Crystal Chemistry Of Minerals Research Articles

Phosphate geochronometer minerals: Crystal chemistry and radiation disorder, methodological issues of their microprobe non-isotope U–Th–Pb<sub>tot</sub> dating

Research subject. Phosphate mineral geochronometers – the international reference sample of Trebilcock monazite from pegmatites with the age of 272 ± 2 Ma, as well as samples of monazite from pegmatites of the Shartash massif and monazite, cheralite and xenotime from leucogranite of the Peshcherninsky stock and diorite of the Khomutinsky massif, Middle Urals. Methods. The composition of minerals was studied using CAMECA SX100 microprobe; Raman spectra were obtained using LabRAM HR800 Evolution confocal spectrometer. Research aim. Study of the internal texture of the grains of phosphate minerals on the basis of their elemental and spectroscopic mapping; analysis of the mineral crystal chemistry and estimation of auto-irradiation doses; microprobe non-isotopic U–Th–Pbtot dating of phosphate minerals; development of the appropriate algorithm for using analytical techniques. Results. It has been shown that the studied monazites belong to the cerium variety with ThO2 content from 1.1 to 17.2; UO2 – from 0 to 0.8; PbO – from 0.01 to 0.23 wt % (detection limits 160, 230, and 110 ppm). When analyzing the PbO content, the background line was interpolated into models of linear background (Trebilcock monazite, monazite and cheralite of the Peshcherninsky stock) and exponential background (monazite of the Shartash massif). It has been shown that for monazite, both huttonite and cheralite types of isomorphism are realized; the non-stoichiometric parameter of its composition β = (Si + Ca)/(Th + U + Pb + S) lies in the range of 0.95–1.05, which indicates the preservation of the U–Th–Pb-system. The analysis of BSE-images, intensity distribution maps of the Th Mα and Pb Mα RE lines, compositional point analyses and the results of spectroscopic mapping of the parameters of the ν1(PO4) vibrational mode testify to high homogeneity of Trebilcock monazite and pronounced zoning of the Ural monazites. It has been shown that the parameters of the ν1(PO4) vibrational mode in monazites are determined by the superposition of two factors, i.e. chemical and radiation disorder. The data on U, Th, and Pb content for different zones of monazite grains were used to perform non-isotopic U–Th–Pbtot dating: weighted average age values for the zones were obtained, and isochron plotting was made on the ThO2* vs. PbO diagram. The datings obtained based on the Trebilcock sample are in satisfactory agreement with the literature. Conclusions. The dating of monazite from leucogranite of the Peshcherninsky stock and the Shartash massif are in agreement with the U-Pb isotopic dating of zircon. The physical and chemical characteristics of cheralite, xenotime, and zircon in samples from the Peshcherninsky stock were analyzed. The U–Th–Pbtot dating of cheralite, xenotime, and zircon was attempted. The described algorithm and analytical methods were used at the Geoanalitik Common Use Center for microprobe non-isotopic dating of phosphate minerals.

Spinel in planetary systems

Spinel is ubiquitous as a rock-forming mineral in terrestrial, lunar, and planetary basalts and closely associated meteoritic equivalents. A major unknown is whether these rocks formed under similar conditions of partial melting of primary or modified mantle, whether redox environments played a role in evolutionary trends, and did mineral crystal chemistry have any influence on elemental partition between solids and liquids? In a novel approach by Papike et al. (2015), spinel is used as an informative, albeit complex indicator of oxygen fugacity, site occupancy of multiple valence elements, and spinel structural types. Planetary basalts may be reduced (IW-3), oxidized (Earth at FMQ), or of intermediate redox state (Mars). Taking an expansive view, the spinel approach holds enormous promise in understanding the magmatic differentiation of asteroids.

