Showing papers in "European Journal of Mineralogy in 2015"

Low-temperature chlorite geothermometry: a graphical representation based on a T–R2+–Si diagram

Abstract: The chlorites are good indicators of rock history because their wide compositional variations are sensitive to the formation conditions, like pressure ( P ), temperature ( T ), redox state, fluid composition. Accordingly, many geothermometers based on their composition, either empirically or thermodynamically, have been proposed during the last 30 years, especially in low-temperature contexts ( T < 350°C). This paper presents a graphical tool that considerably facilitates the use of two of the most recent chlorite thermometers for low- and very-low- T chlorites. The temperature–composition relationships for low- T chlorites are represented in T –Si– R2+ diagrams, allowing chlorite compositions to be predicted as a function of temperature or, conversely, temperature to be estimated from compositional fields of natural chlorites. This graphical projection is based on a comparison of the parameters (ideal chlorite compositions and calculated T ) predicted by geothermometers with analyses of natural chlorites for which independent T estimates are available over a range of geological environments. The new T –Si– R2+ diagram provides a practical tool for thermometric purposes in the applicability range of the considered models, in particular for diagenesis and low-grade metamorphism.

Lime mortar consolidation with nanostructured calcium hydroxide dispersions: the efficacy of different consolidating products for heritage conservation

Abstract: This paper analyses the efficacy of dispersions of nanoparticles of calcium hydroxide for consolidating lime mortars, according to three variables: the type of dispersion (three consolidating compounds—CaLoSil ® , Nanorestore ® and Merck ® —with different-sized calcium hydroxide particles); the concentration of the dispersion (5 and 25 g/L of Ca(OH) 2 in isopropyl alcohol); and the state of the sample (comparison of saturated and non-saturated samples). The outcome of the consolidation process was studied in terms of improved carbonation of the mortar, mineralogy (by means of X-ray diffraction and thermogravimetric analyses), texture (study of the porosity by mercury intrusion porosimetry) and compactness (measurement of ultrasonic velocity propagation through samples). To ensure that the treatment had no negative effects on the physical characteristics of the mortars, we performed microstructural (phase morphology studied by means of scanning electron microscopy) and aesthetic (colour and lightness measured by spectrophotometry) analyses. Of the different dispersions, CaLoSil ® at 5 g/L produced the most significant improvement in the degree of carbonation and in the compactness of the mortar, thanks to the precipitation of small crystals of calcite and aragonite in the pores located between the matrix and the aggregate grains. This product also caused the least significant chromatic changes (slight decrease in lightness and yellowing) and the greatest increase in ultrasonic propagation velocity through the mortar samples. This research has specific application in restoration work that involves consolidation of lime mortars, especially in tropical climates or in confined environments with high humidity levels (such as deep hypogea).

Transformation of amorphous calcium carbonate into monohydrocalcite in aqueous solution: a biomimetic mineralization study

Abstract: Monohydrocalcite (MHC, CaCO 3 · H 2 O) is a thermodynamically metastable phase relative to calcite and aragonite in aqueous solution. Although MHC occurs broadly in organisms, little information about its biogenic origin is available. In this paper, a series of amorphous calcium carbonates (ACCs) with different Mg 2+ contents were first synthesized in the presence of polyaspartic acid (PASP), and the phase transformations of the PASP-regulated Mg-ACCs (PASP-Mg-ACCs) were then studied under different medium conditions. The structure, morphology and composition of the precursor PASP-Mg-ACCs and transformation products were investigated by using a wide range of techniques, including XRD, FT-IR, FESEM, TG-DTA, 13 C NMR and ICP-AES. Our results show that PASP-Mg-ACC with 24.71 mol% Mg 2+ can be transformed into MHC, without formation of hydromagnesite or other hydrated magnesium carbonates, whereas the PASP-Mg-ACCs with 2+ resulted in magnesian calcite and aragonite. Time-course transition experiments unveiled that the transformation from PASP-Mg-ACCs to crystalline phases proceeds through the dissolution of the initial precursor PASP-Mg-ACCs and the subsequent crystallization of the secondary mineral phases. The formation of different secondary minerals depends not only on the Mg 2+ but also on the PASP content in precursor PASP-Mg-ACCs. Because of the exclusive formation of MHC from PASP-Mg-ACC under current biomimetic conditions, biomacromolecule-regulated Mg-ACC may act as the transient precursor and be responsible for the biogenesis of MHC. The current results contribute to the elucidation of the biogenic origin and role of MHC in nature.

Na-Ca carbonates synthesized under upper-mantle conditions: Raman spectroscopic and X-ray diffraction studies

Abstract: The new Na4Ca(CO3)3, Na2Ca3(CO3)4 and Na2Ca4(CO3)5 compounds were synthesized in the system Na2CO3–CaCO3 in multianvil experiments at 6 GPa and characterized by Raman spectroscopy. In addition, the Na2Ca3(CO3)4 compound was studied using in situ energy dispersive and single-crystal X-ray diffraction. Single bands in the CO32− symmetric stretching region ( v1 ) and out-of-plane bending region ( v2 ) in the Na4Ca(CO3)3 Raman spectrum suggest a single crystallographically distinct carbonate group in the structure. In contrast, the spectra of Na2Ca3(CO3)4 and Na2Ca4(CO3)5 show two and three bands, respectively, in both the symmetric stretching region ( v1 ) and out-of-plane bending region ( v2 ), suggesting more than one crystallographically distinct carbonate group in the unit cell. Raman activity in the forbidden v2 mode and multiple bands are observed in the in-plane bending region ( v4 ) for the three compounds, proving the reduction of site symmetry of the CO32− ions with the loss of the threefold rotation axis ( D 3h → D 2h or C s). Such a decrease in symmetry suggests distortion of the group itself, but may be attained by rearrangements of the coordinated metal cations as in the aragonite-group carbonates. At 6.5 GPa and 1000°C, the structure of Na2Ca3(CO3)4 was found to be orthorhombic or monoclinic with a β angle close to 90° and the lattice parameters: a = 7.3357(6) A, b = 8.0377(9) A, and c = 31.5322 (32) A, with V = 929.59(14) A3. No structural changes were observed during pressure decrease down to 1 GPa, while a discontinuous increase in unit-cell parameters and volume was observed upon decompression from 1 GPa at room temperature. This indicates a pressure-induced phase transition to a structurally related ambient-pressure phase. The abnormally long c -parameter and proximity of the β-angle to 90° of Na2Ca3(CO3)4 at ambient conditions suggest that, in the monoclinic system, the metric symmetry is higher than the Laue symmetry, which is a common sign for merohedral twinning.

