Minerals of the ammonioalunite—ammoniojarosite series formed on a burning coal dump at Czerwionka, Upper Silesian Coal Basin, Poland

Jehlička

2018

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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Jehlička

2018

Field identification of minerals at burning coal dumps using miniature Raman spectrometers

Jehlička

2017

Earthy, finely crystalline, weathering, and condensation products sometimes occur at the surface and subsurface of waste dumps or burning coal dumps which remain after coal mining. Surface crusts at the burning dumps of bituminous coal at Heřmanice (Silesia, Czech Republic) were investigated using a lightweight portable Raman spectrometer. The compact instrument, with 785‐nm diode excitation, allowed for the recording of good quality Raman spectra, and for the identification of a series of more‐or‐less complex sulfates (mascagnite, letovicite, sabieite, pyracmonite) as well as common sal ammoniac and sulfur. The great complexity of the mineral associations is demonstrated in aggregates of efremovite, godovikovite, boussingaultite, and sabieite. In this case, the handheld instrumentation does not allow for ideal detection and discrimination of finely crystalline minerals in complex mixtures. Copyright © 2017 John Wiley & Sons, Ltd.

Raman spectroscopy of anhydrous and hydrated aluminum sulfates: Experience from burning coal heaps

Rousaki

et al. 2022

Hydrated aluminum‐rich sulfates belong to less widespread secondary minerals on Mars, which are probably connected with hydrothermal alterations. On Earth, such sulfates result from acidic weathering of aluminosilicates, and their formation is controlled by factors such as pH, temperature, or water activity. Physical–chemical conditions can be reconstructed if specific sulfate phases are detected, and therefore, the investigation of sulfate assemblages in high‐temperature settings is important for planetology and exobiology research. Raman spectroscopy is a powerful analytical tool for the discrimination of sulfates, and the degree of hydration, which is a sensitive marker of temperature conditions, can be tracked using this method. However, spectral similarities of sulfates and metastability and rapid transformations may hinder their correct identification. We take advantage of in situ and laboratory Raman spectroscopy to characterize uncommon anhydrous and hydrated Al‐NH4 sulfate mineralogy which forms under elevated temperature at the Anna burning coal waste dump, Alsdorf, Germany, and can be considered as analogous to fumarolic environments. We detected a suite of hydrated Al sulfates (e.g. alunogen, khademite, and tschermigite) in the medium‐temperature zones (~50°C). To minimize possible rehydration processes, we deployed two miniaturized Raman spectrometers (532 and 1064 nm) for field investigations in the high‐temperature zone (~130°C to 150°C). Mixtures of anhydrous (godovikovite and millosevichite) and hydrated phases along with intermediate phases were detected in the field as well as in the laboratory. Such observations are consistent with the premise that the degree hydration of sulfates increase with decreasing temperature. These results confirm that Raman spectroscopy is, despite several analytical challenges, capable of distinguishing Al sulfates, and their hydration states, within complex aggregates and crusts, and future applications in planetary research are promising.