V. G. Krivovichev

Nomenclature of amphiboles : additions and revisions to the International Mineralogical Association's amphibole nomenclature

The introduction of a fifth amphibole group, the Na-Ca-Mg-Fe-Mn-Li group, defined by 0.50 < B(Mg,Fe2+,Mn2+,Li) < 1.50 and 0.50 ≤ B(Ca,Na) ≤ 1.50 a.f.p.u. (atoms per formula unit), with members whittakerite and ottoliniite, has been required by recent discoveries of B(LiNa) amphiboles. This, and other new discoveries, such as sodicpedrizite (which, here, is changed slightly, but significantly, from the original idealized formula), necessitate amendments to the IMA 1997 definitions of the Mg-Fe-Mn-Li, calcic, sodic-calcic and sodic groups. The discovery of obertiite and the finding of an incompatibility in the IMA 1997 subdivision of the sodic group, requires further amendments within the sodic group. All these changes, which have IMA approval, are summarized.

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: I. Thermodynamic constants at ambient conditions

Understanding and deciphering processes proceeding near the surface are among the urgent tasks of contemporary mineralogy and geochemistry, which are especially important for resolving ecological challenges and developing principles of rational environmental management. The paper presents systematized data published on thermodynamics of minerals (arsenates, sulfates, selenites, and selenates), which are formed in the weathering zone of sulfide ores, and determines approaches to quantitative physicochemical modeling of their formation conditions. Diagrams of phase and chemical equilibria (Eh-pH, diagrams of solubility) of the subsystems of the model system Fe-Cu-Zn-Pb-Co-Ni-As-Se-S-H2O (Fe2+, Fe3+, Cu2+, Zn2+, Pb2+, Ni2+, Co2+, H+//SeO32−, SeO42−, AsO43−, SO42−, OH−-H2O) are used as a thermodynamic basis for modeling mineral-forming processes in the weathering zone of ore deposits. Seventy-two arsenates, about 70 sulfates, and 7 selenites and selenates have been identified in the framework of this system. The available published values of standard thermodynamic functions of the formation of minerals and chemical compounds are given, as well as the Pitzer equation parameters to describe the sulfate systems, which are substantially specific due to the high solubility of their components.

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: IV. Eh-pH diagrams of the Me-Se-H2O systems (Me = Co, Ni, Fe, Cu, Zn, Pb) at 25°C

The behavior of selenium at the Earth’s surface and nearby at low temperatures and pressures is controlled by variations of the redox potential and the acidity of solutions. These parameters determine the migration of selenium and its precipitation as various solid phases. Understanding the mechanism of selenium’s behavior under surface conditions, which is important for solving environmental problems, is an urgent task of contemporary mineralogy and geochemistry. The activities of components in natural waters beyond the zones of natural (oxidation zones) and man-made contamination with selenium (aΣSe = 10−9, aΣFe = 10−5, aΣCu = 10−7, aΣZn = 5 × 10−7, aΣCo = 10−8, aΣNi = 6 × 10−8, aΣPb = 10−8) and in waters formed in the oxidation zone (aΣSe = 10−5–10−4, aΣFe = 10−2, aΣCu = 10−2, aΣZn = 5 × 10−2, aΣCo = 10−3, aΣNi = 10−2, aΣPb = 10−4) have been estimated. Eh-pH diagrams were calculated and plotted using the Geochemist’s Workbench (GMB 7.0) software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 551 particles in solution, 624 solid phases, and 10 gases. The Eh-pH diagrams of the Me-Se-H2O systems (Me = Co, Ni, Fe, Cu, Zn, Pb) were plotted for the average contents of these elements in underground water and for their contents in oxidation zones of sulfide deposits. The formation of Co, Ni, Fe, Cu, Zn, and Pb selenites and selenates at the surface is discussed.

Number of minerals of various chemical elements: Statistics 2012 (a new approach to an old problem)

A list of all mineral species (4809) approved by IMA to 2012 inclusive has been compiled. The crystal chemical formulae of these minerals has been reviewed; each mineral species is marked by a set of the n-component chemical system (where n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). The leading chemical elements by number of mineral species in the Earth’s crust are as follows (number of mineral species is in parentheses): oxygen (3929), hydrogen (2700), silicon (1420), calcium (1130), sulfur (978), aluminum (959), iron (920), sodium (850), copper (588), phosphorus (559), magnesium (547), and arsenic (536). The taxonomy of mineral species is discussed. The important advantage of the proposed systematics is the possibility to range mineral species in strict order, in which each of them would have a unique position. A simple way of ordering minerals opens up possibilities for computer indexing of thermodynamic information. Within each system, minerals are arranged in order of the number of atoms of the first element and, within the group of compounds with the same number of atoms of the first element, in order of the number of atoms of the second element, and so on.