Mayenite supergroup, part I: Recommended nomenclature

Abstract: The mayenite supergroup, accepted by the IMA-CNMNC (proposal 13-C), is a new mineral supergroup comprising two groups of minerals isostructural with mayenite (space group No. 220, I43d, a ! 12 A˚) with the general formula X12T14O32" x(OH)3x(W6" 3x): the mayenite group (oxides) and the wadalite group (silicates), for which the anionic charge over 6 W sites is " 2 and " 6, respectively. Currently only minerals dominated by end-members with x ¼ 0 and the simplified formula X12T14O32(W6) have been reported. The mayenite group includes four minerals: (1) chlormayenite, Ca12Al14O32(&4Cl2); (2) chlorkyuygenite, Ca12Al14O32((H2O)4Cl2); (3) fluormayenite, Ca12Al14O32(&4F2); and (4) fluorkyuygenite, Ca12Al14O32((H2O)4 F2). The wadalite group comprises the two mineral species wadalite, with the end-member formula Ca12Al10Si4O32(Cl6), and eltyubyuite, with the end-member formula Ca12Fe 3þ 10Si4O32(Cl6). Current research on minerals and synthetic compounds indicates that minerals close to the composition of ideal end-members, such as Ca12Fe 3þ 10Si4O32(F6), Ca12Si9Mg5O32(Cl6) and Ca12Al14O30(OH)6(&6), could be found in Nature. A detailed re-examination of the type specimens of mayenite, originally described as Ca12Al14O33, indicates that Ca12Al14O32(&4Cl2) is its correct end-member formula. Consequently, we are redefining and renaming mayenite as chlormayenite, Ca12Al14O32(&4Cl2), whereas the name mayenite would be reserved for a potential mineral with the end-member composition Ca12Al14O32(&5O). As a consequence, the mineral brearleyite, Ca12Al14O32(&4Cl2), described in 2011 is identical with chlormaye- nite and is therefore discredited. By analogy with chlormayenite we changed the name of kyuygenite into chlorkyuygenite.

Petrophysical properties of a granite-protomylonite-ultramylonite sequence: insight from the Monte Grighini shear zone, central Sardinia, Italy

Abstract: The Monte Grighini intrusive complex (central-west Sardinia) has been affected by a 1.5 km wide late-Variscan shear zone; microstructures and deformation fabrics indicate that high strain domains resulted in sharp transitions among protomylonite to ultramylonite. A representative geological cross section of the shear zone has been sampled, as well as samples from outside the mylonitic belt for use as slightly deformed protolith reference samples. Physical and mechanical analyses were performed on each group in order to evaluate a possible correlation between petrophysical properties (density, porosity and mechanical strength) and the degree of mylonitic deformation. Ultramylonites are generally characterized by a higher solid-phase density (2.82–2.85 g/cm3) than less deformed protomylonites and mylonites (2.73–2.79 g/cm3), testifying to the formation of high-density minerals with an increase in deformation. Conversely, bulk density tends to decrease as deformation increases (from 2.52–2.57 g/cm3 to 2.47–2.48 g/cm3) due to the total porosity increase occurring during mylonitization. The mean values of total porosity range from 6.33 to 9.27 % in protomylonites and mylonites and from 12.01 to 12.85 % in ultramylonites. The relatively high value of porosity in more deformed ultramylonites is the result of the sum of closed micropores and open pores produced by different processes. Mechanical strength measurements show a noticeable anisotropy, with higher strength values measured applying the load perpendicular to foliation (Z axis) and lower values obtained parallel to it (X,Y axes). In the Monte Grighini mylonite the anisotropy is due to the distribution of pores and to the preferred orientation of new minerals, as highlighted by the correlation between scalar physical properties (solid, real and bulk densities, porosity) and vector properties (resistance to punching or uniaxial compressive strengths). The results show that the degree of deformation of mylonitic rocks can be characterized by petrophysical properties, in order to shed light on the tectonic processes experienced at depth.

Mayenite supergroup, part III: Fluormayenite, Ca 12 Al 14 O 32 [□ 4 F 2 ], and fluorkyuygenite, Ca 12 Al 14 O 32 [(H 2 O) 4 F 2 ], two new minerals from pyrometamorphic rocks of the Hatrurim Complex, South Levant

Abstract: Two new mineral species of the mayenite group, fluormayenite Ca12Al14O32[□4F2] ( I ![Formula][1] 3 d , a = 11.9894(2) A, V = 1723.42(5) A3, Z = 2) and fluorkyuygenite Ca12Al14O32[(H2O)4F2] ( I ![Formula][2] 3 d , a = 11.966(2) A, V = 1713.4(1) A3, Z = 2), are major constituents of larnite pyrometamorphic rocks of the Hatrurim Complex (Mottled Zone) distributed along the Dead Sea rift on the territory of Israel, Palestinian Autonomy and Jordan. Holotype specimens of fluormayenite and fluorkyuygenite were collected at the Jabel Harmun, Judean Mts., Palestinian Autonomy and in the Hatrurim Basin, Negev Desert, Israel, respectively. Mineral associations of holotype fluormayenite and fluorkyuygenite are similar and include larnite, shulamitite, Cr-containing spinel–magnesioferrite series, ye’elimite, fluorapatite–fluorellestadite, periclase, brownmillerite, oldhamite as well as the retrograde phases portlandite, hematite, hillebrandite, afwillite, foshagite, ettringite, katoite and hydrocalumite. Fluormayenite and fluorkyuygenite crystals, usually < 20 μm in size, are colourless, in places with greenish or yellowish tint, the streak is white. Both minerals are transparent with a vitreous lustre; they do not show fluorescence. Fluormayenite and fluorkyuygenite are isotropic and have similar refractive indices: n = 1.612(3) and n = 1.610(3) (589 nm), respectively. The hardness of fluormayenite and fluorkyuygenite is H (Mohs) 5½–6; VHN load 50 g, 771(38) kg mm−2; and 5–5½; VHN load 50 g, 712(83) kg m−2, respectively. Both minerals have the microporous tetrahedral framework structure characteristic of the mayenite supergroup. In fluormayenite 1/3 of the structural cages are occupied by fluorine. In fluorkyuygenite, in addition to fluorine and negligible amounts of OH, H2O molecules occupy about 2/3 of the cages. The holotype fluormayenite from Jabel Harmun has the crystal chemical formula (Ca11.951Na0.037)Σ11.987(Al13.675Fe3+0.270Mg0.040Si0.009P0.005S6+0.013)Σ14.013 O31.503(OH)1.492[□4.581F1.375Cl0.044]Σ6, fluorkyuygenite from the Hatrurim Basin has the composition Ca12.034(Al13.344Fe3+0.398 Si0.224)Σ13.966O32[(H2O)3.810F1.894 (OH)0.296]Σ6. Raman spectra of fluormayenite and fluorkyuygenite in the spectral region 200–1000 cm−1 are similar and are characterized by the four strong main bands at about 320 (ν2 AlO4), 520 (ν4 AlO4), 700, 770 (ν1 AlO4) cm−1. In the O-H vibration region fluorkyuygenite shows a broad band between 2600–3500 cm−1 (νH2O). The molecular water is completely released from the fluorkyuygenite structure at about 400°C. Fluorkyuygenite crystallized initially as fluormayenite, which later was altered under influence of water vapour-enriched gases during a combustion process. Fluormayenite has been synthesized and fluorkyuygenite is an analogue of the recently discovered chlorkyuygenite, Ca12Al14O32[(H2O)4Cl2], from the Northern Caucasus, Russia. [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif

Mineralogy of the Koktokay No. 3 pegmatite, Altai, NW China: implications for evolution and melt–fluid processes of rare-metal pegmatites

Abstract: The Koktokay No. 3 pegmatite is the largest Li-Be-Nb-Ta-Cs pegmatitic rare-metal deposit of the Chinese Altai orogenic belt, and is famous for its concentric ring zonation pattern (nine internal zones) and rare-metal reserves. In this paper, we present the results of major and trace element analysis for garnet, tourmaline, and beryl from the outer to inner zones of the No. 3 pegmatite. From previous studies on tourmaline and beryl, potential tracers of the degree of pegmatite evolution could be found by comparing with accepted indicators and evolutionary trends from the outer to inner zones of this pegmatite. The Sc, Y, Li, Ta contents and Y/Ho value of garnet, together with the Ti, Ca, Na, Pb, Bi and REE contents of tourmaline, and the Fe, Ga and Rb concentrations of beryl could be possible tracers of the degree of evolution of pegmatites. The textures and internal structures (homogeneity, oscillatory pattern, heterogeneous rims, replacement structures) of minerals in the pegmatite suggest that the rock underwent (1) rapid undercooling and crystallization after emplacement, resulting in the formation of an unidirectional solidification texture (UST), and then (2) became relatively stable, forming coarse crystals in outer zones, and finally (3) experienced disequilibrium crystallization, leading to the formation of complex internal structures of minerals in the inner zones, mainly caused by exsolution of more fluid and the formation of immiscible melts with different alkali contents. The evolutionary trend and the internal structures of tourmaline and beryl indicate that the formation of the Koktokay No. 3 pegmatite was controlled mainly by fractional crystallization. The convex tetrad effect, non-CHARAC Y/Ho values, and extreme Eu depletion of garnet suggest that immiscibility, which is a significant mechanism during the formation of the No. 3 pegmatite, occurred during emplacement. The differences in composition and internal structures of the minerals between the outer and inner zones of the No. 3 pegmatite suggest that there was an abrupt change, during transition from the melt stage to the melt–fluid stage, resulting from a decompression event, which led to the exsolution of the fluid and initiated the Li-Ta-Cs deposition in the pegmatite.

Ordering of water in opals with different microstructures

Abstract: Opal has long fascinated scientists. It is one of the few minerals with an amorphous structure, and yet, compared to silica glass, it is highly organized on the mesoscale. By means of inelastic neutron scattering (INS), we could document that in four samples of opal at low temperature an ice-like structure of water is present, with details depending on microstructural characteristics. While FTIR spectra for all samples are nearly identical and thus not very informative, INS shows clear differences, highlighting the significance of microstructures. Neutron diffraction at 100 K on one of the opal samples provides evidence for crystalline cubic ice.

The crystal structure of flamite and its relation to Ca2SiO4 polymorphs and nagelschmidtite

Abstract: The recently accepted new mineral flamite IMA No. 2013–122, (Ca,Na,K) 2 (Si,P)O 4 , found in the pyrometamorphic rocks of the Hatrurim Formation, Israel, was reported to crystallize in the hexagonal space group P 6 3 with unit-cell parameters a = 43.3726(18), c = 6.8270(4) A. A careful re-examination of single crystals from the type locality and holotype material, however, shows that flamite is better described by the formula Ca 8−x (Na,K) x (SiO 4 ) 4−x (PO 4 ) x and that it crystallizes in the space group Pnm 2 1 , a = 9.3845(6), b = 21.7310(14), c = 6.8346(4) A, V = 1393.81(15) A3, Z =4 and is isostructural with the known synthetic P-doped clinker phase Ca 15 □(SiO 4 ) 6 (PO 4 ) 2 . The structure is a derivative of the hexagonal high-temperature variety of dicalcium-silicate, α-C 2 S, and is characterized by a cyclic triplet of individuals rotated 120° around c , interpreted as symplectite-like transformation “twinning” derived from α-C 2 S. The composition of intergrown flamite lamellae is chemically variable concerning the degree of Na, K and P substitution. We present the structure of flamite and discuss its close relationship to nagelschmidtite, Ca 7 (SiO 4 ) 2 (PO 4 ) 2 , and the high-temperature polymorphs of C 2 S.

Magnetite from the Cogne serpentinites (Piemonte ophiolite nappe, Italy). Insights into seafloor fluid–rock interaction

