Chemical and\nAcoustical Mixed-Mapping of Geological\nMaterials from Laser-Induced Plasmas: A Comprehensive Approach to\nDifferentiate Mineral Phases

The acoustic wave produced alongside laser-induced plasmas\ncan\nbe used in conjunction with the recorded atomic spectra of plasma\nemission to expand the physicochemical information acquired from a\nsingle inspection event. Among the most interesting uses of acoustic\ninformation is the differentiation of mineral phases with similar\noptical responses coexisting in geological targets. In addition, laser-induced\nplasma acoustics (LIPAc) can provide data related to the inspected\nmaterial's hardness, density, and compactness. In this paper,\nwe present\na dual acoustic–optic laser-based strategy for the generation\nof high-resolution surface images of mineral samples. By combining\nsimultaneous multimodal LIBS (laser-induced breakdown spectroscopy)\nand LIPAc spectral data from laser-induced plasmas, we explore the\nmineralogical composition of rocks embedded in resin matrixes to distinguish\ntheir chemical composition as well as their crystal phases based on\nphysical changes caused by the different spatial arrangements of the\nconstituent atoms. The multispectral polyhedron created by merging\nsingular optical maps, one per detected elements, and the coincidental\nacoustic map enhance the distinction between regions present within\nthe matrix of a host rock as compared to the differentiation yielded\nby each technique when used separately. The chemical information guides\nthe composition of the mineral phases in the host rock. Then, the\nphysical information obtained from acoustics may reinforce the identification\nof the detected mineral phase, draw the geological history of the\ninspected section, and showcase possible transformations, mainly of\npolymorphic nature. To test the combination proposed herein, we also\ninspected a septarian nodule featuring an ensemble of mineral phases\nwith different origins. Mixed optical and acoustic responses from\nlaser-produced plasmas of this complex sample allowed us to obtain\nmore specific information. This approach constitutes a reliable and\nhigh-throughput tool for studying the surface of geological samples,\nwhich can substantially supplement well-established techniques for\nmineralogical analysis such as Raman spectroscopy and X-ray diffraction.