内蒙古固阳浅黄色系长石的谱学特征研究

Spectral Characteristics of Light Yellow Feldspar From Guyang, Inner Mongolia

内蒙古每年可开采多达100 t黄色至无色的长石,且透明度良好、分布集中,加以处理以顺应市场需求,固阳长石可作为极具发展前景的宝石资源。采用激光拉曼光谱、 X射线荧光光谱、傅里叶变换红外光谱、电子探针一系列测试技术,以及常规宝石学测试方法对内蒙古固阳县长石的基本宝石学特征、化学组成成分及振动光谱特征等进行了系统的研究。结果表明,该产地长石原石样品的晶形大多是成砾石状,折射率为1.555~1.570,双折射率为0.008~0.010,密度在2.65~2.68 g·cm^(-3),样品的紫外荧光特征显示,在长波(365 nm)和短波(254 nm)下均为惰性。X射线荧光光谱仪分析表明,所有样品中均含有一定量的Al、 Si、 Ca,以及少量的Ti、 Fe、 Mn、 Mg和Sr。根据电子探针测试结果计算长石的化学分子式及端元组分比例可知,该类样品属于中长石。长石的红外吸收谱峰主要位于1 200~400 cm^(-1)之间。其中从钠长石到钙长石,随长石牌号递增,在红外吸收光谱中则表现为:590和650 cm^(-1)的吸收峰均向低波数范围偏移,分别偏移至575 cm^(-1)±和624 cm^(-1)±处,本文研究的固阳中长石,两处的吸收峰分别位于578和632 cm^(-1)处,符合长石序列红外光谱变化的特征,属典型中长石红外吸收光谱特征。该类长石的拉曼谱峰主要由102、 186、 290、 489、 516、 572和800 cm^(-1)七个主要的拉曼谱峰组成。其中450 cm^(-1)以下的102、 186和290 cm^(-1)谱峰是由金属阳离子和氧([M—O])之间的振动,290和490 cm^(-1)两处拉曼峰的分裂程度可以指示硅酸盐矿物中Al/Si的有序度。489、 516和572 cm^(-1)处拉曼峰属O—Si(Al)—O的弯曲振动频谱和Si—Obr—Si(Al)的反对称伸缩。与其他产地长石对比分析可作为鉴别依据之一。基于以上分析,进行了此种长石的组成成分与主要结构的分析和探讨。

Inner Mongolia can mine up to 100 tons of yellow to colorless feldspar yearly,with good transparency and concentrated distribution.It can be treated to meet the market demand.Guyang feldspar can be used as a gem resource with great development prospects.In this paper,the basic gemological characteristics,chemical composition and vibration spectral characteristics of feldspar in Guyang County,Inner Mongolia are systematically studied by using a series of testing technologies such as laser Raman spectroscopy,X-ray fluorescence spectroscopy,Fourier transforms infrared spectroscopy,electron probe and conventional gemological testing methods.The results show that the crystal form of feldspar raw stone samples in this area is mostly gravel,the refractive index is 1.555~1.570,the birefringence is 0.008~0.010,and the density is 2.65~2.68 g·cm^(-3).The UV fluorescence characteristics of the samples show that they are inert under long waves(365 nm)and short waves(254 nm).X-ray fluorescence spectrometer analysis shows that all samples contain a certain amount of Al,Si and Ca,and a small amount of Ti,Fe,Mn,Mg and Sr.According to the chemical molecular formula calculation and the proportion of end groups of feldspar according to the test results of electron microprobe,this kind of sample belongs to medium feldspar.The infrared absorption peak of feldspar is mainly between 1200~400 cm^(-1).From albite to anorthite,it increases with the grade of feldspar.In the infrared absorption spectrum,the absorption peaks of 590 and 650 cm^(-1) are shifted to the low wavenumber range,to 575 cm^(-1)±and 624 cm^(-1)±respectively.The absorption peaks of Guyang middle feldspar studied in this paper are located at 578 and 632 cm^(-1) respectively,which is in line with the characteristics of the infrared spectrum changes of feldspar sequence and belongs to the infrared absorption spectrum characteristics of typical middle feldspar.The Raman peaks of this kind of feldspar are composed of seven main Raman peaks:102,186,290,489,516,572 and 800 cm^(-1).The 102,186 and 290 cm^(-1) peaks below 450 cm^(-1) are caused by the vibration between metal cations and oxygen([M—O]).The splitting degree of the Raman peaks at 290 cm^(-1) and 490 cm^(-1) can indicate the order of Al/Si in silicate minerals.The Raman peaks at 489,516 and 572 cm^(-1) belong to the bending vibration spectrum of O—Si(AL)—O and the antisymmetric stretching of Si OBR Si(AL).The comparative analysis with feldspar from other producing areas can be used as one of the identification basis.Based on the above analysis,this feldspar’s composition and main structure are analyzed and discussed.