Abstract: In the Cogne area (Aosta Valley, Western Italian Alps), magnetite mineralization occurs associated with different types of serpentinite (pseudomorphic, rodingitic and magnetite-rich serpentinites), which are also heterogeneous in terms of bulk chemical composition, mineral assemblage and mineral chemistry. The mineralization is hosted by a lizardite-, ±chrysotile-bearing serpentinite showing a pseudomorphic texture after oceanic peridotite. It contains fine-grained magnetite showing oscillatory zoning with Cr-poor cores (~0.4 wt.% Cr2O3), which are surrounded by Cr-rich inner euhedral rims (up to 17.0 wt.% Cr2O3), mantled in turn by partially resorbed Cr-bearing outer rims (~2.0 wt.% Cr2O3). This dramatic variation of Cr content in magnetite is described by the exchange vector Fe3+ Fe2+ Cr3+−1 (Mn, Zn, Ni) 2+−1. The absence of Cr-rich spinel cores suggests that the source of chromium was the Cr-Tschermak component of the orthopyroxene, made available during the serpentinization-related breakdown. In these rocks, lizardite, the primary serpentine phase, is partially overgrown by prograde antigorite, indicating that serpentinization occurred under relatively low- T conditions in a preorogenic ( i.e. , oceanic) setting, and was followed by an Alpine metamorphic re-equilibration. Rodingitic serpentinite and serpentinite rich in magnetite are composed of, in highly variable amounts, diopside (locally with inclusions of partially disordered graphite), calcite, magnetite, andradite/hydroandradite, prograde olivine, brucite and serpentine (mostly antigorite but also relict lizardite), with minor chlorite and accessory apatite. Magnetite content can be very high. In these rocks, magnetite is exceptionally Cr-poor (almost Cr-free). Such almost Cr-free magnetite is characterized by significant Fe2+ ↔ Mg substitution (2–15 mol.% MgFe2O4). Crystal-chemical investigations confirm that Mg, as in magnesioferrite, shows a strong preference for the octahedral site. Due to Fe2+ ↔ Mg substitution, the Fe2+ content available for Fe2+ – Fe3+ electron hopping in the octahedral site decreases leaving Fe3+ in excess and giving rise to a charge increase. Additionally, a small Fe3+ - Fe2+ disorder is present at the tetrahedral site (Fe2+T =0.07 apfu). The bulk-rock compositions and the mineral associations of rodingitic serpentinite and serpentinite rich in magnetite point to a strong metasomatism and iron mobilization sustained by CO2-bearing fluids, developed at the expense of the host serpentinite. These processes likely occurred on the Tethyian seafloor, mediated by fluids sourcing from hydrothermal vents. Thermodynamic modelling suggests that mineral assemblages observed in the Cogne area are consistent with a process of serpentinization coupled with Ca (±Al) metasomatism at 300–360°C. This might have been driven by carbon-saturated C-O-H fluids characterized by CO2 contents comparable to present-day seawater, capable of fixing the redox potential of rocks close to the fayalite–magnetite–quartz buffer. Nevertheless, magnetite and associated Fe-Ni sulphides suggest slight variations in f O2 (and f S2) conditions recorded, ranging from relatively reducing (magnetite–heazlewoodite–pentlandite ±pyrrhotite) towards rather oxidizing (magnetite–millerite–pyrite) assemblages.

Geochemistry and zircon U-Pb geochronology of magmatic enclaves in trachytes from the Euganean Hills (NE Italy): further constraints on Oligocene magmatism in the eastern Southern Alps

Abstract: This study presents the results of the geochemical and geochronological investigation of magmatic enclaves in trachytes from the Euganean Hills (NE Italy). The Euganean Hills magmatic district is the most recent (Eocene-Oligocene) volcanic distric within the Veneto Volcanic Province (VVP), which represents the main magmatic event in the eastern Southern Alps. The studied enclaves include intrusive and crystal mush types, the latter characterised by embayments of the host trachyte towards the core of the enclaves. Both types have zircon U-Pb ages of ~30–32 Ma, indicating that they are contemporaneous with the second Euganean magmatic phase. Amphibole-bearing intrusive enclaves (syenites and quartzo-monzonites) and crystal mushes have similar major and trace element compositions ( e.g. REE, Rb, Ba, K, Nb, Pb, Th and Y contents) as those of the host trachyte. They are interpreted as magma chamber solidification fronts with different degrees of crystallization, which were caught as enclaves by the trachytic magma during its ascent. Amphibole-free intrusive enclaves show peculiar trace element compositions (depletion in Th, U, Nb, Ta, MREE and HREE, and marked Eu positive anomaly), in contrast to the compositions of Euganean lavas and other studied enclaves, and are interpreted as cumulative rocks resulting from concentration of crystals fractionated during trachyte–rhyolite evolution. This study confirms that low-pressure fractional crystallisation played a primary role in the evolution of magma in the VVP. The first zircon U-Pb ages from the Euganean rocks prove a Lower Oligocene age for the second Euganean magmatic phase. The use of this robust chronometer should be extended to the Euganean lavas, to better constrain the chronological sequence of eruptive events.

Tin concentration in hydrothermal sulphides related to ultramafic rocks along the Mid-Atlantic Ridge: a mineralogical study

Abstract: Hydrothermal polymetallic sulphides collected along the Mid-Atlantic Ridge and hosted in ultramafic rocks (Ashadze, Logatchev and Rainbow ore fields) are enriched in Sn compared to sulphides associated with volcanic rocks. At Logatchev, the averaged Sn ore concentration reaches 2000 ppm. The distribution of Sn among sulphides was studied using scanning electron microscopy and electron-microprobe analysis. The Sn concentration can reach up to 6 wt.% in sphalerite and 2 wt.% in chalcopyrite. Raman micro-spectroscopy investigation suggests that most of Sn is carried by stannite micro-inclusions in sulphides. According to the mineralogical and chemical studies, the following paragenetic sequence is proposed: (1) Sn (<1 wt.%) first precipitates as solid solution in low-temperature sphalerite; (2) at high temperature (300 °C) and low pH (~3) sphalerite is replaced by chalcopyrite; Sn, previously contained in the low-temperature sphalerite, contributes to the formation of stannite, as micro-inclusions in the replacement front; (3) eventually Sn is distributed within newly formed chalcopyrite (<1 wt.%). Tin enrichment of Zn-Cu ores appears as an indicator of hydrothermal reworking of ultramafic sulphide deposits.

Composition and colouring agents of historical Islamic glazes measured with EPMA and μ-XRD2

Abstract: Glazes from tiles of representative historic Islamic buildings and tableware ceramic from Central Asia, the Middle East, Asia Minor and North Africa were analysed by electron probe microanalysis (EPMA) and two-dimensional micro-X-ray powder diffraction (μ-XRD 2 ). From major element compositions, three main glaze types were identified: alkali, alkali–lead and lead glazes. Quartz frit and clay ceramics form the substrates of the glazes. A slight influence of the ceramic on the glaze compositions can be found for SiO 2 , Al 2 O 3 and K 2 O, but only for quartz frit substrates. PbO and/or alkali oxides were used as fluxes. Na 2 O is the dominant oxide in the alkali flux. MgO and P 2 O 5 are the decisive components for the discrimination between mineral soda and plant ash as a source of the alkali flux. The use of plant ash beside the established mineral soda as flux for the glazes was introduced during the 13 th century in Iran, latest during the 13 th /14 th century in Afghanistan, and during the 14 th /15 th century in Uzbekistan. Hence, a change of the flux happened later for the glazes than for local glass of the same regions. Lead-glaze compositions occur in almost all considered epochs and locations. Colouring ions are Co 2+ (blue), Cu 2+ (green in a Pb-rich matrix), Fe 3+ and Mn 4+ (brown/black) and Mn 3+ (violet). Pigments, such as SnO 2 , SiO 2 and PbSiO 4 , are whitening agents; Pb 2 Sn 2 O 6 was used for yellow colours. Iron-containing clinopyroxenes and Cu-Cr-Mn-oxides are found in black glazes.