X-ray diffraction and the development of the mineral crystal chemistry

After the epochal experience of Friedrich and Knipping suggested and interpreted by Laue, the scene rapidly moved to England where the young Bragg correctly explained the results of the Munich discovery and showed how to use X-rays to determine the arrangement of atoms in crystals and, in few years, actually derived the structures of several inorganic compounds. Their comparison permitted Bragg to assert that crystals are composed of “inelastic spheres in contact” and that “it is possible to assign to the sphere representing an atom… a constant diameter.” The development of these concepts by various authors (Wasastjerna, Goldschmidt, …) led to the well-known Table of ionic radii by Pauling, who—at the same time—proposed the rules for the stability of ionic compounds, based on the concept of coordination polyhedra as building elementary modules of inorganic compounds. The stability rules of Pauling, as well as the conception, formulated by Bragg, of the structures of complex oxides as characterized by ‘close packing’ of oxygen anions, were the main guiding lines in the ‘trial and error’ procedures to determine the atomic arrangements in minerals and in inorganic compounds in general. The increasing number of known structures raised the need for proper classification schemes, largely based on elementary structural units (as the silicon tetrahedra in silicates) and the various ways of their connection. At the same time the wide basis of structural data and the increased precision and accuracy of those data stimulated the revision of the old compilations of ionic radii as well as a re-formulation of the Pauling’s rule of valence-bond balance. Examples are presented of the application of the crystal chemical concepts to some important mineralogical, geochemical and geophysical problems. An explosive growth of structural knowledge in the last decades of the twentieth century was stimulated by the new techniques of data collection, the high speed of computing and the advent of direct methods of structure solution, which resulted not only in an enormous increase in the number of known structures, but also in unraveling very complex arrangements. This increasing structural knowledge accompanied and stimulated the development of a new way to look at the arrangements of inorganic compounds, based on their modular aspects. The concept of assembling different, geometrically compatible modules, mainly structural layers, to build up complex structures has been very productive; in fact it not only consented a deep knowledge of the structural relationships inside wide families of natural and synthetic compounds, but also favored the solution of complex structural problems and permitted careful previsions of new possible structural arrangements. Few lines of future developments of the crystal chemical study of minerals are briefly presented and discussed: ‘synergy’ between mineralogists and material chemists; computational simulations of structural arrangements; new experimental approach through automated electron diffraction tomography.

Crystal structure of nanlingite the first mineral with a [Fe(AsO3)6] configuration

Nanlingite was first described as a new mineral from a dolomitic limestone along a contact between greisenized granite and dolomitic limestone in the Nanling area, Hunan Province, China. The structure was solved and refined on single-crystal X-ray data in space group R 3 m , with a = 10.2114(10), c = 25.689(3) A, V = 2319.2(6) A 3 , to R1 = 0.021, wR2 = 0.049. The chemical formula of nanlingite is Na(Ca, Li, Na) 6 (Mg, Fe) 12 (AsO 3 ) 2 [Fe(AsO 3 ) 6 ] F 14 with Z = 3 according to the crystal structure refinement. The complex framework is formed by edge- and corner-sharing of distorted NaF 8 and CaF 4 O 4 cubes, MgF 2 O 4 octahedra, and AsO 3 trigonal pyramids. The lithium atom occupies (22 %) the split site at 0.58(2) A from the main Ca site and exhibits a five-fold coordination with 2.21 A. The iron atom (at 3 b , site symmetry 3m) is surrounded by six As atoms of AsO 3 groups at a distance of 2.40 A with the lone-pair electrons pointing towards the central atom. This [Fe(AsO 3 ) 6 ] cluster is a novel configuration in the crystal chemistry of minerals. According to Mossbauer spectra and electron energy-loss spectroscopy data the oxidation state of Fe in nanlingite is mainly Fe II with a low-spin state. In the configuration of arsenite groups, the distance = 1.73 A of the [Fe(AsO 3 ) 6 ] clusters is shorter than the normal range. The empirical crystal-chemical formula for nanlingite is (Na 0.90 Li 0.10 )∑ 1.00 (Ca 4.41 Li 1.06 Mg 0.17 Na 0.06 Mn 0.05 □ 0.25 )∑ 6.00 (Mg 11.38 Fe 3+ 0.30 Al 0.29 Ti 0.03 )∑ 12.00 (AsO 3 ) 2 [Fe II (AsO 3 ) 6 ](F 13.77 OH 0.16 )∑ 13.93 .

Evaluation of soils of the Vladimir opolie on the basis of the content of minerals carrying plant nutrient elements

On the basis of a differentiated analysis of a number of elements and crystal chemistry of minerals in fractions with a size < 1, 1–5, and 5–10 µm, data are obtained on reserves of plant nutrient elements in agrogray heavy loam soils of Vladimir opolie.

