High-Pressure Synthesis, Synchrotron Single-Crystal XRD and Raman Spectroscopy of Synthetic K–Ba Minerals of Magnetoplumbite, Crichtonite and Hollandite Group Indicatory of Mantle Metasomatism

“The paper summarizes the results of an experimental study of the formation of K–Ba high-Ti (and Cr) oxides synthesized in the chromite–rutile/ilmenite–K2CO3/BaCO3–H2O–CO2 systems at 1.8–5.0 GPa. Experiments confirm the conclusion that the formation of K–Ba high-Ti oxides characterizes the most advanced or repeated metasomatic stages in upper mantle peridotites, which lead first to the formation of simple Ti oxides and then to the formation of K–Ba high-Ti and Cr oxides. Relations between the oxides is a function of the activity of the K and Ba components in the fluid. The appearance of priderite corresponds to the highest activity of K in the mineral-forming media. Redledgeite is formed only in the Fe-poor chromite–rutile–H2O–CO2–BaCO3 system, and, in the system with ilmenite, minerals of the magnetoplumbite group preferably crystallize. A direct dependence of the Cr content in oxides on pressure is revealed. Raman spectra of K–Ba high-titanium oxides are presented. The structure of a potassium compound of a magnetoplumbite group with the chemical formula K0.90Ti5.16Cr2.94Fe2.54Mg0.87Al0.22Mn0.30O19 is studied by single-crystal X-ray diffraction using a synchrotron radiation. The obtained data can be used to specify the nomenclature of the magnetoplumbite mineral group.”

2.2.2. Raman Spectroscopy

To obtain the Raman spectra, the Senterra (Bruker) microscope/spectrometer equipped with DPSS laser 532 nm and also the Renishaw RM1000 microscope/spectrometer equipped with the diode-pumped modular laser 532 nm (for barium oxides) were used. The typical parameters of the experiment were as follows: output power 20 mW, slit 50 × 100 mm, accumulation time 200 s (for potassium oxides) and laser output power 22 mW, slit 50 mm, accumulation time 100 s (for barium oxides). The baselining procedure was applied to the spectra. The alignment of the spectrometer was checked before being run by taking spectra on high-purity monocrystalline Si. The measured spectra were processed using Fityk 1.3.1. software ( (accessed on 01 February 2023)).

3.3. Raman Spectra of Synthetic K–Ba High-Titanium Oxides

Raman spectra of the synthesized minerals were obtained in the range of 160–1000 cm−1. Raman spectra of yimengite and hawthorneite, priderite and redledgeite and mathiasite and lindsleyite had a similar topology.

3.3.1. Phases of the Crichtonite Group

The Raman spectra of mathiasite and lindsleyite had several peaks (Figure 5); the strongest peak appeared at 685–687 cm−1 and had shoulders from both sides.
Figure 5. Raman spectrum of synthetic lindsleyite and mathiasite, processed using the Fityk program.
The peaks next in intensity were at 377 and 386 cm−1, 262 and 274 cm−1, 223 and 221 cm−1 and 180 and 177 cm−1 for mathiasite and lindsleyite, respectively. The spectrum of mathiasite had addition bands at 334 and 451 cm−1.
For comparison, the Raman spectra of mathiasite and lindsleyite synthesized from oxides [13] differed in a lower Fe content. Variations in the position of all lines of the spectra shown within 5–10 cm−1 can be explained by variations in the contents of Ca, Fe and Ti in the composition of the minerals of the crichtonite group.

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