Two generations of zoned crystals of columbite-group minerals from granitic aplite–pegmatite in the Gouveia area, central Portugal

Abstract: This research was financially supported by the projects POCTI/35602/CTA/99 and GOLD-Granites, Orogenesis, Long-term strain/stress and Deposition of ore metals - PTDC/Geo-Geo/2446/2012; FCOMP-01-O124-FEDER-029192 through FCT-Portuguese Foundation for Science and Technology.

Crystal chemistry of cation-exchanged forms of epistolite-group minerals, Part I. Ag- and Cu-exchanged lomonosovite and Ag-exchanged murmanite

Abstract: The paper presents the first data on the crystal chemistry of the cation-exchanged forms of layered titanosilicates belonging to the epistolite group. It was found that these heterophyllosilicates have high exchange capacity and selectivity for cations of chalcophile elements (Ag, Cu and Zn) and could be considered as potentially novel raw materials or, more likely, as possible prototypes of cation-selective synthetic microporous materials. The crystal structures of Ag- and Cu-exchanged forms of lomonosovite and Ag-exchanged form of murmanite were studied by single-crystal X-ray diffraction. The topology of the main structural unit, the HOH block, remains unchanged in cation-exchanged forms as compared to the initial lomonosovite Na 4 Ti 4 (Si2O 7 ) 2 O 4 • 2Na 3 PO 4 ( P -1) and murmanite Na 4 Ti 4 (Si 2 O 7 ) 2 O 4 • 4H 2 O ( P -1). In Ag-exchanged murmanite, Ag cations occupy two crystallographically non-equivalent positions: one in the heteropolyhedral ( H ) sheet and another one in the octahedral ( O ) sheet corresponding to the positions of Na in initial murmanite. The crystal structure of the Ag-exchanged form of lomonosovite is characterized by an increased unit-cell parameter c and doubled parameter b as compared to initial lomonosovite. Ten large-cation sites statistically occupied by Ag and Na correspond to the Na sites in the initial lomonosovite: six in the interlayer space, two in the H sheet and two in the O sheet. Silver significantly replaces Na in sites in the interlayer space and in the O sheet, whereas sites in the H sheet are less affected by the ion exchange. Unit-cell parameter c of the Cu-exchanged form of lomonosovite decreases by 3.58% as compared to the initial lomonosovite whereas a and b remain almost the same. The Cu cations occupy two crystallographically independent positions. The Cu(1) site, corresponding to the Na(3) site in the initial lomonosovite, is located in the interlayer space. The low-occupancy Cu(2) site is located on the inversion centre in the O sheet; this site is vacant in the initial lomonosovite. The Cu(2) site is surrounded by six O atoms forming an octahedron distorted due to the Jahn-Teller effect.

Fluid inclusions in ruby from Asian marble deposits: genetic implications

Abstract: Primary fluid inclusion (FI) assemblages in ruby from marble at Mogok and fifteen other deposits from central and Southeast Asia were studied by microthermometry, Raman spectroscopy and crush-leach analysis. Microthermometry combined with Raman spectroscopy investigations of primary FT in Mogok rubies indicated the simultaneous trapping of carbonic FT in the system CO2-H2S (+/- COS +/- S-8) and multi-solid carbonic FI in the system Na-K-Ca-CO3-SO4-NO3-Cl-F +/-(CO2-H2S). The multiple solids are mainly mixtures of Na-Ca-Al carbonates such as shortite and dawsonite, sulphates, phosphates, nitrates, fluorides, and chlorides such as halite. They represent the trapped recrystallised residues of molten salts formed during the metamorphism of evaporite lenses (chlorides and sulphates) intercalated in the carbonate rocks. Raman spectroscopy of solids in FT from all Asian rubies hosted in marbles identified both (i) accidentally trapped minerals mainly calcite, dolomite and rutile, and (ii) daughter phases, i.e., native sulphur, diaspore and boehmite, and Na-K-Ca chlorides, anhydrite, dawsonite, shortite and fluorides. Crush-leach analysis of ruby crystals identified chloride as the dominant anion, but sulphate and nitrate are present at only slightly lower concentrations, whereas they are the dominant species in some Pakistani deposits. The Na-K-Ca-Li-CO3-SO4-NO3-Cl-F molten salt assemblages and the presence of nitrate and phosphate indicate the deposition of the original sediments in a coastal sabkha with ephemeral marine and continental water flooding. Input of V- and Cr-bearing argillite to the salty mudflats insured the formation of rubies in marble during Cenozoic metamorphism.

Electrical conductivity of gabbro: the effects of temperature, pressure and oxygen fugacity

Abstract: The electrical conductivity of gabbro was investigated at 623–1173 K, 0.5–2.0 GPa and oxygen fugacities controlled by three solid buffers (Cu + CuO, Ni + NiO and Mo + MoO 2 ) using a YJ-3000t multianvil press and Solartron-1260 impedance spectroscopy analyzer within the frequency range 10 −1 –10 6 Hz. The measured electrical conductivity shows an Arrhenius increase with temperature and increases with increasing pressure. The activation energy and activation volume of charge carriers have been determined as 0.72±0.01 eV and −6.8 ± 0.69 cm 3 /mol, respectively. The hydrogen-assisted electrical conductivity in gabbro decreases with increasing oxygen fugacity. Furthermore, it is inferred that some hydrogen-related defects with minor concentration ( e.g ., H′ M or H • ) are the main charge carriers in the sample and provide reasonable explanations for the behavior of electrical conductivity of gabbro at high pressure.

