Analysis of garnet by LIBS — two practical applications

Publication: Peter A. Defnet, Michael A. Wise, Russell S. Harmon, Richard R. Hark and Keith Hilferding. “Analysis of Garnet by Laser-Induced Breakdown Spectroscopy—Two Practical Applications,” Minerals 11, 705 (2021). This study evaluated two practical applications of handheld LIBS using SciAps Z-300—validation of labels assigned to garnets in museum collections, and discrimination of LCT (lithium-cesium-tantalum) and NYF (niobium, yttrium and fluorine) pegmatites based on garnet geochemical fingerprinting—both of which could be implemented on site in a museum or field setting with a handheld LIBS analyzer.

Above: Spectral processing and chemometric procedure flow diagram for this study.Below: PCA scores plots for processed LIBS broadband spectra for the training set of 172 garnets (31 almandines, 33 andradites, 46 grossulars, 17 pyropes, 39 spessartines, and 6 uvarovites) acquired with the RT-100 laboratory system (upper left) and Z-500 handheld analyzer (lower right) showing respective Fe3+–Al–Cr, Fe2+–Mn, and Fe2+–Mg trends.

Abstract: Laser-induced breakdown spectroscopy (LIBS) is a simple and straightforward technique of atomic emission spectroscopy that can provide multi-element detection and quantification in any material, in-situ and in real time because all elements emit in the 200–900 nm spectral range of the LIBS optical emission. This study evaluated two practical applications of LIBS—validation of labels assigned to garnets in museum collections, and discrimination of LCT (lithium-cesium-tantalum) and NYF (niobium, yttrium and fluorine) pegmatites based on garnet geochemical fingerprinting—both of which could be implemented on site in a museum or field setting with a handheld LIBS analyzer. Major element compositions were determined using electron microprobe analysis for a suite of 208 garnets from 24 countries to determine garnet type. Both commercial laboratory and handheld analyzers were then used to acquire LIBS broadband spectra that were chemometrically processed by partial least squares discriminant analysis (PLSDA) and linear support vector machine classification (SVM). High attribution success rates (>98%) were obtained using PLSDA and SVM for the handheld data suggesting that LIBS could be used in a museum setting to assign garnet type quickly and accurately. LIBS also identifies changes in garnet composition associated with increasing mineral and chemical complexity of LCT and NYF pegmatites.

‍Keywords: garnet; laser-induced breakdown spectroscopy; LIBS; electron microprobe analysis; geochemical fingerprinting; chemometrics; PCA; PLSDA; SVM

‍Access to publication: https://doi.org/10.3390/min11070705

‍About this journal: Minerals is an international, peer-reviewed, open access journal of natural mineral systems, mineral resources, mining, and mineral processing. Minerals is published monthly online by MDPI.