Sector zoned aegirine from the Ilímaussaq alkaline intrusion,South Greenland

Sector zoned aegirine crystals occur in the interstices of peralkaline nepheline syenites in Ilímaussaq. The crystals have grass-green [001] sectors enriched in Ca and Fe²⁺ (as CaFeSi₂O₆), Mn and Zr; pale green {010} sectors enriched in Al (as NaAlSi₂O₆); blue-green {110} sectors enriched in Ti (as NaTi_0.5Fe _0.5 ²⁺ Si₂O₆); and light green {100} sectors enriched in Fe₃₊ (as NaFe³⁺ Si₂O₆).The crystals grew in the liquid with a rate that did not exceed the diffusion rate of most elements in the liquid. However. Fe³⁺ seems to have had diffusion rates lower than the crystal growth rate, and this probably caused the development of some sectors enriched in acmite and others enriched in the hedenbergite component. For Al, Ti and Zr a crystal structural control is envisaged although a recent structure-based model for sector zoning fails to explain the efficient separation of these elements into different sectors.Three more occurrences of sector zoned aegirine are noted, all from peralkaline nepheline syenites. The phenomenon is probably more widespread than hitherto realised.Contribution to the mineralogy of Ilímaussaq no. 62     

A thermochemical study of the distribution of cobalt and nickel between diopsidic pyroxene and melt

Glasses and crystals of compositions MgCaSi₂O₆, CoCaSi₂O₆ and NiCaSi₂O₆ were studied by high temperature solution calorimetry, x-ray diffraction, and pycnometry. These data were combined with trace element distribution data to obtain values for ΔAG⁰, ΔH⁰, ΔS⁰, and ΔV⁰ for M-Mg exchange reactions. Enthalpies of vitrification increase in the order Co, Mg, Ni as do volumes of vitrification and apparent melting points. The mixing of Co and Mg, Ni and Mg, and Co and Ni is almost ideal in crystals and glasses, with small negative heats of mixing and small volume changes. The exchange reactions MgCaSi₂O₆ (xl) + MCaSi₂O₆ (liq) = MgCaSi₂O₆ (liq) + MCaSi₂O₆ (xl) are exothermic for Ni and endothermic for Co. The volumes and entropies of the exchange reaction are small.     

EPR study of coordination of Ag and Pb cations in BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals and barium borate glasses

It is shown the possibility to determine the coordination of paramagnetic ions in disordered solid structures, e.g., in barium borate glasses. For this purpose the electron paramagnetic resonance (EPR) method was used to study α-and β-BaB₂O₄ crystals and glasses of 45·BaO × 55·B₂O₃ and 40·BaO × 60·B₂O₃ (mol%) composition activated by Ag⁺ and Pb²⁺ ions. After the samples were exposed to X-rays at 77 K, different EPR centers were observed in them. In α-and β-BaB₂O₄ crystals and glasses the EPR centers Ag²⁺, Ag⁰, Pb⁺, Pb³⁺, and hole centers of O⁻ type were studied. The EPR parameters of these centers and their arrangement in crystal structure were determined. It is shown that Pb³⁺ ions in β-BaB₂O₄ crystals occupy Ba²⁺ position in an irregular polyhedron from the eight oxygen, whereas in α-BaB₂O₄ crystals they occupy Bа₂ position in a sixfold coordination. Pb⁺ ions in α-BaB₂O₄ crystals occupy Bа₁ position in a ninefold coordination from oxygen. In barium borate glasses, Pb³⁺ ions were studied in coordination polyhedron from six oxygen atoms and in a polyhedron from nine to ten oxygen atoms. It is assumed that the established difference in the structural position of Pb³⁺ ions in glasses is due to their previous incorporation in associative cation–anion complexes (AC) and “free” structure-forming cations (FC). Computer simulations have been performed to analyze the stability of specific associative complexes and to compare their bond lengths with experimental data.     