Mayenite supergroup, part IV: Crystal structure and Raman investigation of Al-free eltyubyuite from the Shadil-Khokh volcano, Kel’ Plateau, Southern Ossetia, Russia

Abstract: Eltyubyuite, ideally Ca 12 Fe 3+ 10 Si 4 O 32 Cl 6 , a member of the mayenite supergroup, was originally described from altered xenoliths of the Upper Chegem, northern Caucasus, Russia, and Eifel, Germany, where it forms a solid-solution with wadalite (Ca 12 Al 10 Si 4 O 32 Cl 6 ). The structure of the holotype was confirmed earlier using electron backscatter diffraction. The larger crystal size of Al-free eltyubyuite from a new occurrence in an altered carbonate–silicate xenolith enclosed in plagiodacites of the Shadil-Khokh volcano, Kel’ Plateau, Southern Ossetia, enabled the first direct refinement of the eltyubyuite crystal structure. At this locality, Al-free eltyubyuite occurs in a contact zone of the xenolith, within small veins composed of rusinovite, cuspidine and rondorfite. The structure of the Al-free eltyubyuite crystal (dimensions: 20 × 15 × 10 μm) was refined from X-ray diffraction data to R 1 = 0.019. Eltyubyite (cubic, space group I 4 ¯ 3 d , a = 12.2150 (2) A, V = 1822.55(6) A 3 , Z = 2) is isostructural with mayenite. Both tetrahedral are Fe 3+ -dominant: the T 1 site (= 1.848 A) contains 0.85 Fe 3+ and 0.15 Si 4+ , whereas the T 2 site (= 1.766 A) has 0.59 Fe 3+ and 0.41 Si 4+ . Based on electron microprobe data, the empirical formula of eltyubyuite from Ossetia is Ca 12.044 (Fe 3+ 10.373 Si 3.473 Ti 4+ 0.067 Mn 2+ 0.021 Mg 0.021 ) ∑13.956 O 32 Cl 5.455 . Raman spectroscopy recorded bands with increased half-width due to Fe 3+ and Si 4+ disorder at the two tetrahedral sites T 1 and T 2. The Raman bands at 959 and 901 cm −1 have been assigned to Si–O stretching vibrations ( v 1 and v 3 ) of (SiO 4 ) 4− . The group of bands at 783 ( v 3 ), 705 ( v 1 ), 450 ( v 4 ), 307 ( v 2 ) cm −1 correspond to Fe–O vibration of (Fe 3+ O 4 ) 5− .

New zinc and potassium chlorides from fumaroles of the Tolbachik volcano, Kamchatka, Russia: mineral data and crystal chemistry. I. Mellizinkalite, K3Zn2Cl7

Abstract: The new mineral flinteite, ideally K2ZnCl4, was discovered in active fumaroles at two scoria cones of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. In the Northern fumarole field at the First scoria cone (locality of the holotype), flinteite is a common mineral associated with halite, sellaite, fluorite, saltonseaite, chubarovite and hollandite. In the Arsenatnaya fumarole at the Second scoria cone, flinteite occurs with langbeinite, aphthitalite, fluoborite, sylvite, halite, tenorite, hematite, zincite, chubarovite, krasheninnikovite, vanthoffite, etc. In the Glavnaya Tenoritovaya fumarole (Second scoria cone), flinteite is associated with mellizinkalite, belloite, avdoninite, eriochalcite, sylvite, halite, mitscherlichite, sanguite, chrysothallite, romanorlovite, gypsum, chlorothionite, kainite, etc. Flinteite typically forms prismatic crystals up to 0.2 × 0.3 × 1.2 mm, their groups, granular aggregates or crusts up to 0.5 × 5 × 5 mm. The mineral is light green, light yellow to bright greenish-yellow or colourless. It is transparent, with vitreous lustre. Flinteite is brittle, one direction of distinct cleavage was observed. The Mohs hardness is ca. 2. Dcalc = 2.49 g cm−3. Flinteite is optically biaxial (+), α = 1.573(1), β = 1.574(1), γ = 1.576(1), 2 V meas = 40(25)°. The chemical composition of the holotype (wt%, electron-microprobe data) is: K 24.97, Tl 5.82, Co 0.07, Zn 22.23, Cl 46.95, total 100.04. The empirical formula calculated based on the sum of all atoms = 7 pf u is: (K1.91Tl0.09)Σ2.00Zn1.04Cl3.96. Some samples show the following substitutions for K (wt%): up to 27.7 Tl, 0.6–2.4 Rb, 0.5–2.2 Cs. Flinteite is orthorhombic, Pna 21, a = 26.8090(10), b = 12.4085(6), c = 7.2512(3) A, V = 2412.18(18) A3 and Z = 12. The strongest reflections of the powder X-ray diffraction pattern [ d ,A( I )( hkl )] are: 6.23(27)(011, 020), 5.123(88)(311, 320), 3.629(98)(611, 002), 3.599(100)(031), 3.133(35)(022), 3.039(26)(630), 2.897(35)(910) and2.688(46)(911, 920). The crystal structure, solved from single-crystal X-ray diffraction data ( R = 0.0686), contains three Zn sites centring isolated ZnCl4 tetrahedra and six independent K sites. Flinteite is the natural analogue of a well-known synthetic room-temperature modification of K2ZnCl4, a ferroelectric material. The mineral is named in honour of the Russian crystallographer Evgeniy E. Flint (1887–1975).

Phase relations in the K2CO3–FeCO3 and MgCO3–FeCO3 systems at 6 GPa and 900–1700°C

Abstract: The phase relations in the K 2 CO 3 –FeCO 3 system were studied in multianvil experiments using graphite capsules at 6 GPa and 900–1400°C. Subsolidus assemblages comprise the stability fields of K 2 CO 3 + K 2 Fe(CO 3 ) 2 and K 2 Fe(CO 3 ) 2 + siderite with the transition boundary at X (K 2 CO 3 ) = 50 mol%. The K 2 CO 3 –K 2 Fe(CO 3 ) 2 and K 2 Fe(CO 3 ) 2 –FeCO 3 eutectics are established at 1100°C and 65 mol% and at ~1150°C and 46 mol% K 2 CO 3 , respectively. Siderite is a subliquidus phase at 1400°C at X (K 2 CO 3 ) 2 CO 3 –MgCO 3 system, which has two eutectics at 1200°C and 74 mol% and at 1250°C and 48 mol% K 2 CO 3 , respectively. The natural siderite used in the present study contained 6 mol% MnCO 3 and 7 mol% MgCO 3 . Although the obtained Fe-bearing carbonate phases exhibit uniform Mn/(Fe + Mn + Mg) ratio, magnesium tends to redistribute into the solid phases K 2 Fe(CO 3 ) 2 or siderite. At 1200°C and X (K 2 CO 3 ) = 50 mol%, the K 2 Fe 0.88 Mn 0.06 Mg 0.06 (CO 3 ) 2 melt coexists with the K 2 Fe 0.78 Mn 0.06 Mg 0.16 (CO 3 ) 2 compound. Assuming continuous solid solution between K 2 Fe(CO 3 ) 2 and K 2 Mg(CO 3 ) 2 , the K 2 Fe(CO 3 ) 2 end-member should melt congruently slightly below 1200°C, which is about 50° lower than the melting point of K 2 Mg(CO 3 ) 2 . The siderite–magnesite system was studied at 6 GPa and 900–1700°C. Complete solid solution is recorded between Fe 0.94 Mn 0.06 CO 3 siderite and magnesite. At X (MgCO 3 ) = 7 mol% and 1600°C, the (Fe 0.90 Mn 0.06 Mg 0.04 )CO 3 partial melt coexists with (Fe 0.86 Mn 0.06 Mg 0.08 )CO 3 siderite, whereas at X (MgCO 3 ) = 26 and 35 mol%, the (Fe 0.71 Mn 0.06 Mg 0.23 )CO 3 partial melt coexists with (Fe 0.51 Mn 0.06 Mg 0.43 )CO 3 siderite. Based on these data, Fe 0.94 Mn 0.06 CO 3 siderite should melt slightly below 1600°C, i.e . 300° lower than magnesite. Development of bubbles in the quenched melt at X (MgCO 3 ) = 7 mol% and 1700°C suggests incongruent melting of siderite according to the reaction: siderite = liquid + CO 2 fluid.

