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FTIR imaging in diffusion studies: CO2 and H2O in a synthetic sector-zoned beryl

DOI: 10.3389/feart.2015.00033 DOI Help

Authors: Giancarlo Della Ventura (Roma Tre University) , Francesco Radica (Roma Tre University) , Fabio Bellatreccia (Roma Tre University) , Andrea Cavallo (Istituto Nazionale di Geofisica e Vulcanologia) , Gianfelice Cinque (Diamond Light Source) , Luca Tortora (Istituto Nazionale di Fisica Nucleare) , Harald Behrens (Leibniz Universität)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Frontiers In Earth Science , VOL 3

State: Published (Approved)
Published: June 2015
Diamond Proposal Number(s): 8312 , 8963 , 11425

Open Access Open Access

Abstract: In this work we investigate the strongly inhomogeneous distribution of CO2 and H2O in a synthetic beryl having a peculiar hourglass zoning of Cr due to the crystal growth. The sample was treated at 800°C, 500 MPa, in a CO2-rich atmosphere. High-resolution FESEM images revealed that the hourglass boundary is not correlated to physical discontinuities, at least at the scale of tens of nanometers. Polarized FPA-FTIR imaging, on the other side, revealed that the chemical zoning acts as a fast pathway for carbon dioxide diffusion, a feature never observed so far in minerals. The hourglass zone boundary may be thus considered as a structural defect possibly due to the mismatch induced by the different growth rates of each sector. High-resolution synchrotron-light FTIR imaging, in addition, also allows enhancement of CO2 diffusion along the hourglass boundary to be distinguished from diffusion along fractures in the grain. Therefore, FTIR imaging provides evidence that different diffusion mechanisms may locally combine, suggesting that the distribution of the target molecules needs to be carefully characterized in experimental studies. This piece of information is mandatory when the study is aimed at extracting diffusion coefficients from analytical profiles. Combination of TOF-SIMS and FPA data shows a significant depletion of type II H2O along the hourglass boundary, indicating that water diffusion could be controlled by the distribution of alkali cations within channels, coupled to a plug effect of CO2.

Journal Keywords: Beryl; Co2 Diffusion; Hourglass Zoning; Ftir-Fpa Imaging; Synchrotron Radiation; Fesem; Empa; Tof-Sims

Subject Areas: Earth Science, Materials, Chemistry

Diamond Offline Facilities: FTIR
Instruments: B22-Multimode InfraRed imaging And Microspectroscopy

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