Abstract
The technogenic mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O from the burned dumps of the Chelyabinsk coal basin have been investigated by single-crystal X-ray diffraction, scanning electron microscopy and high-temperature powder X-ray diffraction. The NH4MgCl3·6H2O phase is monoclinic, space group C2/c, unit cell parameters a = 9.3091(9), b = 9.5353(7), c = 13.2941(12) Å, β = 90.089(8)° and V = 1180.05(18) Å3. The crystal structure of NH4MgCl3·6H2O was refined to R1 = 0.078 (wR2 = 0.185) on the basis of 1678 unique reflections. The (NH4)2Fe3+Cl5·H2O phase is orthorhombic, space group Pnma, unit cell parameters a = 13.725(2), b = 9.9365(16), c = 7.0370(11) Å and V = 959.7(3) Å3. The crystal structure of (NH4)2Fe3+Cl5·H2O was refined to R1 = 0.023 (wR2 = 0.066) on the basis of 2256 unique reflections. NH4MgCl3·6H2O is stable up to 90 °C and then transforms to the less hydrated phase isotypic to β-Rb(MnCl3)(H2O)2 (i.e., NH4MgCl3·2H2O), the latter phase being stable up to 150 °C. (NH4)2Fe3+Cl5·H2O is stable up to 120 °C and then transforms to an X-ray amorphous phase. Hydrogen bonds provide an important linkage between the main structural units and play the key role in determining structural stability and physical properties of the studied phases. The mineral phases NH4MgCl3·6H2O and (NH4)2Fe3+Cl5·H2O are isostructural with natural minerals novograblenovite and kremersite, respectively.
Highlights
The present publication is devoted to the detailed crystal chemical study of NH4MgCl3·6H2O and (NH4) MgCl3 ·6H2 O and (NH4 )2 Fe3+ Cl5 ·H2 O, two ammonium phases from the burned dumps of the Chelyabinsk coal basin (Chelyabinsk Oblast, Russia)
The mineral phase with the chemical composition NH4 MgCl3 ·6H2 O was first described from the Chelyabinsk coal basin as an ammonium analogue of carnallite, KMgCl3 ·6H2 O [18], and named as “redikortsevite” [19], but this naming as well as the mineral species have not been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical
The aim of the present study is to provide the first crystal chemical description of NH4 MgCl3 ·6H2 O and (NH4 )2 Fe3+ Cl5 ·H2 O phases from the Chelyabinsk coal basin, including their first structure refinements and determinations of their stability at increasing temperatures coupled with the calculation of thermal expansion coefficients and their crystal chemical analysis
Summary
The present publication is devoted to the detailed crystal chemical study of NH4 MgCl3 ·6H2 O and (NH4 ) Fe3+ Cl5 ·H2 O, two ammonium phases from the burned dumps of the Chelyabinsk coal basin (Chelyabinsk Oblast, Russia). The same phase was found in a natural environment forming on the surface of basalts of the 2012–2013 Tolbachik effusive eruption (Plosky Tolbachik volcano, Kamchatka area, Far-Eastern Region, Russia) and approved by the CNMNC IMA as a mineral species named novograblenovite (NH4 ,K)MgCl3 ·6H2 O [10]. Another phase studied here is the technogenic analogue of the rare mineral kremersite, (NH4 ,K)2 [Fe3+ Cl5 (H2 O)], that was originally described from Mt. Vesuvius (Somma-Vesuvius Complex, Naples, Campania, Italy) [22]
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