Crystal Chemical Characterisation of Red Beryl by 'Standardless' Laser-Induced Breakdown Spectroscopy and Single-Crystal Refinement by X-Ray Diffraction: An Example of Validation of an Innovative Method for the Chemical Analysis of Minerals

摘要

Laser-induced breakdown spectroscopy (LIBS) is a valuable technique for performing qualitative and quantitative chemical determinations of all elements in one shot, including low atomic number elements such as Li and Be. This technique does not require any sample preparation to reveal the atomic species, even when present in trace amounts (m/m). In this study, for the first time, we provide an accurate mineral formula for a Cs-rich red beryl by combining crystallographic data obtained using the traditional single-crystal X-ray diffraction technique and quantitative chemical data obtained with an innovative 'standardless' method: Calibration-free-LIBS (CF-LIBS). In particular, a new LIBS prototype coupled with a petrographic microscope (CF-mu LIBS) was used to analyse chemically homogeneous areas of about 10 mu m spot size, causing minimal damage to the mineral. The results showed that calibration-free quantitative analysis is suitable for the quantification of major and minor low and high atomic number elements in beryl. The accuracy of quantification of low atomic number elements by CF-mu LIBS led to the empirical formula: (12])(Cs0.006Na0.019K0.017Ca0.019)(Sigma 0.061) ([4])(Be2.989Li0.011)(Sigma 3.000) ([6])(Ti0.053Mn0.051Mg0.007Al1.890)(Sigma 2.000) ([4])(Be0.116Fe0.024Si5.860)(Sigma 6.000)O-18. This formula is consistent with the crystal-structure refinement data and demonstrates the validity of CF-mu LIBS for chemical analyses of minerals containing low atomic number elements.