湖北竹山“油松”的红外光谱特征及其成分研究

湖北省十堰市竹山县秦古镇小林扒矿区产出了一类较为特殊的绿松石。这类绿松石颜色多为浅绿色、浅黄绿色或浅苹果绿色，产出原石具滑感，性脆，亦称之为“油松”。与其结构细腻度相当的绿松石原料相比，此类绿松石密度普遍明显偏低，硬度偏小；经传统有机结合剂充填处理后，致密度及硬度均未见明显改善，无法作为首饰级材料使用，造成绿松石这类不可再生的宝贵资源严重浪费。以“油松”为研究对象，采用常规宝石学测试仪器、红外吸收光谱仪、X射线粉晶衍射仪、电子探针仪以及环境扫描电子显微镜等对其化学组分及显微结构特征等进行测试，为有效利用这类绿松石资源提供科学依据。测试结果表明，“油松”的相对密度为2.04～2.22；在长波和短波紫外光下荧光反应均显示为惰性。“油松”的红外吸收光谱谱带主要分布在3 700~3 090 cm-1以及1 638~466 cm-1范围内，其中3 509和3 462 cm-1处峰形尖锐的OH致吸收光谱、3 277和3 090 cm-1 附近较宽缓的结晶水致吸收光谱特征与绿松石的官能团区吸收特征一致。“油松”在高频区3 700和3 622 cm-1处具有高岭石或蒙脱石中OH 致弱红外吸收谱峰。在1 638 cm-1附近均出现有强度中等的较为宽缓的吸收峰，该吸收峰与绿松石中H₂O的弯曲振动致吸收谱峰一致。指纹区的吸收峰峰形及峰位均与一般绿松石有较大差异，为Si-O及P-O的混合吸收谱峰。“油松”的主要化学组成元素为Si，Al和P，含有少量的Fe和Cu，并含有微量的Mg，Ca及Cr。组成元素的氧化物含量分别为：w(SiO₂)：25.60%～30.90%，w(Al₂O₃)：26.55%～28.29%，w(FeO_T)：5.35%～5.90%，w(P₂O₅)：22.00%～23.52%，w(CuO)：5.10%～5.87%。“油松”中的Al₂O₃和P₂O₅的含量均低于绿松石成分理论值及其他各产地的天然绿松石。相对于天然绿松石中较低的SiO₂含量（0.02%～0.12%），“油松”中SiO₂的含量明显偏高，均高于25%。“油松”的主要组成矿物为绿松石，并含有一定量的粘土矿物蒙脱石及蒙脱石-高岭石，其硬度低，具有滑感，是“油松”硬度低，具有滑感且优化处理效果不显著的主要原因。

Infrared Spectral Characteristics and Composition of the“Oily Turquoise”in Zhushan,Hubei

In recent years,a relatively unique turquoise variety has been found in the Xiaolinpa ore district in Qingu Town,Zhushan County,Shiyan City of Hubei Province.The color of this turquoise variety is mostly light green,light yellow green,or light apple green.The rough material is slippery feel and brittle.As a result,it is called“oily turquoise”by a local citizen.Compared to the turquoise with similar structure fineness,the density of turquoise is generally lower,and the hardness is smaller,with the Mohs hardness ranges from 3 to 4.This type of turquoise has not been significantly improved in hardness and structural density after being filled with a traditional organic binder,and cannot be used as a gem-quality turquoise material for jewelry.The conventional gemological instruments,infrared absorption spectrometers,X-ray powder crystal diffractometers,electron probes microscopic analysis,and environmental scanning electron microscopes were used to study the chemical composition and microstructure characteristics of the“oily turquoise”.The results show that the specific gravity of the“oily turquoise”range 2.04 from 2.22,which was lower than that of typical turquoise.It shows inert fluorescence under long-wave and short-wave UV light.The infrared absorption spectrum of the“oily turquoise”is mainly distributed in the range of 3700 to 3090 and 1638 to 466 cm^-1,of which the peaks at 3509 cm^-1±and 3462 cm^-1±have sharp OH-induced absorption spectra,and the broader crystallization water-induced absorption spectra at 3277 cm^-1±and 3090 cm^-1±are consistent with the absorption characteristics of the turquoise functional group region.It has weak OH-induced infrared absorption peaks in kaolinite or montmorillonite at high frequencies of 3700 and 3622 cm^-1.Relatively broad absorption band around 1638 cm^-1,with moderate intensity agree with the absorption peak of the bending vibration induced by H₂O in turquoise.The shape and position of the absorption peaks in the fingerprint region of the“oily turquoise”are quite different from those of typical turquoise;they are mixed absorption spectrum peaks of Si—O and P—O.The main chemical composition of the“oily turquoise”is SiO 2,Al₂O₃,FeO_T,P₂O₅and CuO,with small amounts of MgO,CaO and Cr 2O 3.The content of SiO 2 is 25.60%to 30.90%,and the content of Al₂O₃is 26.55%to 28.29%,FeO_Tcontent is 5.35%to 5.90%,P₂O₅content is 22.00%to 23.52%,and CuO content is 5.10%to 5.87%.Compared with another typical natural turquoise,the“oily turquoise”contains a higher content of SiO 2,which is higher than 25%.The main constituent mineral of the“oily turquoise”is turquoise,and it contains a certain amount of montmorillonite and montmorillonite-kaolinite.The low hardness and slippery characteristics of the“oily turquoise”are relevant to montmorillonite that results in the insignificant optimization effect.