PERTLIKITE, A NEW TETRAGONAL Mg-RICH MEMBER OF THE VOLTAITE GROUP FROM MADENI ZAKH, IRAN

Pertlikite, a new member of the voltaite group, is the tetragonal Mg-dominant analogue of the isometric phases voltaite and zincovoltaite. At its type locality, Madeni Zakh, Iran, the mineral occurs in a pyrite-bearing trachytic eruptive rock, and probably formed after the decomposition of pyrite. Pertlikite forms single crystals up to 1 cm; the phase is associated with metavoltine, botryogen, pyrite and alunite. In contrast to voltaite and zincovoltaite, the optical properties and the single-crystal study of the structure ( R 1 = 0.022) confirm the tetragonal symmetry, ω = 1.590(2), e = 1.586(2), space group I 4 1 / acd , a 19.2080(3), c 27.2158(7) A, V 10041.2(6) A 3 , and Z = 8. The results of the chemical analysis, in combination with the Mossbauer data and the crystal-structure refinement, give the formula (K 1.98 Na 0.01 ) ∑1.99 M 2 (Fe 2+ 1.13 Mg 0.49 Mn 2+ 0.27 Fe 3+ 0.10 Zn 0.01 ) ∑2.00 M 3 (Mg 2.52 Fe 3+ 1.49 ) ∑4.01 M 1 Fe 3+ 2.00 Al 1.00 (SO 4 ) 12.00 ·18 H 2 O, which can be simplified to an ideal formula: K 2 M 2 (Fe 2+ ,Mg) 2 M 3 (Mg,Fe 3+ ) 4 M 1 Fe 3+ 2 Al (SO 4 ) 12 ·18 H 2 O. The strongest eight lines of the powder pattern [ d in A( I )( hkl )] are: 5.543(28)(132), 3.396(100)(440), 3.136(21) (345), 3.038(39)(444), 2.848(31)(361), 2.534(21)(273), 2.078(29)(567) and 1.601(21)(6104). The unit-cell parameters refined from the powder data (Cu K α radiation) are a 19.2167(2), c 27.1976(4) A. The tetragonal structure of pertlikite results from Mg,Fe order at the Fe 2 site. Relative to the isometric voltaite and zincovoltaite, the Fe 2 site splits to create a site that is predominantly Mg ( Mg 3) and another that is dominantly Fe ( Fe 2) in pertlikite. For the three metal sites, the results of the refinement are Fe 1: . Fe; Fe 2: Fe >> Mg; Mg 3: Mg >> Fe. The H 2 O molecules that bond to the Al atom are extensively disordered, as has been observed in the isometric phases. The measured density is 2.59(3) g/cm 3 (by pycnometer), and the calculated density is 2.56(1) g/cm 3 . The name honors Franz Pertlik, Professor of Mineralogy and Crystallography, University of Vienna, Austria, in recognition of his extensive work on the crystal chemistry of minerals.

Physicochemical properties of talc ore from Pout-Kelle and Memel deposits (central Cameroon)

AbstractPhysicochemical properties of representative samples from talc deposits discovered at Pout-Kelle and Memel in Cameroon have been investigated using a variety of techniques. The data allow the study of the mineral crystal-chemistry, chemical and modal compositions, grain size distribution, textures and surface heterogeneity, and morphometric characteristics. As a result, we found that talc (platy or round, Fe-rich) prevails (65–90%) over Cr-chlorite (7–26%), halloysite, chromite, rutile, brucite and magnesite. Chemically, talc ores are made up of SiO2, MgO, Fe2O3 and minor Al2O3. Mode values range from 50 to 55 μm at Memel and from 30 to 90 μm at Pout-Kelle. Specific surface areas measured by BET and t-plot methods range from 1.3 to 2.5 m2/g. The large values of morphometric characteristics are indicative of high crystallinity and platiness. Potential uses of these talc ores in the rubber, plastics and paper industries require beneficiation processes. Interestingly, the Memel deposit and most zones of the Pout-Kelle deposit are free of needle-shaped crystals, an advantage for environmental safety.

