Tobelite and NH4+-rich muscovite single crystals from Ordovician Armorican sandstones (Brittany, France): Structure and crystal chemistry

Abstract

The crystal structures of tobelite and NH4+-rich muscovite from the sedimentary rocks of the Armorican sandstones (Brittany, France) have been solved for the first time by single crystal X-ray diffraction. The structural study was integrated by electron probe microanalyses, X-ray photoelectron and micro-Fourier transform infrared spectroscopy. The crystals belong to the 2M2 polytype with the following unit-cell parameters: a = 9.024(1), b = 5.2055(6), c = 20.825(3) Å and β = 99.995(8) for tobelite and a = 9.027(1), b = 5.1999(5), c = 20.616(3) Å and β = 100.113(8)° for NH4+-rich muscovite. Structure refinements in the space group C2/c converged at R1 = 8.01%, wR2 = 8.84% and R1 = 5.59%, wR2 = 5.63% for tobelite and NH4+-rich muscovite, respectively. \ud X-ray photoelectron spectroscopy revealed nitrogen environments associated either to inorganic (B.E. 401.31 eV) and to organic (B.E. 398.67 eV) compounds. Infrared spectra showed, in the OH- stretching region (3700-3575 cm-1), two prominent bands, centered at ~ 3629 and ~ 3646 cm-1, and two shoulders at ~ 3664 and ~ 3615 cm-1 which were assigned to Al3+Al3+-OH- arrangements having OH- groups affected by different local configurations. In addition, a series of overlapping bands from about 3500 to 2700 cm-1 characteristic of the NH4+-stretching vibrations, a main band at ~ 1430 and a shoulder at ~ 1460 cm-1 which were associated to the NH4+ bending vibration (ν4) were also present.\ud The ammonium concentration was semi-quantitatively estimated in both crystals from the absorbance of the OH--stretching and NH4+-bending vibrations in the infrared spectra. Additional estimate was obtained for the NH4+-rich muscovite by considering the normalized peak area between K2p3/2 and N1s in the X-ray photoelectron spectrum. The obtained values were also in agreement with those derived from the interlayer spacing in the simulated X-ray powder diffraction spectra. \ud The results of this integrated approach converged to (K0.18Na0.01NH4+0.62)Σ=0.81\ud (Al1.98Fe2+0.02)Σ= 2.00(Si3.19Al0.81)Σ= 4.00O10.00OH2.00 for tobelite and to (K0.46Na0.03Ba0.01NH4+0.36)Σ=0.86\ud (Al1.98Mg0.01Fe2+0.01V3+0.01)Σ=2.01(Si3.13Al0.87)Σ=4.00O10.00F0.08OH1.92 for NH4+-rich muscovite

Synchysite-(Ce) from Cinquevalli (Trento, Italy): Stacking Disorder and the Polytypism of (Ca,REE)-Fluorcarbonates

“…Lepidolite [49]; Illite [50] Polylithionite [51]; Muscovite [52] Nanpingite [53]; Tobelite [54] Synchysite-(Ce) [17] Parisite-(Ce) [18] 2O  180° Anandite [55] Phlogopite [56] Possible, few unit cells observed at the TEM scale (this work, Figure 11).…”

“…Synchysite-(Ce) is characterized by 60° rotations of subsequent bastnäsite portions above the Ca-layers, therefore can be likened to the 2M2 subfamily-B mica polytype, such as lepidolite, for instance. Hypothetical subfamily-A (Ca,REE)-fluorcarbonates, since entailing rotations of 0 or 120° that would align the vertical edges of the CO3 triangles above the heavy atoms columns have, as Lepidolite [49]; Illite [50] Polylithionite [51]; Muscovite [52] Nanpingite [53]; Tobelite [54] Synchysite-(Ce) [17] Parisite-(Ce) [18] 2O ± 180 •…”

A Sb ± Au mineralizing peak at 360 Ma in the Variscan belt

“…3a, 3d). This rather unusual large size permitted a crystallographic characterization of the tobelite species (Mesto et al, 2012;Capitani et al, 2016). The infill of tobelite-bearing quartz veins (up to 10 cm thick) is heterogeneous.…”

“…I site of tobelite grains, from the SADC76 sample, analyzed by electron microprobe. In addition to this, the average of tobelite analyses from Mesto et al (2012) is plotted. 4a, 4b) or crystals that grew between the vein wall and the quartz (Figs.…”

Geo-Agriculture: Reviewing Opportunities through Which the Geosphere Can Help Address Emerging Crop Production Challenges

“…The resulting mineral, tobelite, is the ammonium end-member of muscovite [32]. Extensive ammonium-enriched tobelite deposits have been recorded in many locations including Japan, Europe, China, and the North Sea [32][33][34]. Tobelite offers a potentially viable N fertiliser reserve given its N concentrations are reasonably enriched (Figure 1i).…”