Near Infrared Spectroscopy:A New Tool to Identify Different Types of Larderites
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摘要: 寿山石品种繁多，其鉴别和分类也一直是个难题。首次利用便携式近红外光谱仪（NIR）研究了不同类别寿山石的近红外光谱特征。根据寿山石样品状态（块状和粉末状）的不同表面形态、粒度、质量等因素对近红外光谱测试结果的影响进行了分析，讨论了近红外光谱的主要吸收峰归属，旨在探索一种无损、便捷的寿山石鉴别方法。结果表明，利用便携式近红外光谱仪完全可以区分寿山石的三个主要类别，即高山石类（高岭石族）、芙蓉石类（叶蜡石）、汶洋石类（伊利石）。在块状寿山石样品的近红外光谱1 400nm区域，高岭石族矿物表现为一对双峰；叶蜡石和伊利石都仅有一特征单峰，叶蜡石表现为1 392nm，伊利石表现为1 406nm。寿山石样品的表面形态对近红外光谱没有明显的影响。粉末状寿山石样品的近红外光谱吸收峰更为尖锐，分裂程度更好。除了1 400nm处的吸收峰外，在2 180nm左右，高岭石类矿物表现为双峰，而叶蜡石和伊利石为单峰，但叶蜡石的吸收峰位于2 168nm，伊利石位于2 195nm。在条件允许的情况下，获取10mg左右的寿山石样品粉末，便可获得清晰的近红外光谱。Abstract: Due to numerous larderites in the market，it is of a great challenge to identify the genuine ones from the fake ones，not to mention classifying them.However，near infrared spectroscopy（NIR），a new technology to identify larderite，is applied firstly to study the near infrared spectrum characteristics of larderites.In order to obtain sufficient data，the blocky and powdered larderites were respectively tested in several conditions，including different surface morphology，particle size and weight.And the experimental data show that NIR is capable of identifying and classifying larderites mainly based on the differences around 1 400nm，and it is in a more efficient and non－destructive way than XRD does.More specifically，spectra of kaolin－group minerals witness a double peak around 1 400nm.By contrast，spectra of pyrophyllite and illite show a single peak，respectively at 1 392nm and 1 406nm.Apart from the 1 400nm region，another area around 2 180nm exhibits distinguishable features of three types of minerals.Also，a corresponding double－peak can be recognized from the spectra of kaolin－group minerals when samples are grinded into powder，while no peak exhibits in the spectra of blocky sample.In contrast，pyrophyllite，as well as illite，exhibits a single peak in this region.More importantly，the peak positions of pyrophyllite and illite are fundamentally different，respectively at 2 168nm and 2 195nm，which could be used to distinguish pyrophyllite from illite.Additionally，spectral resolution of powdered larderites is much higher than that of blocky samples，which means that the spectrum of the powdered larderites is more accurate than that of blocky ones.In general，by comparing the spectra of minerals in different weight，it is proved that 10mg powdered sample is optimum to obtain their valid and accurate near infrared spectra，meanwhile decreasing damage to a maximum degree.
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Keywords:
- larderite /
- near infrared spectroscopy /
- identification
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