Chemical composition and species attribution of tourmalines from a rare-metal pegmatite vein with scapolite, Sangilen Upland, Tuva

A detailed study of the chemical composition and substitutions in calcium tourmalines from a scapolite-bearing rare-metal pegmatite vein from the Sol’bel’der River basin has shown that their species attribution is determined by occupancy of octahedral site Y. The composition of the yellow tourmaline most abundant in the central part of the pegmatite bodyis rather constant and characterized by the ideal formula Ca(Mg₂Li)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F. Variations in the chemical composition of zonal tourmaline crystals from the contact part of the pegmatite are controlled by abrupt change in the chemical medium during their formation. The yellow cores of these crystals are close in composition to tourmaline from the central part of the pegmatite vein. The Mg content abruptly decreases toward the crystal margin: Mg²⁺ → Fe²⁺, 2Mg²⁺ → Li⁺ + Al³⁺, and Mg²⁺ + OH → Al³⁺ + O²⁻. The composition of dark green marginal zones in tourmaline is characterized by the ideal formula Ca(Al_1.5Li_1.5)Al₆(Si₆O₁₈)(BO₃)₃ (OH₂O)(F). The results indicate specific formation conditions of pegmatite. The crystallochemical formulas of the studied tourmalines allow us to regard them as new mineral species in the tourmaline group.     

Titanium substitution and OH-bearing defects in hydrothermally grown pyrope crystals

A series of Ti-substituted pyrope crystals was synthesized in the system MgO-(Na₂O)-Al₂O₃-TiO₂-SiO₂-H₂O at P_H20 = P_tot between 25 and 30 kbars and 975 and 1000° C, using graphite heated piston-cylinder devices. The crystals, ranging up to 500 m in diameter, were studied by X-ray, electron-microprobe and FTIR-microscope spectrometric techniques. The pyrope crystals were colourless when hem/mt or mt/wu buffers were used during the synthesis, and pale blue with the wu/iron buffer and in unbuffered runs. Sodium was not found in the synthetic crystals, titanium was always near 0.06 Ti atoms pfu, independent on the Ti-excess used in the starting material. A substitution Al_2+[6]+Si_4+[4]+4O_2-= Ti_4+[6]+_[4]+[(OH)₃O^^5-, providing charge balance for octahedral Ti⁴⁺-substitution is found to be compatible with all properties (number, widths, position, integrated intensity) of the stretching vibrations of defect hydroxyls, which have energies 3684, 3568, 3525 cm^-1.This work was made possible through a research fellowship, generously provided by the Alexander von Humboldt-Stiftung, Bonn, Bad Godesberg, to V.M.K.     

Influence of oxygen partial pressure on the Mg/Fe distribution in olivines

The dependence of Mg/Fe ordering on oxygen partial pressure in natural olivine crystals of volcanic origin has been studied by X-ray diffraction. Two natural crystals with 10% and 12% fayalite have been investigated and the atomic positions, anisotropic temperature factors, extinction coefficients and site occupancies have been refined, reaching R-values of 2.2%. After subjecting the crystals to oxygen partial pressures of 10^?16 bar and 10^?21 bar the crystals were studied again. In total six crystals were studied and the distribution coefficients K _D determined. The natural untreated crystals had K _D=1.09 and 1.06, e.g., a slight preference of Fe in (M1). p(O₂) of 10^?16 bar increased the ordering of Fe in (M1) to K _D=1.2, while p(O₂)=10^?21 bar reversed K _D to 0.8 with ordering of Fe in (M2). These experiments suggest that Mg/Fe ordering in olivines is primarily determined by the prevailing oxygen partial pressure.     

Zn-rich högbomite formed from gahnite in the metabauxites of the Menderes Massif,SW Turkey

Gahnite, ZnAl₂O₄, present as an accessory mineral in regionally metamorphosed low-grade diasporites, has reacted in adjacent higher-grade, corundum-bearing metabauxite equivalents (emeries) to form Zn-rich högbomite, (Zn,Fe²⁺,Mg,Ni)_t-2x (Ti,Sn)_xAl₂O₄, of the 4H polytype. Commonly, the initial högbomite crystals grew epitactically along the octahedral faces of gahnite, which was subsequently dissolved, so that högbomite now forms spectacularly intergrown sets of eight crystals in perfect crystallographic orientation to each other. This indicates a metamorphic reaction, probably involving a fluid, transporting mainly the elements Zn and Al. Reactant Ti minerals in the diasporites were rutile and titanian hematite (10–15 mol% FeTiO₃). In the emeries högbomite coexists with still more Ti-rich hematites containing between 26 and 37 mol% FeTiO₃. The overall reaction relations involving partial reduction may be subdivided into the intial univariant reaction, gahnite+diaspore+Ti-hematite+rutile=högbomite+H₂O+O₂. This was followed, in the absence of gahnite, by compositional readjustments of högbomite and Ti-hematite and the appearance of magnetite. Core to rim zoning profiles indicate that, with continued growth, the högbomite crystals became poorer in Zn and Ti, but richer in Fe²⁺, while the Ti-contents of coexisting hematite increased. Högbomite formation at the expense of gahnite started at temperatures as low as about 400° C for an estimated pressure of 5–6 kbar.     

