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.

本研究中所使用的矿物均由澳大利亚博物馆（ASM）提供。这些矿物通过X射线衍射（XRD）和电感耦合等离子体原子发射光谱法（ICP-AES）技术进行了表征。

所采用的样品包括：（a）来自墨西哥下加利福尼亚州圣罗莎的阿梅莉亚矿的ASM-D49056硼镁石；（b）来自墨西哥下加利福尼亚州的贝列奥的ASM-D27575铜镁石；（c）来自美国亚利桑那州蒂格的曼诺斯矿的ASM D36845辉石；（d）来自澳大利亚南澳 Broken Hill的Consols矿的ASM D191881磷灰石。

矿物晶体被放置并定向于Olympus BHSM显微镜载物台的抛光金属表面上，该显微镜配备了10倍和50倍物镜。该显微镜是Renishaw 1000拉曼显微镜系统的一部分，该系统还包括单色仪、滤光系统以及电荷耦合器件（CCD）。拉曼光谱由Spectra-Physics型号127的He-Ne激光器（633 nm）激发，在100至4000 cm^-1范围内以2 cm^-1的分辨率获得。通过最高放大倍数下的重复采集，以改善光谱的信噪比。光谱使用硅片520.5 cm^-1的线条进行校准。

使用Nicolet Nexus 870傅里叶变换红外光谱仪和智能耐久单跳钻石ATR池获得了红外光谱。通过64次扫描的叠加，以4 cm^-1的分辨率和0.6329 cm/s的镜面速度，在4000至525 cm^-1范围内获得了光谱。

使用Spectracalc软件包GRAMS（Galactic Industries Corporation，新罕布什尔州，美国）对光谱进行了基线调整、平滑和归一化处理。使用Jandel ‘Peakfit’软件包进行了波段成分分析，该软件包允许选择拟合函数的类型，并允许相应地固定或调整特定参数。波段拟合使用高斯-洛伦兹交叉乘积函数，并使用最小数量的成分波段进行拟合。高斯-洛伦兹比保持在>0.7，拟合直至获得可重复的结果，其平方相关系数r^2>0.995。

图1展示了（a）磷灰石、（b）硼镁石、（c）辉石和（d）铜镁石的羟基伸缩区域的拉曼光谱。图2显示了（a）辉石和（b）铜镁石的羟基伸缩区域拉曼光谱的波段成分分析。图3展示了（a）硼镁石、（b）辉石和（c）铜镁石的600-1000 cm^-1区域的拉曼光谱。图4展示了磷灰石的碳酸盐区域的拉曼光谱。图5展示了（a）磷灰石、（b）硼镁石、（c）辉石和（d）铜镁石的100-500 cm^-1区域的拉曼光谱。