Raman spectroscopic study of six synthetic anhydrous sulfates relevant to the mineralogy of fumaroles

Abstract

Fumaroles, vents that emit hot gases and vapor, are an accompanying phenomenon of volcanic activity. Such phenomena are also observed within the framework of self‐ignited burning coal seams and coal heap fires, if less commonly. The high temperatures and chemical reactions between the gas and solid phases are responsible for extensive alteration of surrounding rocks, resulting in mineral encrustations of unusual compositions. Rare anhydrous sulfates (millosevichite, mikasaite, efremovite, godovikovite, sabieite, and steklite) are signature minerals of fumarole encrustations. Comprehensive Raman data for these anhydrous phases are required for the successful identification of natural samples by Raman spectroscopy. Six synthetic equivalents of the natural anhydrous sulfates were prepared by heating of the hydrated analogues and were investigated using both a bench‐top Raman microspectrometer and a portable Raman spectrometer. This comparative approach can help further steps for the successful deployments of miniature Raman tools in situ under field conditions. The studied anhydrous sulfates displayed distinctive Raman spectra of their crystalline phases. Compared with their fully hydrated counterparts, a shifting of bands of the ν1 symmetric stretching mode was observed in the Raman spectra of all samples. Isostructural millosevichite and mikasaite have very distinctive Raman spectra; however, structurally related godovikovite, sabieite, and steklite show very similar spectral shapes. For ammonium‐bearing phases (efremovite, godovikovite, sabieite), the Raman signatures of the NH4 group were observable at >2,800 cm−1 and in the 1,400–1,800 cm−1 region. Our measurements show that the performance of a light‐weight portable Raman spectrometer with near infrared excitation was sufficient for the unambiguous discrimination of the investigated sulfates.

Raman spectroscopic vibrational analysis of the complex iron sulfates clairite, metavoltine, and voltaite from the burning coal dump Anna I, Alsdorf, Germany

“…Here, we cannot observe these ammonium bands distinct from the strong water hydrogen-bonded features, which occur very close to their expected positions in wavenumber. The Raman spectrum of clairite is also very different from other ammonium-iron sulfates, for example, pyracmonite and sabieite, [29,30] although these minerals share strong spectral features with respect to Fe-O vibrations. The table of Raman bands of clairite and their assignments can be found in Table 2.…”

Uptake of gaseous thallium, tellurium, vanadium and molybdenum into anhydrous alum, Lascar volcano fumaroles, Chile

“…Raman spectra (Fig. 3) show the characteristic vibration bands of (1) anhydrous alums, with major occurrence of (NH4)Al(SO4)2 (godovikovite bands at 318, 483, 610 and 653, 1076, 1287, 3148, 3208, 3331 cm -1 ), and minor occurrence of (NH4)Fe(SO4)2 (sabieite main band at 1033 cm -1 ) and (NH4)2Mg2(SO4)3 (efremovite main band at 1049 cm -1 ) (Kosek et al, 2018); (2) hydrated sulphates including MgSO4•6H2O (exahydrite bands at 460±5, 610, 983-984, 1080 and 3435 cm -1 ), mirabilite (Na2SO4•10H2O) and/or hydrated alums (band at 990/991 cm -1 ); and (3) CaSO4 (anhydrite bands at 416, 499, 609, 627, 675, 1017 and 1129 cm -1 ) (Frezzotti et al, 2012). The average K/Al atomic ratio of 0.10±0.05 (1) is consistent with minor occurrence of K in godovikovite (Shimobayashi et al, 2011).…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…Kosek and co‐workers carried out a Raman study of six synthetic anhydrous sulfates relevant to the mineralogy of fumaroles. Their measurements show that the performance of a lightweight portable Raman spectrometer with near IR excitation was sufficient for the unambiguous discrimination of the investigated sulfates . Makreski and co‐workers measured the IR and Raman spectra the rare‐occurring complex hydrogen arsenate minerals pharmacolite, picropharmacolite, and vladimirite.…”

“…Their measurements show that the performance of a lightweight portable Raman spectrometer with near IR excitation was sufficient for the unambiguous discrimination of the investigated sulfates. [153] Makreski and co-workers measured the IR and Raman spectra the rare-occurring complex hydrogen arsenate minerals pharmacolite, picropharmacolite, and vladimirite. They showed an improved ability of Raman over IR spectroscopy to discriminate arsenate and hydrogen arsenate units.…”