Structural changes in the FeAl2O4–FeCr2O4 solid solution series and their consequences on natural Cr-bearing spinels

The influence of Al–Cr substitution on the spinel structure was studied in synthetic single crystals belonging to the FeCr₂O₄–FeAl₂O₄ series produced by flux growth at 1,000–1,300 °C in controlled atmosphere. Samples were characterized by single-crystal X-ray diffraction, electron microprobe analyses and Mössbauer spectroscopy. Crystals of sufficient size and quality for single-crystal X-ray diffraction were obtained in the ranges Chr_0–0.45 and Chr_70–100 but not for intermediate compositions, possibly due to a reduced stability in this range. The increase in chromite component leads to an increase in the cell edge from 8.1534 (6) to 8.3672 (1) Å and a decrease in the u parameter from 0.2645 (2) to 0.2628 (1). Chemical analyses show that Fe²⁺ is very close to 1 apfu (0.994–1.007), Al is in the range 0.0793–1.981 apfu, Cr between 0 and 1.925 apfu. In some cases, Fe³⁺ is present in amounts up to 0.031 apfu. Spinels with intermediate Cr content (Chr component between 40 and 60) are strongly zoned with Cr-rich cores and Cr-poor rims. Mössbauer analyses on powdered spinels of the runs from which single crystal has been used for X-ray structural data show values of Fe³⁺/Fe_tot consistently larger than that calculated by EMPA on single crystals, presumably due to chemical variation between single crystals from the same runs. The synthesis runs ended at a temperature of 1,000 °C, but it is possible that cation ordering continued in the Cr-poor samples towards lower temperatures, possibly down to 700 °C.     

Synthese et etude morphologique,radiocristallographique et spectrometrique I.R. de la wadeite K2 ZrSi3 O9; domaine de formation; remplacements isomorphiques; application a la geochimie du zirconium

The first synthesis of wadeite, K₂ZrSi₃O₉, was realised by the authors in 1970 using a hydrothermal technique. These new data were the basis for further research works about the formation of this mineral by way of dry and hydrothermal synthesis, making use of various potassic compounds. The conditions for the formation of wadeite were explained as a function of the chemical environment. The pressure—temperature range of formation was investigated from 100 to 900°C and 100 to 2000 bar. The morphology of the wadeite crystals that were obtained is discussed. Starting from wadeite structure, various isomorphic substitutions were determined (Zr/Hf; K/Rb, Cs; Si/Ge); their study resulted in an interesting diagram of crystallographic parameters as a function of the ionic radius of the substituted alkaline elements: cryst. param. = f(R⁺_{alk. element}); the bands are linear. The infra-red investigations enabled us to establish the spectrum of (Si₃O₉)^6? and (Ge₃O₉)^6? in wadeite structure as well as the substitutions caused by alkalis and transition metals. Finally a comparative experimental investigation of the ZrSiO₄-K₂ZrSi₃O₉-K₂ZrSi₆O₁₅ system brought to light new data regarding the geochemical behaviour of zirconium in igneous rocks.     

