Selenium Minerals: Structural and Chemical Diversity and Complexity

Chemical diversity of minerals containing selenium as an essential element has been analyzed in terms of the concept of mineral systems and the information-based structural and chemical complexity parameters. The study employs data for 123 Se mineral species approved by the International Mineralogical Association as of 25 May 2019. All known selenium minerals belong to seven mineral systems with the number of essential components ranging from one to seven. According to their chemical features, the minerals are subdivided into five groups: Native selenium, oxides, selenides, selenites, and selenates. Statistical analysis shows that there are strong and positive correlations between the chemical and structural complexities (measured as amounts of Shannon information per atom and per formula or unit cell) and the number of different chemical elements in a mineral. Analysis of relations between chemical and structural complexities provides strong evidence that there is an overall trend of increasing structural complexity with the increasing chemical complexity. The average structural complexity for Se minerals is equal to 2.4(1) bits per atom and 101(17) bits per unit cell. The chemical and structural complexities of O-free and O-bearing Se minerals are drastically different with the first group being simpler and the second group more complex. The O-free Se minerals (selenides and native Se) are primary minerals; their formation requires reducing conditions and is due to hydrothermal activity. The O-bearing Se minerals (oxides and oxysalts) form in near-surface environment, including oxidation zones of mineral deposits, evaporites and volcanic fumaroles. From the structural viewpoint, the five most complex Se minerals are marthozite, Cu(UO2)3(SeO3)2O2·8H2O (744.5 bits/cell); mandarinoite, Fe2(SeO3)3·6H2O (640.000 bits/cell); carlosruizite, K6Na4Na6Mg10(SeO4)12(IO3)12·12H2O (629.273 bits/cell); prewittite, KPb1.5ZnCu6O2(SeO3)2Cl10 (498.1 bits/cell); and nicksobolevite, Cu7(SeO3)2O2Cl6 (420.168 bits/cell). The mechanisms responsible for the high structural complexity of these minerals are high hydration states (marthozite and mandarinoite), high topological complexity (marthozite, mandarinoite, carlosruizite, nicksobolevite), high chemical complexity (prewittite and carlosruizite), and the presence of relatively large clusters of atoms (carlosruizite and nicksobolevite). In most cases, selenium itself does not play the crucial role in determining structural complexity (there are structural analogues or close species of marthozite, mandarinoite, and carlosruizite that do not contain Se), except for selenite chlorides, where stability of crystal structures is adjusted by the existence of attractive Se–Cl closed-shell interactions impossible for sulfates or phosphates. Most structurally complex Se minerals originate either from relatively low-temperature hydrothermal environments (as marthozite, mandarinoite, and carlosruizite) or from mild (500–700 °C) anhydrous gaseous environments of volcanic fumaroles (prewittite, nicksobolevite)

Raman spectroscopic characterization of the copper, cobalt, and nickel selenites: Synthetic analogs of chalcomenite, cobaltomenite, and ahlfeldite

<p>Raman spectroscopy has been used to study synthetic analogs of the minerals chalcomenite, cobaltomenite, and ahlfeldite occurring in nature. The results obtained are compared with the spectra of these minerals. In general, the majority of vibrational bands of synthetic species are in good agreement with natural chalcomenite, cobaltomenite, and ahlfeldite. The noticeable discrepancies are found for the bands assigned to the deformation mode of selenite groups. A better signal-to-noise ratio realized with synthetic species aids in comprehensive analysis of the spectra, especially in the region of water bands.</p

A Calorimetric and Thermodynamic Investigation of the Synthetic Analogue of Mandarinoite, Fe₂(SeO₃)₃·5H₂O

Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of mandarinoite. The low-temperature heat capacity of Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) was measured using adiabatic calorimetry between 5.3 and 324.8 K, and the third-law entropy was determined. Using these C p , m o ( T ) data, the third law entropy at T = 298.15 K, S m o , is calculated as 520.1 &#177; 1.1 J∙K&#8722;1∙mol&#8722;1. Smoothed C p , m o ( T ) values between T &#8594; 0 K and 320 K are presented, along with values for S m o and the functions [ H m o ( T ) &#8722; H m o ( 0 ) ] and [ &#934; m o ( T ) &#8722; &#934; m o ( 0 ) ] . The enthalpy of formation of Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) was determined by solution calorimetry with HF solution as the solvent, giving &#916; f H m o ( 298 &nbsp; K , &nbsp; Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O , &nbsp; cr ) = &#8722;3124.6 &#177; 5.3 kJ/mol. The standard Gibbs energy of formation for Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) at T = 298 K can be calculated on the basis on &#916; f H m o ( 298 &nbsp; K ) and &#916; f S m o ( 298 &nbsp; K ) : &#916; f G m o ( 298 &nbsp; K , &nbsp; Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O , &nbsp; cr ) = &#8722;2600.8 &#177; 5.4 kJ/mol. The value of &#916;fGm for Fe2(SeO3)3&#183;5H2O(cr) was used to calculate the Eh&#8315;pH diagram of the Fe&#8315;Se&#8315;H2O system. This diagram has been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behaviors of selenium and iron in the surface environment have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. These parameters precisely determine the migration ability of selenium compounds and its precipitation in the form of solid phases

Multiphase Open Phase Processes Differential Equations

The thermodynamic approach for the description of multiphase open phase processes is developed based on van der Waals equation in the metrics of Gibbs and incomplete Gibbs potentials. Examples of thermodynamic modeling of the multiphase and multicomponent A3B5 systems (In-Ga-As-Sb and In-P-As-Sb) and Na+, K+, Mg2+, Ca2+//Cl&minus;, SO42&minus;-H2O water&ndash;salt system are presented. Topological isomorphism of different type phase diagrams is demonstrated

Non-variant phenomena in heterogeneous systems. New type of solubility diagrams points

The article gives a general classification of non-invariant points in phase equilibrium diagrams of all possible types. The complete topological isomorphism of the diagrams of fusibility, solubility, and liquid-vapor equilibria in various sets of variables is demonstrated. The stability of mono-variant equilibria near the non-variant points is investigated. Recurrent formulas for calculating the number of topological elements of phase diagrams are given. A previously undescribed type of non-invariant points and phase processes in the solubility diagrams is described and characterized. The last ones have no topological analogs in other types of diagrams. Thus, we have carried out, as far as is available to the authors, a complete classification of invariant points and invariant processes in phase equilibrium diagrams of an arbitrary type and with an arbitrary number of components