Thedata of EPMA testing tell that Xidan Stone samples have stable chemical composition. Samples mainly contain Si(64.88%) and Al(27.55%). Given that the Xidan Stone samples contain fewer Fe(0.02%) but more Cr(0.2%), Fe as well as Crmightcause the light yellow of stream-egg stones.
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许雅婷, 秦涵斐, 陈涛. 福建寿山溪蛋石的矿物学和谱学研究[J]. 光谱学与光谱分析, 2019, 39(2): 543. XU Ya-ting, QIN Han-fei, CHEN Tao. Mineralogical and Spectroscopic Study on Xidan Stone from Shoushan County, Fujian Province[J]. Spectroscopy and Spectral Analysis, 2019, 39(2): 543.

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