Multi-scale characterization of glaucophane from Chiavolino (Biella, Italy): implications for international regulations on elongate mineral particles

• Published in: European journal of mineralogy (Stuttgart) 2021-02, Vol.33 (1), p.77-112
• Main Authors: Vigliaturo, Ruggero, Elkassas, Sabrina M, Ventura, Giancarlo Della, Redhammer, Günther J, Ruiz-Zepeda, Francisco, O'Shea, Michael J, Dražić, Goran, Gieré, Reto
• Format: Article
• Language: English
• Subjects: Amphiboles; Composition; Electron energy; Electron energy loss spectroscopy; Electron probe microanalysis; Elongation; Energy dispersive X ray spectroscopy; Fourier transforms; Geology; Infrared spectroscopy; International regulations; Light microscopy; Metamorphic rocks; Metamorphism; Mineralogical research; Morphology; Mossbauer spectroscopy; Optical microscopy; Optical properties; Particulates; Public health; Raman spectroscopy; Regulations; Risk assessment; Sample preparation; Scanning electron microscopy; Structure; Transmission electron microscopy; X ray powder diffraction; X-ray diffraction; X-ray spectroscopy
• ISSN: 1617-4011; 0935-1221; 1617-4011
• DOI: 10.5194/ejm-33-77-2021

In this paper, we present the results of a multi-analytical characterization of a glaucophane sample collected in the Piedmont region of northwestern Italy. Investigation methods included optical microscopy, powder X-ray diffraction, Fourier-transform infrared spectroscopy, μ-Raman spectroscopy, Mössbauer spectroscopy, electron probe microanalysis, environmental scanning electron microscopy and energy-dispersive X-ray spectroscopy, and scanning/transmission electron microscopy combined with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. In addition to the crystal-chemical characterization of the sample from the mesoscale to the near-atomic scale, we have also conducted an extended study on the morphology and dimensions of the mineral particles. The main finding is that studying the same particle population at different magnifications yields different results for mineral habit, dimensions, and dimensional distributions. As glaucophane may occur as an elongate mineral particle (e.g., asbestiform glaucophane occurrences in California and Nevada), the observed discrepancies therefore need to be considered when assessing potential breathability of such particles, with implications for future regulations on elongate mineral particles. While the sample preparation and particle counting methods are not directly investigated in this work, our findings suggest that different magnifications should be used when characterizing an elongate mineral particle population, irrespective of whether or not it contains asbestiform material. These results further reveal the need for developing improved regulation for elongate mineral particles. We thus propose a simple methodology to merge the datasets collected at different magnifications to provide a more complete description and a better risk evaluation of the studied particle population.