Three new alluaudite-like protonated arsenates: NaMg3(AsO4)(AsO3OH)2, NaZn3(AsO4)(AsO3OH)2 and Na(Na0.6Zn0.4)Zn2(H0.6AsO4)(AsO3OH)2

Abstract: Three new arsenates, NaMg 3 (AsO 4 )(AsO 3 OH) 2 ( 1 ), NaZn 3 (AsO 4 )(AsO 3 OH) 2 ( 2 ) and Na(Na 0.6 Zn 0.4 )Zn 2 (H 0.6 AsO 4 ) (AsO 3 OH) 2 ( 3 ), were synthesised under low-temperature hydrothermal conditions. 1 is the first example of a synthetic hydrous Na-Mg arsenate, and 2 and 3 are the first synthetic hydrous Na-Zn arsenates with octahedrally coordinated Zn atoms. They are all isostructural with the protonated members of the alluaudite-supergroup compounds; 2 is synthetic end-member of o’danielite. Their crystal structures were determined from the single-crystal X-ray diffraction data collected at 293 K [space group C 2/ c , a = 11.972(2)/12.023(2)/12.458(3), b = 12.367(3)/12.385(3)/12.484(3), c = 6.743(2)/6.750(2)/6.839(2) A, β 112.67(3)/112.79(3)/113.83(3)°, V = 921.3(4)/926.7(4)/973.0(4) A 3 , Z = 4, for 1 , 2 , and 3 respectively]. The crystal structures consist of chains of edge-sharing M 1O 4 (OH) 2 and M 2O 6 octahedra ( M 1, M 2 = Mg for 1 , M 1, M 2 = Zn for 2 , and M 1 = Na, Zn, M 2 = Zn for 3) stacked parallel to (101) and connected by the AsO 4 tetrahedra. These chains form two types of channels parallel to the c -axis. While hydrogen atoms of the OH groups are situated in the channels of the first type, Na atoms are located in the second-type channels. Infrared and single-crystal Raman spectra were measured and evaluated in order to obtain further information on the anion groups and especially on the short hydrogen bonds. The OH stretching frequency is in good agreement with the observed O⋯O distances. Furthermore, the crystal chemistry of synthetic alluaudite-like arsenates is discussed in terms of structure distortion and measure of similarity among them.

Evolution of OH groups in diopside and feldspars with temperature

Abstract: Using in situ FTIR and heating/cooling stage, we have investigated the temperature evolutions of OH bands in natural diopside, plagioclase and anorthoclase. The frequencies of three main resolved OH bands (3645, 3464 and 3361 cm −1 called band 1, 2 and 3, respectively) in diopside shift linearly with temperature. With increasing temperature, band 1 shifts to lower wavenumbers, band 2 exhibits almost no shift while band 3 shifts to higher wavenumbers. The integral absorbance of band 1, 2 and 3 decreases by 18.8, 10.1 and 31.4 %, respectively, from −50 to 400°C. No simultaneous growth and decline of OH bands is observed during the whole process, excluding H proton transfer. In contrast to OH defects in diopside, the bands at lower frequencies in feldspars weaken while their bands at higher frequencies strengthen with increasing temperature, indicating H protons change positions in the crystal structure from one site with stronger H bond to another site with weaker H bond. These results reflect different local environments of OH defects and temperature dependent OH absorption coefficients in diopside, and change of H sites in feldspar structure with temperature. It provides important constraints on the microscopic mechanisms of hydrogen incorporation in these minerals.

Conservation studies of cultural heritage: X-ray imaging of dynamic processes in building materials

Abstract: High-resolution X-ray computed tomography (HRXCT) is a 3 D -imaging and analysis technique frequently used for the investigation of internal structures of a large variety of objects, including building materials. The 3 D information is important for the characterisation of internal dynamic processes ( e.g ., water and salt migration, the influence of temperature and/or relative humidity changes) in natural stone, mortars, bricks and concrete. One of the main advantages of HRXCT is the fact that it is a non-destructive characterization technique, which allows 3 D monitoring of internal structural changes at resolutions in the (sub)micrometre scale. Because of its non-destructive nature, it is possible to measure changes in porosity, evolution of micro-cracks, crystallization of salts and migration paths of liquids in the same rock sample over a specific time period. Driven by the technological and computational progress, the technique is continuously growing as an analysis tool in the Geosciences and is becoming an important method in the field of Cultural Heritage. In this manuscript, a short summary of the principle, the advantages and limitations of X-ray computed tomography are presented. In addition, an overview of some current applications of imaging dynamic processes (such as liquid migration, artificial stone weathering and treatment) is provided by means of HRXCT. This is demonstrated in studies related to conservation of Cultural Heritage.