Mineralogy, geochemistry and uses of the mordenite–bentonite ash-tuff beds of Los Escullos, Almería, Spain

The mordenite ore deposit of Los Escullos has a surface area of 10⁶ m² with an average thickness of 5 m and estimated reserves of 7,500,000 tons of mordenite–bentonite. It is made up of horizontal layers of interbedded epiclastic tuffs with volcanic bentonitised materials which have been subjected to hydromagmatic activity. The layers are essentially composed of bentonite and mordenite with lesser amounts of quartz, cristobalite, biotite, plagioclase, chlorite, amphiboles, titanomagnetite, ilmenite and calcite. The harder layers display a higher proportion of plagioclase crystals and are enriched in Al₂O₃, CaO, Fe₂O₃, TiO₂, P₂O₅, Cu, Zn, Co, Cr, Ni and V, while the more altered layers contain larger contents of SiO₂, K₂O and Y. The amount of sodium increases (from 2% to 4%) relative to depth. Alteration processes resulted in a reduction in the contents of CaO, K₂O and MnO and increase in Na₂O and MgO. The beds of volcanic ash-tuffs have been devitrified by hydrothermal solutions giving rise to bentonites and sodium- and silica-rich residual fluids which have partly crystallized as mordenite and cristobalite. The raw material (mordenite–bentonite) can be improved removing biotite (magnetic separation) and plagioclase and quartz (by floating methods); however, the mordenite–bentonite mineral assemblage is practically impossible to separate due to the size of the crystals (average 0.5 μm under SEM–EDAX). In turn, this upgraded raw material has very useful properties (total area=520 m²/g and cation exchange capacity=70 meq/100 g) which may make it suitable for use in absorption processes (e.g. deodorization, cationic exchange), catalysis and molecular sieving.     

Cervandonite-(Ce) in ores of the Berezitovoe deposit: Second finding in the world

The supposedly second finding of rare arsenosilicate cervandonite-(Ce) in the world is characterized. The mineral was recognized in the ore-bearing metasomatic rocks of the Berezitovoe gold-base metal deposit (Upper Priamurye, Russian Far East) in association with quartz, biotite, muscovite, orthoclase, garnet (almandine-spessartine), tourmaline, basic plagioclase, and sulfides. The cervandonite is represented by optically homogeneous and heterogeneous aggregates with visible crystals from 10 fum to 0.1–0.3 mm in size. Based on the microprobe analysis, the average chemical composition of the homogeneous cervandonite-(Ce) aggregates is as follows (wt %): Ce₂O₃ - 13.00, La₂O₃ - 5.70, Nd₂O₃ - 5.20, Pr₂O₃ - 1.41, Y₂O₃ - 0.77, Sm₂O₃ - 0.77, Eu₂O₃ - 0.23, Gd₂O₃ - 0.54, Dy₂O₃ - 0.31, ThO₂ - 1.12, UO₂ - 0.30, TiO₂ - 12.86, Al₂O₃ - 9.24, Fe₂O₃ - 8.93, FeO - 2.68, CaO - 0.14, SiO₂ - 19.98, As₂O₃ - 16.19. The comparative study of the cervandonite-(Ce) from the Berezitovoe deposit and the analogous minerals from the Alpine mica gneiss of Mt. Pizzo Cervandone (Central Alps) showed that the former mineral can be assigned to a new variety of cervandonite-(Ce) in terms of its compositional features. This variety is characterized by an ordered stoichiometric composition corresponding to the simpler theoretical formula (Ce,Nd,La)(Fe³⁺, Fe²⁺, Ti⁴⁺, Al)₃ (Si₂As³⁺)₃O₁₂.     

Thermodynamics of multicomponent pyroxenes: II. Phase relations in the quadrilateral

The model for the thermodynamic properties of multicomponent pyroxenes (Part I) is calibrated for ortho- and clinopyroxenes in the quadrilateral subsystem defined by the end-member components Mg₂Si₂O₆, CaMgSi₂O₆, CaFeSi₂O₆, and Fe₂Si₂O₆. This calibration accounts for: (1) Fe-Mg partitioning relations between orthopyroxenes and augites, and between pigeonites and augites, (2) miscibility gap features along the constituent binary joins CaMgSi₂O₆-Mg₂Si₂O₆ and CaFeSi₂O₆-Fe₂Si₂O₆, (3) calorimetric data for CaMgSi₂O₆-Mg₂Si₂O₆ pyroxenes, and (4) the P-T-X systematics of both the reaction pigeonite=orthopyroxene+augite, and miscibility gap featurs, over the temperature and pressure ranges 800–1500°C and 0–30 kbar. The calibration is achieved with the simplifying assumption that all regular-solution-type parameters are constants independent of temperature. It is predicated on the assumptions that: (1) the Ca-Mg substitution is more nonideal in Pbca pyroxenes than in C2/c pyroxenes, and (2) entropies of about 3 and 6.5 J/K-mol are associated with the change of Ca from 6- to 8-fold coordination in the M2 site in magnesian and iron C2/c pyroxenes, respectively. The model predicts that Fe²⁺-Mg²⁺ M1-M2 site preferences in C2/c pyroxenes are highly dependent on Ca and Mg contents, with Fe²⁺ more strongly preferring M2 sites both in Ca-rich C2/c pyroxenes with a given Fe/(Fe+Mg) ratio, and in magnesian C2/c pyroxenes with intermediate Ca/(Ca+Fe+Mg) ratios.The proposed model is internally consistent with our previous analyses of the solution properties of spinels, rhombohedral oxides, and Fe-Mg olivines and orthpyroxenes. Results of our calibration extend an existing database to include estimates for the thermodynamic properties of the C2/c and Pbca pyroxene end-members clinoenstatite, clinoferrosilite, hedenbergite, orthodiopside, and orthohedenbergite. Phase relations within the quadrilateral and its constitutent subsystems are calculated for temperatures and pressures over the range 800–1700°C and 0–50 kbar and compare favorably with experimental constraints.     

