Near Infrared Spectroscopy:A New Tool to Identify Different Types of Larderites

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.