Raman spectroscopy study of manganese oxides: Tunnel structures

Abstract

Raman spectra were collected for an extensive set of well-characterized tunnel-structure Mn oxide mineral species employing a range of data collection conditions. Using various laser wavelengths, such as 785, 633, and 532 nm at low power levels (30–500 µW), as well as the comprehensive database of standard spectra presented here, it is generally possible to distinguish and identify the various tunnel structure Mn oxide minerals. The Raman mode relative intensities can vary significantly as a function of crystal orientation relative to the incident laser light polarization direction as well as laser light wavelength. Consequently, phase identification success is enhanced when using a standards database that includes multiple spectra collected for different crystal orientations and with different laser light wavelengths. For the hollandite-group minerals, the frequency of the Raman mode near 630 cm–1 shows a strong linear correlation with the fraction of Mn3+ in the octahedral Mn sites. With the comprehensive Raman database of well-characterized Mn oxide standards provided here (and available online as Supplemental Materials1), and use of appropriate data collection conditions, micro-Raman is a powerful tool for identification and characterization of biotic and abiotic Mn oxide phases from diverse natural settings, including on other planets.

Multi-Technique Diagnostic Analysis of Plasters and Mortars from the Church of the Annunciation (Tortorici, Sicily)

“…In particular, XRF results (Figure 5b) indicate an elemental composition based on Ca, Fe, and Mn. In the corresponding Raman spectrum (Figure 5c), the weak peaks observed in the range from ~300 to ~1300 cm −1 , can be ascribed to manganese and iron oxides-hydroxides [30,31], in agreement with the detection of Mn and Fe by XRF. These observations indicate that the investigated point was made by starting from the use of complex pigments derived from Mn-based and Fe-based products, such as the raw and/or burnt umber [32].…”

“…Furthermore, the weak band at ~1087 cm −1 indicates the presence of the preparation ground likely made of calcium carbonate (CaCO 3 ). Moreover, peaks in the 160-700 cm −1 range can be assigned to some iron and manganese oxides and hydroxides [24][25][26][27][28][29][30][31] commonly present in some red earths. The bands related to the carbon-based materials (at ~1300 and ~1600 cm −1 ) are very low compared to the other samples.…”

A systematic spectroscopic study of laboratory synthesized manganese oxides relevant to Mars

“…[ 16 ] Thus, the identification of Mn oxide materials remains difficult. [ 7 ] It also has some problems with the x‐ray diffraction (XRD) method to determine the phase of manganese oxides with poor crystallinity. [ 7 ] Spectroscopic techniques provide an alternative tool for analyzing manganese oxides.…”

Mineralogical Characterization of Manganese Oxide Minerals of the Devonian Xialei Manganese Deposit

“…Richmond and Fleischer [20] were the first to separate cryptomelane from a cryptocrystalline aggregate and demonstrated that cryptomelane is characterized by a high mass fraction of K 2 O (3.10-3.88 wt.%). Detailed studies on the crystal structure of natural Mn-K ore (e.g., [2,21,22]) have resulted in the availability of a complete and detailed crystal structure data set. Gao et al [23] studied the chemical composition of cryptomelane from the Xiangtan deposit (Hunan province, South China) with a K 2 O mass fraction of 2.9-3.2 wt.%.…”

“…With regard to pyrolusite, the tunnels are too small to accommodate cations except for possibly H + . Consequently, most natural pyrolusite samples are close to the ideal composition [22], with a K 2 O weight percent of 0.18-0.91 wt.% [25].…”