Raman spectroscopy of the minerals boléite, cumengéite, diaboléite and phosgenite: implications for the analysis of cosmetics of antiquity

The minerals used in this study were supplied by the Australian Museum (ASM). The minerals have been characterized by both X-ray diffraction (XRD) and by chemical analysis using ICP-AES (inductively coupled plasma atomic emission spectroscopy) techniques.

The following samples were used: (a) sample ASM-D49056 boléite from the Amelia Mine, Santa Rosalia, Baja, California, Mexico; (b) sample ASM-D 27575 cumengéite, Beleo, Baja California, Mexico; (c) sample ASM D36845 diaboléite from Mannoth mine, Tiger, Arizona, USA; and (d) sample ASM D191881 phosgenite from Consols mine, Broken Hill, South Australia.

Crystals of the minerals were placed and orientated on a polished metal surface on the stage of an Olympus BHSM microscope, which is equipped with 10 × and 50 × objectives. The microscope is part of a Renishaw 1000 Raman microscope system, which also includes a monochromator, a filter system and a Charge Coupled Device (CCD). Raman spectra were excited by a Spectra-Physics model 127 He-Ne laser (633 nm) at a resolution of 2 cm−1 in the range between 100 and 4000 cm−1. Repeated acquisition using the highest magnification was accumulated to improve the signal to noise ratio in the spectra. Spectra were calibrated using the 520.5 cm−1 line of a silicon wafer.

Infrared (IR) spectra were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart endurance single bounce diamond ATR cell. Spectra over the 4000 to 525 cm−1 range were obtained by the co-addition of 64 scans with a resolution of 4 cm−1 and a mirror velocity of 0.6329 cm/s.

Spectroscopic manipulation such as baseline adjustment, smoothing and normalization were performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, New Hampshire, USA). Band component analysis was undertaken using the Jandel ‘Peakfit’ software package, which enabled the type of fitting function to be selected and allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Gauss-Lorentz cross-product function with the minimum number of component bands used for the fitting process. The Gauss-Lorentz ratio was maintained at values >0.7 and fitting was undertaken until reproducible results were obtained with squared correlations of r2 >0.995.

Figure 1 is Raman spectra of the hydroxyl-stretching region of (a) phosgenite, (b) boléite, (c) diaboléite and (d) cumengéite.  Figure 2 shows band component analysis of the hydroxyl-stretching region of the Raman spectrum of (a) diaboléite and (b) cumengéite. Figure 3 is Raman spectra of the 600–1000 cm−1 region of (a) boléite, (b) diaboléite and (c) cumengéite.  Figure 4 is Raman spectra of the carbonate region of phosgenite. Figure 5 is Raman spectra of the 100–500 cm−1 region of (a) phosgenite, (b) boléite, (c) diaboléite and (d) cumengéite.

本研究所用矿物由澳大利亚博物馆（Australian Museum, ASM）提供。所有矿物均通过X射线衍射（X-ray diffraction, XRD）及电感耦合等离子体原子发射光谱（inductively coupled plasma atomic emission spectroscopy, ICP-AES）技术完成表征。

本次实验使用的样品如下：(a) 样品ASM-D49056 块铜矾（boléite），采集自墨西哥下加利福尼亚州圣罗萨莉亚市阿米莉亚矿；(b) 样品ASM-D27575 硫铜银矿（cumengéite），采集自墨西哥下加利福尼亚州贝莱奥市；(c) 样品ASM-D36845 斜方锑铜铅矿（diaboléite），采集自美国亚利桑那州泰格市曼诺思矿；(d) 样品ASM-D191881 磷氯铅矿（phosgenite），采集自澳大利亚南澳大利亚州布罗肯希尔市康索尔矿。

将矿物晶体放置于奥林巴斯BHSM显微镜载物台的抛光金属表面并完成定向，该显微镜配备10×及50×物镜。此显微镜隶属于雷尼绍1000型拉曼显微镜系统，该系统还包含单色仪、滤光片系统及电荷耦合器件（Charge Coupled Device, CCD）。拉曼光谱由Spectra-Physics 127型氦氖（He-Ne）激光器（波长633 nm）激发，光谱分辨率为2 cm⁻¹，采集范围为100~4000 cm⁻¹。采用最高放大倍率进行多次重复采集以提升光谱信噪比。以硅片的520.5 cm⁻¹谱线对光谱进行校准。

红外（Infrared, IR）光谱通过搭载智能Endurance单次反射金刚石ATR池的Nicolet Nexus 870型傅里叶变换红外（FTIR）光谱仪采集得到。光谱采集范围为4000~525 cm⁻¹，通过累加64次扫描获得，分辨率为4 cm⁻¹，镜动速度为0.6329 cm/s。

光谱处理操作（包括基线校正、平滑及归一化）通过Spectracalc软件包GRAMS（美国新罕布什尔州Galactic Industries Corporation出品）完成。谱峰组分分析采用Jandel公司的"Peakfit"软件包实现，该软件支持拟合函数类型选择，并可根据需求固定或调整特定参数。谱峰拟合采用高斯-洛伦兹（Gauss-Lorentz）交叉乘积函数，且以最少的组分谱峰完成拟合流程。高斯-洛伦兹比值维持在0.7以上，拟合过程持续至获得可重复结果，此时平方相关系数r²>0.995。

图1为(a) 磷氯铅矿（phosgenite）、(b) 块铜矾（boléite）、(c) 斜方锑铜铅矿（diaboléite）及(d) 硫铜银矿（cumengéite）的羟基伸缩区域拉曼光谱。图2展示了(a) 斜方锑铜铅矿及(b) 硫铜银矿拉曼光谱羟基伸缩区域的谱峰组分分析结果。图3为(a) 块铜矾、(b) 斜方锑铜铅矿及(c) 硫铜银矿的600~1000 cm⁻¹区域拉曼光谱。图4为磷氯铅矿的碳酸盐区域拉曼光谱。图5为(a) 磷氯铅矿、(b) 块铜矾、(c) 斜方锑铜铅矿及(d) 硫铜银矿的100~500 cm⁻¹区域拉曼光谱。