The crystal chemistry of lithium and Fe3+ in synthetic orthopyroxene

Lithian ferrian enstatite with Li₂O = 1.39 wt% and Fe₂O₃ 7.54 wt% was synthesised in the (MgO–Li₂O–FeO–SiO₂–H₂O) system at P = 0.3 GPa, T = 1,000°C, fO₂ = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å³. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula ^M2(Mg_0.59Fe _0.21 ²⁺ Li_0.20) ^M1(Mg_0.74Fe _0.20 ³⁺ Fe _0.06 ²⁺ ) Si₂O₆. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe³⁺ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe³⁺ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe²⁺) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe³⁺, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe²⁺-Mg ordering process in octahedral sites.     

Molecular orbital calculations of vibrations in three-membered aluminosilicate rings

Ab initio, molecular orbital calculations at the 3–21G^* level were carried out on H₆Si₃O₉, [H₆Si₂AlO₂]^1?, [H₆SiAl₂O₉]^2?, and [H₆A1₃O₉]^3? cyclic molecules in order to determine their structures and vibrational frequencies. These three-membered rings were found to have minima in their potential energy surfaces indicating stability of the species. The H₆Si₃O₉ ring was found to be slightly non-planar, but the [H₆SiAl₂O₉]^2? and [H₆Al₃3O₉]^3? configurations are more planar. Vibrational frequencies of the Raman-active, bridging oxygen “breathing” modes increase with Si⁴⁺ content. Galeener's (1982a, b) assignment of the D₂ peak (606 cm^?1) in the Raman spectrum of vitreous silica to an oxygen breathing mode in rings of three SiO₄ tetrahedra is reconfirmed. Correlation of the ring breathing mode frequencies as a function of (AI/AI + Si) with Raman peaks in the SiO₂-NaAlSiO₄ system is high. Three-membered aluminosilicate rings are likely to exist and give rise to Raman peaks between 540 and 600 cm_?1 in fully-polymerized aluminosilicate glasses.     

Boron substitution in diopside evaluated through 11B nuclear reaction analysis

 Nuclear reaction analyses on boron in flux-grown Me³⁺- and Na⁺-doped diopside crystals utilising the ¹¹B(p,2α)⁴He reaction in conjunction with EMP analyses for major elements and optical absorption spectroscopy for determination of Me-valence state distributions show that appreciable amounts of B may enter the diopside lattice in crystals produced in Na₂B₄O₇ fluxes. The results indicate that the substitution ^[6]Me^3+[4]B^3+[6]Mg²⁺ ₋₁ ^[4]Si⁴⁺ ₋₁ operates in the present diopside samples in addition to the coupled substitution ^[6]Me^3+[8]Na^+[6]Mg²⁺ ₋₁ ^[8]Ca²⁺ ₋₁. The specific NRA technique applied allows for quantitative, high resolution (ca. 5 μm) B analyses at ppm level as well as high-resolution and high-contrast imaging of B-concentration patterns in minerals. The estimated detection limit and relative error of the B analyses are 10 ppm and 5–10%, respectively. Received: 20 September 1999 / Accepted: 6 June 2000     

