广西黑青色阳起石玉振动光谱特征研究

选取产自广西大化瑶族自治县岩滩镇的黑青色阳起石玉为研究对象，采用电子探针、傅里叶变换红外光谱仪和激光拉曼光谱仪就其化学成分和振动光谱特征进行测试分析，并对小半径金属阳离子在阳起石晶体结构中的占位情况予以讨论。结果表明，广西黑青色阳起石玉的主要矿物组成为富铁阳起石，并含有少量铁阳起石；化学成分中的高含量FeO_T(Wt%：18.596%~26.791%)是导致其折射率值(1.64)、密度值(3.12 g·cm-3)偏高且在自然光下呈黑色、透射光下呈绿色的主要原因。受晶体结构中Fe2+对Mg2+的类质同象替代作用影响，广西黑青色阳起石玉1 400~400 cm-1范围内的红外吸收谱带与100~1 200 cm-1范围内的拉曼谱峰位置较透闪石向低频区发生偏移，频差不等；且中红外、近红外吸收光谱和拉曼光谱中均可见四个(MgMgMg)OH(A带)，(MgMgFe2+)OH(B带)，(MgFe2+Fe2+)OH(C带)和(Fe2+Fe2+Fe2+)OH(D带)振动谱带，其中基频振动谱带分别位于3 674，3 660，3 644和3 625 cm-1附近，倍频振动谱带分别位于7 183，7 154，7 118和7 077 cm-1附近，相对强度为A＜D＜B＜C。化学成分和M-OH红外振动谱带积分面积计算结果显示广西黑青色阳起石玉晶体结构中Mg2+优先占据M₂位置，Fe2+优先占据M₁位置；Mg2+和Fe2+在M₁和M₃位置上的分布相对有序，占位系数接近于1。综合分析认为广西黑青色阳起石玉的变质程度属绿片岩相范畴。

Vibrational Spectral Characteristics of Ensignia Actinolite Jade from Guangxi,China

Chemical composition and vibrational spectral characteristics of ensignia actinolite jade from Guangxi, China were investigated using electron microprobe(EPMA), Fourier transform infrared spectrometer(FT-IR) and laser Raman spectrometer(Raman). The site occupancy situation of metal cations with small ionic radii in the crystal structure of actinolite was discussed as well. The result indicates that ensignia actinolite jade from Guangxi is primarily composed of Fe-rich actinolite and minor ferroactinolite, and the high content of FeO_T(Wt%：18.596%~26.791%)is the main reason for its high refractive index(1.64), density(3.12 g·cm-3) as well as black color in natural light and green color in transmission light. Due to the influence of Mg2+-Fe2+ isomorphous substitution in the crystal structure, the infrared absorption bands in 1 400~400 cm-1 and Raman peaks in 100~1 200 cm-1 all shift towards the low-frequency region with various frequency differences. In addition, four vibration bands(MgMgMg)OH(band A), (MgMgFe2+)OH(band B), (MgFe2+Fe2+)OH(band C), and (Fe2+Fe2+Fe2+)OH(band D)are displayed in mid- and near-infrared spectra as well as Raman spectra, among which the bands related to M-OH fundamental frequency vibrations appear at nearly 3 674, 3 660, 3 644 and 3 625 cm-1, respectively. While the bands related to M-OH multiple frequency vibrations appear at nearly 7 183, 7 154, 7 118 and 7 077 cm-1, respectively, and their relative intensity is A＜D＜B＜C. In addition, calculation based on chemical composition and integral area of M-OH infrared vibration bands reveals that Mg2+ and Fe2+ occupy firstly M₂ and M₁ sites respectively in the crystal lattice of ensignia actinolite jade from Guangxi. The distribution state of Mg2+ and Fe2+ in M₁ and M₃ sites is relatively orderly and the site-occupancy factors are close to 1. Comprehensive analysis demonstrates that the metamorphic grade of ensignia actinolite jade from Guangxi should belong to the greenschist facies category.