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VI. Solubility of synthetic analogs of ahlfeldite and cobaltomenite at 25°C

The understanding of the mechanisms of the selenium behavior under near-surface conditions is an urgent problem of modern mineralogy and geochemistry, and is very important for solving environmental problems. The objective of this study is to synthesize analogs of ahlfeldite and cobaltomenite and to estimate their solubility in water. These analogs have been synthesized by mixing aqueous solutions of cobalt and nickel nitrates, respectively, and sodium selenite acidified with a solution of nitric acid. The obtained samples have been identified by X-ray diffraction and IR spectroscopy. The solubility has been determined by the isothermal saturation method in ampoules at 25°C, while the solubility products have been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The solubility products of ahlfeldite and cobaltomenite are 10−9.20 and 10−9.44, respectively. The Eh-pH diagrams were calculated and plotted with the GMB 7.0 software package. The Eh-pH diagrams of the Ni-Se-H2O and Co-Se-H2O systems have been calculated for the average contents of these elements in underground water and their contents in acidic water of the oxidation zone of sulfide deposits. The formation of ahlfeldite and cobaltomenite under near-surface conditions is discussed.

The thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VIII. Field of thermal stability of synthetic analog of chalcomenite, its dehydration and dissociation

The objective of this paper is to study the thermal stability of the synthetic analog of chalcomenite, CuSeO3 · 2H2O, and its dehydration and dissociation, in an experimental context. The study has been carried out by a comprehensive application of thermogravimetry (TG), differential scanning calorimetry (DSC), and high-temperature X-ray diffraction at a temperature range of 25–600°C. It has been established that CuSeO3 · 2H2O dehydrates at 202–264°C in three stages corresponding to the formation of intermediate CuSeO3 · 2H2O and CuSeO3 · 1/3H2O hydrate phases. At 480–595°C anhydrous CuSeO3 breaks down into CuO and SeO2 via the formation of a Cu4O(SeO3)3 phase. Enthalpies of the reactions at each stage of the CuSeO3 · 2H2O dehydration and CuSeO3 dissociation have been determined and their kinetic analysis has been carried out.

Thermodynamics of Arsenates, Selenites, and Sulfates in the Oxidation Zone of Sulfide Ores. IX. Physicochemical Formation Conditions and Thermal Stability of Zinc Selenites

The aim of this study is to create a physicochemical analysis of the formation conditions of synthetic zinc selenite, ZnSeO3 · 2H2O and an experimental investigation of its thermal stability, dehydration, and dissociation. This study has been carried out using a comprehensive thermal analysis (thermogravimetry and differential scanning calorimetry) within the temperature interval from 25–600°C. It has been established that ZnSeO3 · 2H2O dehydrates at 81–222°C through four stages corresponding to the formation of intermediate hydrate species: ZnSeO3 · 5/3H2O, ZnSeO3 · H2O, and ZnSeO3 · 1/3H2O. It is suggested that under natural oxidation conditions zinc selenite precipitates as stable (ZnSeO3 · 2H2O) or metastable (ZnSeO3 · H2O) species. Anhydrous ZnSeO3 presumably exists at a higher temperature (up to 479°C) and breaks down within a temperature interval of 479–597°C to form ZnO and SeO2.