Characterization of leached layers on olivine and pyroxenes using high-resolution XPS and density functional calculations

High-resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of olivine [(Mg_0.87Fe_0.13)₂SiO₄], bronzite [(Mg_0.8Fe_0.2)₂Si₂O₆] and diopside [Ca(Mg_0.8Fe_0.2)Si₂O₆] were collected before and after leaching in pH ∼2 solutions with the Kratos magnetic confinement charge compensation system which minimizes differential charge broadening. The leached samples yield Si 2p, Mg 2p, Ca 2p and O 1s XPS spectral linewidths and lineshapes similar to those collected from the respective pristine samples prior to leaching. As with previous XPS studies on crushed samples, our broadscan XPS spectra show evidence for initial, preferential leaching of cations (i.e., Ca²⁺ and Mg²⁺) from the near-surface of these minerals. The O 1s spectra of leached olivine and pyroxenes show an additional peak due to OH⁻, which arises from H⁺ exchange with near-surface cations (Ca²⁺ and Mg²⁺) via electrophilic attack of H⁺ on the M-O-Si moiety to produce the H₂Mg(M1)SiO_4(surf) complex at olivine surfaces, and two complexes, H₂Mg(M1)Si₂O_6(surf) and H₄Si₂O_6(surf) at diopside and enstatite surfaces. The olivine and pyroxene surface complexes H₂Mg(M1)SiO_4(surf) and H₂Mg(M1)Si₂O_6(surf) have been proposed previously, but the second pyroxene surface complex H₄Si₂O_6(surf) has not. Two electrophilic reactions occur in both olivine and pyroxene. For olivine, the more rapid attacks the M2-O-Si moiety producing H₂Mg(M1)SiO_4(surf); while the second attacks the M1-O-Si moiety ultimately producing H₄SiO₄ which is released to solution. For pyroxenes, the first electrophilic reaction produces H₂Mg(M1)Si₂O_6(surf), while the second produces.H₄Si₂O_6(surf). These two reactions are followed by a nucleophilic attack of H₂O (or H₃O⁺) on Si of H₄Si₂O_6(surf). This reaction is responsible for rupture of the brigding oxygen bond of the Si-O-Si moiety and release of H₄SiO₄ to solution. The intensity of the OH⁻ peak for the leached pyroxenes is about double the OH⁻ intensity for the leached olivine, consistent with the equivalent of about a monolayer of the above surface complexes being formed in all three minerals.Valence band XPS spectra and density functional calculations demonstrate the remarkable insensitivity of the valence band to leaching of Ca²⁺ and Mg²⁺ from the surface layers. This insensitivity is due to a dearth of Ca and Mg valence electron density in the valence band: the Ca-O and Mg-O bonds are highly ionic, with metal-derived s orbital electrons taking on strong O 2p character. The valence band spectrum of leached olivine shows an additional very weak peak at about 13.5 eV, which is assigned to Si 3s valence orbitals in the surface complex H₂Mg(M1)SiO₄, as indicated by high quality density functional calculations on an olivine where Mg²⁺ in M2 is replaced by 2H⁺. The intensity of this new peak is consistent with formation of the equivalent of a monolayer of the surface complex.     

Quantification of water content and speciation in natural silicic glasses (phonolite, dacite, rhyolite) by confocal microRaman spectrometry

The determination of total water content (H₂O_T: 0.1-10 wt%) and water speciation (H₂O_molecular/OH) in volcanic products by confocal microRaman spectrometry are discussed for alkaline (phonolite) and calcalkaline (dacite and rhyolite) silicic glasses. Shape and spectral distribution of the total water band (H₂O_T) at ∼3550 cm⁻¹ show systematic evolution with glass H₂O_T, water speciation and NBO/T. In the studied set of silicic samples, calibrations based on internal normalization of the H₂O_T band to a band related to vibration of aluminosilicate network (TOT) at ∼490 cm⁻¹ vary with glass peraluminosity. An external calibration procedure using well-characterized glass standards is less composition-dependent and provides excellent linear correlation between total dissolved water content and height or area of the H₂O_T Raman band. Accuracy of deconvolution procedure of the H₂O_T band to quantify water speciation in water-rich and depolymerized glasses depends on the strength of OH hydrogen bonding. System confocal performance, scattering from embedding medium and glass microcrystallinity have a crucial influence on accuracy of Raman analyses of water content in glass-bearing rocks and melt inclusions in crystals.     