Bonded interactions and the crystal chemistry of minerals: a review

Connections established during last century between bond length, radii, bond strength, bond valence and crystal and molecular chemistry are briefly reviewed followed by a survey of the physical properties of the electron density distributions for a variety of minerals and representative molecules, recently generated with first-principles local energy density quantum mechanical methods. The structures for several minerals, geometry-optimized at zero pressure and at a variety of pressures were found to agree with the experimental structures within a few percent. The experimental Si–O bond lengths and the Si–O–Si angle, the Si–O bond energy and the bond critical point properties for crystal quartz are comparable with those calculated for the H6Si2O7 disilicic acid molecule, an indication that the bonded interactions in silica are largely short ranged and local in nature. The topology of model experimental electron density distributions for first and second row metal M atoms bonded to O, determined with high resolution and high energy synchrotron single crystal X-ray diffraction data are compared with the topology of theoretical distributions calculated with first principles methods. As the electron density is progressively accumulated between pairs of bonded atoms, the distributions show that the nuclei are progressively shielded as the bond lengths and the bonded radii of the atoms decrease. Concomitant with the decrease in the M–O bond lengths, the local kinetic energy, G( r c), the local potential energy, V( r c), and the electronic energy density, H( r c) = G( r c) + V( r c), evaluated at the bond critical points, r c, each increases in magnitude with the local potential energy dominating the kinetic energy density in the internuclear region for intermediate and shared interactions. The shorter the bonds, the more negative the local electronic energy density, the greater the stabilization and the greater the shared character of the intermediate and shared bonded interactions. In contrast, the local kinetic energy density increases with decreasing bond length for closed shell interactions with G( r c) dominating V( r c) in the internuclear region, typical of an ionic bond. ...

Hole defects in the crystal structure of synthetic lipscombite (Fe 4.7 3+ Fe 2.3 2+ )[PO4]4O2.7(OH)1.3 and genetic crystal chemistry of minerals of the lipscombite-barbosalite series

The crystal structure of a synthetic analog of the mineral lipscombite (Fe2.32+Fe4.73+)[PO4]4O2.7(OH)1.3 obtained under hydrothermal conditions in the LiF-Fe2O3-(NH4)2HPO4-H2O system is resolved (R = 0.040) by X-ray diffraction analysis (Bruker Smart diffractometer with a highly sensitive CCD detector, MoKα radiation): a = 14.776(3) A, b = 14.959(3) A, c = 7.394(1) A, β = 119.188(4)°, sp. gr. C2/c, Z = 4, ρexp = 3.8 g/cm3, ρcalcd = 3.9 g/cm3. Fe2+ and Fe3+ cations are statistically distributed in each of four crystallographically independent positions, while occupying the corresponding octahedra with probabilities of 60, 90, 100, and 91%. The ratio Fe2+/Fe3+ in the composition of the crystals was established by Mossbauer spectroscopy. Lipscombite is interpreted as a mineral of variable composition described by the formula (Fex2+Fen−x3+)[PO4]4Oy(OH)4−y. The field of stability is determined as a function of the iron content and the ratio Fe2+/Fe3+. It is shown that at n = 6 iron cations are ordered in octahedra and barbosalite structure is formed. An interpretation of genetically and structurally related members of the lipscombite family within a unified polysomatic series is proposed.

Interaction between aqueous chromium solutions and layer silicates

The interactions between Cr in aqueous solutions and phyllosilicates were studied to determine: (a) the amount of Cr(VI) to Cr(III) reduction in aqueous solutions by Fe(II)-bearing phyllosilicates; (b) the removal of the Cr species from solution by interaction with phyllosilicates, as a function of Cr(III) concentration and anionic environment. Chlorite, corrensite and montmorillonite were reacted with solutions containing Cr(VI) (1.62×10 −3 N, 5.77×10 −3 N and 1.32×10 −1 N, respectively). The sorption/desorption of Cr(III) by saponite was investigated in different anionic environments (Cl −, NO − 3 and CH 3COO −) and at different initial Cr(III) concentrations (3.21×10 −3 N, 5.49×10 −3 N and 8.49×10 −3 N). The extent of Cr(VI) reduction and the amount of Cr removed by phyllosilicates were measured by analysis of the liquid portion separated by centrifugation after controled periods of exposure. The minerals were studied by chemical, thermal and X-ray powder diffraction analyses. The results show that: (i) Fe(II)-bearing phyllosilicates sorb Cr and reduce Cr(VI) to Cr(III); (ii) the extent of reduction depends on the solution concentration and on mineral crystal chemistry; (iii) Cr(III) sorption isotherms show that the degree of uptake depends both on the initial concentration of metal in solution and on the anionic environment, the order of effectiveness being Cl −≅NO − 3>CH 3COO −; (iii) Cr(III) is retained in the mineral substrate and its release is difficult.

