Synthesis and characterization of Fe(III)-Fe(II)-Mg-Al smectite solid solutions and implications for planetary science

Abstract This study demonstrates the synergies and limits of multiple measurement types for detection smectite chemistry oxidation state on planetary surfaces to infer past geochemical conditions. Smectite clay minerals are common products water-rock interactions throughout solar system, their characterization provides important clues about conditions environments if sufficient information composition can be discerned. Here, we synthesize report spectroscopic properties a suite samples that span intermediate compositional range between Fe(II), Fe(III), Mg, Al end-member species using bulk chemical analyses, X-ray diffraction, Vis/IR reflectance spectroscopy, UV green-laser Raman Mössbauer spectroscopy. Our data show octahedral Fe reliably identified in near infrared basis combination fundamental metal-OH stretching modes 2.1–2.9 ?m, which vary systematically with chemistry. Smectites dominated by Mg or Fe(III) have spectrally distinct stretches, whereas Al-rich Fe(II)-rich smectites similar minima 2.76 but M-OH features 2.24 2.36 ?m. We expanded spectral libraries include both Fe(II) states, more refined from MIR is now possible, as position 450 cm–1 absorption shifts content, although detailed analysis best accomplished concert other methods. also provide first clays function chemistry, demonstrate spectroscopy at excitation wavelengths qualitatively distinguish different structures enhance interpretation analyses. sample set how diffraction dioctahedral trioctahedral either (02,11) (06,33) peaks, auxiliary aids specific identifications. Finally, temperature-dependent isomer shift quadrupole splitting insensitive changes content reliability differentiates within mineral structure.