Ionic conductivity in sodium magnesium silicates

Na₂MgSiO₄ crystals prepared hydrothermally at 700° C and 3,000 atm are related to carnegieite with SG Pmn2₁, a=7.015(2), b=10.968(2), and c=5.260(1). Na conductivity in Na₂MgSiO₄ is 3.0×10^?5 (ohm-cm)^?1 at 300° C but can be raised to 1.1×10^?3 (ohm-cm)^?1 by creating Na vacancies in the composition Na_1.9Mg_0.9Al_0.1O₄. Na₄Mg₂Si₃O₁₀ is also a cristobalite-related carnegieite with the orthorhombic cell a=10.584(7), b=14.328(7), and c=5.233(5). The Na conductivity of Na₄Mg₂Si₃O₁₀ is 4.8×10^?3 (ohm-cm)^?1 at 300° C.     

Phlogopites and potassic richterites from mica nodules in South African kimberlites

Mica nodules from the Dutoitspan and Wesselton mines, Kimberley can be divided into two groups: diopside-phlogopite nodules and potassic richterite-phlogopite nodules. The latter is characterized by the presence of abundant potassic richterite (less than 50% by volume) and large size of the crystals (up to 1 cm in length). It seems this type nodule is the first finding. Phlogopites and potassic richterites show a rather wide variations of major elements they have low Al₂O₃ and high Fe₂O₃, with Fe⁺³ in addition to Al⁺³ in the tetrahedral sites. It is believed that the mica nodules would be produced from kimberlitic and related magmas under moderate temperature and pressure conditions.     

Florencite-(Sm)—(Sm,Nd)Al3(PO4)2(OH)6: A new mineral species of the alunite-jarosite group from the subpolar urals

Florencite-(Sm), a new mineral species of the florencite subgroup, was found in association with xenotime-(Y) in quartz veins of the Maldynyrd Range of the Subpolar Urals as thin zones within rhombohedral crystals of florencite-(Ce) with faceting by { 01[`1]1}\{ 01\bar 11\} and { 10[`1]2}\{ 10\bar 12\} . The thickness of particular florencite-(Sm) zones is 0.01–0.1 mm, and the total thickness of a series of such zones is 1–3 mm. Florencite-(Sm) is colorless and pale pink or pale yellow with white streaks; its Mohs hardness is 5.5–6.0. Its measured and calculated densities are 3.70 and 3.743 g/cm³, respectively. The mineral is transparent, nonpleochroic, and uniaxial (positive), and ω = 1.704(2) and ɛ = 1.713(2). The electron beam’s fluorescence spectrum was 592 nm (intense green luminescence of Sm³⁺) and 558 nm (yellow luminescence of Nd³⁺). The chemical composition was as follows (microprobe, average of 2 WDS, wt %): 0.62 La₂O₃, 3.29 Ce₂O₃, 1.05 Pr₂O₃, 10.31 Nd₂O₃, 12.62 Sm₂O₃, 0.41 Eu₂O₃, 2.30 Gd₂O₃, 0.13 Dy₂O₃, 0.71 SrO, 0.35 CaO, 29.89 Al₂O₃, 26.14 P₂O₅, 0.85 SO₃, 0.09 SiO₂, 88.76 in total; 10.74 H₂O (meas.). The empirical formula based on 14 oxygen atoms is (Sm_0.38Nd_0.32Gd_0.07Ce_0.10Pr_0.03La_0.02Eu_0.01Sr_0.04Ca_0.03)1.0Al_3.04(P_1.91S_0.05Si_0.01)_1.97O₁₄H_5.92. The idealized formula is (Sm,Nd)Al₃(PO₄)₂(OH)₆. Mineral is trigonal, space group R3m, a = 6.972(4), c = 16.182(7) ?, V = 681.2 ?³, Z = 3. The XRD pattern is as follows: dln (I) (hkl): 2.925 (10) (113), 1.881 (6) (303), 2.161 (5) (107), 5.65 (4) (101), and 3.479 (4) (110). The IR spectrum: 466, 510, 621, 1036, 1105, 1223, 2957, and 3374 cm⁻¹.