Interaction between montmorillonite and pollutants from industrial waste-waters: exchange of Zn 2+ and Pb 2+ from aqueous solutions

The interactions between montmorillonite (sample SAz-1 from the Source Clay Repository of the Clay Minerals Society) and Zn 2+ and Pb 2+ solutions of different ionic strengths (from about 10 −5 to 1 M) are studied in order to observe changes in the clay-solution system and mineral crystal chemistry. In both types of solution the stationary state of exchange, attained within 20 min, depends on the solution's ionic strength. The uptake can be interpreted by means of a Langmuir-type equation with Zn 2+ somewhat more easily exchanged than Pb 2+. The shifting of the d (001) spacing from 15.3 Å (natural sample) to 12.8 Å (Zn 2+-exchanged montmorillonite) and 12.4 Å (Pb 2+-exchanged montmorillonite) suggests that the kind of interlayer cation affects the c dimension of the layer. Upon heating, the exchanged montmorillonite layer collapses ( d (001),Zn = 9.5 Å; d (001),Pb = 10.0 Å) and the closest packing is attained at T = 200°C for Pb 2+ - and at 380°C for Zn 2+-exchanged samples. In addition to reactions observed for natural and Pb 2+-exchanged samples in the temperature ranges 20–250°C and 500–700°C, the thermal analyses of Zn 2+-exchanged montmorillonite show a reaction at about 380°C which can be related either to strongly bonded water molecules or to “brucitic-like” interlayers or to Zn 2+-exchanged octahedra.

鉱物結晶化学における２，３の課題

Recent developments in crystal chemistry of minerals are reviewed and several problems are suggested to be investigated as extensions of the presented accomplishments. Electron-density distributions in inorganic crystals have been extensively investigated for these twenty years, and valuable information has been obtained on electronic states of crystals with simple structures. It is supposed to be most promising for more complex crystals to collect diffraction data with extremely small single-crystals by making use of intense X-rays of SR. Single-crystal X-ray diffraction data afford not only electron-density distributions, but also anharmonic thermal parameters for atoms in the crystals. The knowledge on anharmonic thermal vibrations obtained at various temperatures and pressures might be useful to check the varidity of the interatomic potentials assumed in molecular dynamics calculations for simulating the states of materials in the Earth's interior. Consideration of anharmonic thermal vibrations is also important to get correct positional parameters of atoms. In the case of LiTaO3, the z parameter of Ta shifted by 0.066 A relative to Li and O on introduction of anharmonic thermal parameters into the parameters to be refined in the least-squares calculations. The author and his collaborators succeeded to grow a low temperature form crystal of BaB2O4 at a temperature above the phase-transition point from a supercooled melt of pure BaB2O4. A similar crystal growth of a low temperature form is expected for rock-forming silicate minerals, since silicate melts are easily supercooled.

Mechanical behavior of magma reservoir envelopes: Elasticity of the olivine tholeiite solidus

A study of the elasticity of the solidus of igneous rocks provides a means of evaluating several high temperature mechanical characteristics of the zone that forms the transition region between solid rock and rock with a small fraction of partial melt — that is, the magma reservoirenvelope. This type of study has been performed for Hawaiian olivine tholeiite, by employing the theoretical treatment ofWalsh (1969). The effective aggregate bulk modulus (K*), aggregate rigidity (μ*), aggregate Young’s modulus (E*) and the aggregate Poisson’s ratio (n*) have been used to characterize the range in elastic behavior expected for this partially molten envelope. The details of mineralogy, mineral crystal chemistry and microstructure for a tholeiitic basalt from a deep-ponded flow unit (the Boiling Pots), as well as the geometry of melt pocket aspect ratios have been used to provide a basis for computing the elasticity for a shallow reservoir solidus. For a broad range in modal mineralogy, the internal 0–1% melt represents a transition region from an aggregate elasticity controlled by mineral composition, to an elastic behavior dominated by the melt phase (evaluated at a melt pocket aspect ratio ofe=0.001). For vesicular rocks in a low pressure environment, the internal 0–1% melt represents a transition from porosity-controlled elasticity to melt-controlled elasticity, evaluated at a prevalent aspect ratio ofe=0.001, and over the porosity range Φ=0.0−0.20 (20%). Thin melt films found to separate plagioclase microlites (0.0001=e) are capable of effecting a 94.7% reduction in Young’s modulus, E*, over the 0–1% melt range, and suggest that the reservoir envelope may be critically weakened by rather small volume fractions of liquid, if dispersed in such narrow packets.