A calorimetric and thermodynamic investigation of the synthetic analogs of cobaltomenite, CoSeO3·2H2O, and ahlfeldite, NiSeO3·2H2O

Abstract Thermophysical and thermochemical calorimetric investigations were carried out on synthetic analogs of two minerals: cobaltomenite (CoSeO3·2H2O) and ahlfeldite (NiSeO3·2H2O). The synthesis was realized by mixing of aqueous solutions of cobalt and nickel nitrates, accordingly, and sodium selenite, acidified with the help of a solution of nitric acid and characterized by X-ray powder diffraction and FTIR spectroscopy methods. The low-temperature heat capacities of CoSeO3·2H2O and NiSeO3·2H2O were measured using adiabatic calorimetry between 8 and 340 K, and the third-law entropies were determined. Values of S° (298 K, CoSeO3·2H2O, cr.) = 183.2 ± 1.0 J/(mol·K) and S° (298 K, NiSeO3·2H2O, cr.) = 172.9 ± 1.0 J/(mol·K) are obtained with an uncertainty of 0.5%. The enthalpies of formation for CoSeO3·2H2O and NiSeO3·2H2O were determined by solution calorimetry with H2SO4 solution as the solvent and giving ΔfH° (298 K, CoSeO3·2H2O, cr.) = -1135.3 kJ/mol, ΔfH° (298 K, NiSeO3·2H2O, cr.) = -1133.3 kJ/mol. The Gibbs energy of formation for CoSeO3·2H2O and NiSeO3·2H2O at T = 298 K, 1 atm can be calculated on the basis on ΔfH° and ΔfS°:ΔfG° (298 K, CoSeO3·2H2O, cr.) = -937.4 kJ/mol and ΔfG° (298 K, NiSeO3·2H2O, cr.) = -932.4 kJ/mol. Smoothed CP°(T) values between T = 0 K and T = 320 K for CoSeO3·2H2O (cr.) and NiSeO3·2H2O (cr.) are presented along with values for S° and the functions [H°(T)-H°(0)] and [G°(T)-H°(0)]. These results motivate a re-evaluation of the natural conditions under which selenites, and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The values of ΔfG° for CoSeO3·2H2O and NiSeO3·2H2O were used to calculate the Eh-pH diagrams of the Co-Se-H2O and Ni-Se-H2O systems. These diagrams have been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behavior of selenium, cobalt, and nickel in surface environments have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. Precisely these parameters determine the migration ability of selenium compounds and its precipitation in the form of various solid phases.

Mineral systems and the thermodynamics of selenites and selenates in the oxidation zone of sulfide ores – a review

Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are especially important for resolving ecological challenges and developing principles of good environmental management. Selenium oxysalts, selenites and selenates, are relatively rare as minerals; there are presently only 34 known mineral species. Thirty-one “pure” selenites, which contain only selenite anionic groups, are known to occur naturally. The other three minerals each contain two anionic groups: selenate and selenite (schmiederite), selenate and sulphate (olsacherite), and selenate and iodate (carlosruizite).This work is intended to provide a classification of natural selenium oxysalts based on their chemical composition. Selenites belong to a particular mineral system, whose components are chemical elements required to construct the crystal structure of a mineral (species-defining constituents). The number of components represents the minimum number of independent elements necessary to define the composition of the system. All selenites and selenates are divided into two groups: anhydrous selenites (I) and hydrous selenites and selenates (II).The paper also presents systematized data published on the thermodynamics of selenites, which are formed in the weathering zone of sulfide and selenide ores, and determines approaches to the quantitative physicochemical modeling of formation conditions. The Eh–pH diagrams of the Me–Se–H2O systems (Me = Cu, Co, Ni, Fe, Zn, Ca, Al) were calculated and plotted for the average contents of these elements in aqueous weathering solutions in sulfide deposit oxidation zones.

The thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores. XI. Solubility of synthetic chalcomenite analog and zinc selenite at 25°C

The aim of this study is the synthesis of CuSeO3·2H2O (chalcomenite analog), ZnSeO3·2H2O, and ZnSeO3·H2O and the investigation of their solubility in water. CuSeO3·2H2O has been synthesized from solutions of Cu nitrate and Na selenite, while Zn selenites were synthesized from solutions of Zn nitrate and Na selenite. The samples obtained have been examined with X-ray diffraction and infrared and Raman spectroscopy. The solubility has been determined using the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist’s Workbench (GMB 9.0) software package. Solubility products have been calculated for CuSeO3·2H2O (10–10.63), ZnSeO3·2H2O (10–8.35), and ZnSeO3·H2O (10–7.96). The database used comprises thermodynamic characteristics of 46 elements, 47 base particles, 48 redox pairs, 551 particles in solution, and 624 solid phases. The Eh–pH diagrams of the Zn–Se–H2O and Cu–Se–H2O systems were plotted for the average contents of these elements in underground water in oxidation zones of sulfide deposits.