Multi-methodological study of palaeo-Christian glass mosaic tesserae of St. Maria Mater Domini (Vicenza, Italy)

Abstract: This study focuses on polychrome glass tesserae from the palaeo-Christian mosaic, still in situ , which decorates the vaults of the votive chapel of St. Maria Mater Domini in Vicenza (Veneto region, NE Italy). Aims are characterisation of the “base composition” of the glassy matrix and identification of opacifiers and colourants and these are performed by means of a multi-methodological approach (SEM-EDS, EMPA, XRPD, IS). Systematic comparisons between the Vicenza tesserae and those from the votive chapel of St. Prosdocimus in Padova, part of the remains of the only other palaeo-Christian mosaic located in the Veneto, coeval in age and with comparable colour palettes, are also carried out in order to improve our knowledge of production technologies of these materials during the 6th century AD in the Northern Adriatic area. Textural, chemical, diffractometric and spectroscopic data indicate multiple production technologies in the Vicenza tesserae , with evidence of several glassy matrices, opacifiers/pigments and/or ionic colourants/decolourants, all variously mixed in order to obtain the desired shades. In particular, the matrices of the Vicenza tesserae , mostly comparable with compositional reference groups typical of both Roman and Late Roman times, and opacifiers/pigments mainly composed of antimony-based compounds typical of Roman tradition, indicate the extensive availability of older glass for re-use and/or a preference for recycling, rather than the preparation of new batches. Peculiar is also the finding, in one Vicenza Aquamarine sample, of an opacifier composed of sodium antimonate, never found in ancient glass tesserae until now. Comparisons between the Vicenza and Padova mosaics indicate technological connections between the sites, as testified by the many chromatic groups with high degree of comparability. However, when differences are observed into chromatic groups compared, the Vicenza tesserae generally show older technological features than those of Padova. The hypothesis advanced here, related to the different geographical location of the two sites, explains such experimental evidence in terms of the different speeds at which innovative technologies spread in north-eastern Italy.

Mayenite supergroup, part II: Chlorkyuygenite from Upper Chegem, Northern Caucasus, Kabardino-Balkaria, Russia, a new microporous mineral with “zeolitic” H2O

Abstract: The new mineral chlorkyuygenite, Ca 12 Al 14 O 32 [(H 2 O) 4 Cl 2 ] ( I 4 ¯ 3 d , a =12.0285(1)A, V =1740.34(3)A 3 ), was discovered as an accessory mineral in Ca-humite zones of calcareous skarn xenoliths in ignimbrites of the Upper Chegem Caldera, Northern Caucasus, Kabardino-Balkaria, Russia. Rounded grains and crystals with tris-tetrahedral form of chlorkyuygenite up to 50μm and aggregates up to 100–150μm in size are enclosed in chegemite, reinhardbraunsite and srebrodolskite. Chlorkyuygenite also forms rims on wadalite crystals. Chegemite–fluorchegemite, reinhardbraunsite–kumtyubeite, rondorfite, hydroxylellestadite, lakargiite, perovskite, kerimasite, elbrusite, ettringite-group minerals, hydrocalumite, bultfonteinite, and minerals of the katoite–grossular series are associated with chlorkyuygenite. Larnite, spurrite and galuskinite are noted as relics in Ca-humites. Chlorkyuygenite is colourless, occasionally with a greenish or yellowish tint, and the streak is white. The mineral is transparent with strong vitreous lustre, it is isotropic, n =1.672(1) (589 nm). The microhardness VHN load 50 g is 632(37) kg mm −2 , corresponding to 5–5½ hardness according to the Mohs scale; the calculated density is 2.941 g cm −3 . The calculated Gladstone-Dale’s compatibility factor 1–(K p /K c )=−0.016 is superior. The holotype specimen of chlorkyuygenite from the chegemite zone is characterized by relatively constant composition corresponding to the crystal-chemical formula Ca 11.979 (Al 12.986 Fe 3+ 0.823 Si 0.179 Ti 4+ 0.033 ) ∑14.021 O 32 [(H 2 O) 3.767 Cl 2.234 ] ∑6 . In the Raman spectra of chlorkyuygenite the following characteristic main bands are distinguished: 202, 321, 511, 705, 776 and 881 cm −1 . A broad band with two maxima near 3400 and 3200 cm −1 is observed in the OH region and it is related to H 2 O in the structural cages of chlorkyuygenite. The molecular water is completely released from the mineral structure at about 550°C. Chlorkyuygenite crystallized initially as chlormayenite, which later was altered under influence of volcanic gases containing water vapour.

Crystal chemistry of cation-exchanged forms of epistolite-group minerals. Part II. Vigrishinite and Zn-exchanged murmanite

Abstract: The crystal structure of vigrishinite, an epistolite-group heterophyllosilicate with essential Zn, has been reinvestigated, the ideal end-member formula is revised to Zn 2 Ti 4− x (Si 2 O 7 ) 2 O 2 (OH,F,O) 2 (H 2 O,OH,□) 4 with x 4 solution at 90°C have been obtained from single-crystal X-ray diffraction data. The structural formulae are [ B 1] Ca 0.04 {Na 1.22 (Ti 1.19 Mn 0.60 Nb 0.21 )}{ [ A 1, A 2] Zn 1.03 (Ti 1.64 Nb 0.36 )[Si 2 O 7 ] 2 }O 2 (O,OH) 2 (H 2 O) 4 for vigrishinite and {Na 1.14 (Ti 1.45 Mn 0.50 Nb 0.05 )}{ [ A 1] Ca 0.77 [ A 2] Zn 0.13 (Ti 1.85 Nb 0.15 )[Si 2 O 7 ] 2 }O 2 (OH,O) 2 (H 2 O) 4 and [ B 1] Zn 0.15 [ B 2] Ca 0.18 {Na 1.06 (Ti 1.32 Mn 0.60 Nb 0.08 )}{ [ A 1] Zn 0.70 [ A 2] Ca 0.12 (Ti 1.74 Nb 0.26 )[Si 2 O 7 ] 2 }O 2 (OH,O) 2 (H 2 O) 4 for the 5 and 24 hour Zn-exchanged forms of murmanite, respectively (braces give successively the contents of the octahedral O and heteropolyhedral H sheets). The triclinic ( P −1) unit-cell parameters are respectively: a = 8.7127(17), 8.871(3), 8.748(2) A; b = 8.6823(17), 8.844(6), 8.724(2) A; c = 11.746(2), 11.734(6), 11.675(3) A; α = 91.481(4), 92.75(3), 92.503(13)°; β = 98.471(4), 97.60(4), 97.846(13)°; γ = 105.474(4), 106.23(2), 105.875(13)°; V = 845.0(3), 872.7(8), 845.9(4)A 3 . Our data (1) confirm that vigrishinite was formed as a result of natural ion-exchange of murmanite Na 4 Ti 4 (Si 2 O 7 ) 2 O 4 · 4H 2 O with Zn 2+ in low-temperature solutions; (2) prove that direct transformation of lomonosovite Na 4 Ti 4 (Si 2 O 7 ) 2 O 4 · 2Na 3 PO 4 into vigrishinite, without prior leaching of Na + and PO 4 3− from the former and formation of murmanite, is unlikely; (3) suggest the following ion-exchange mechanism: during the early stage Na + leaches into the solution whereas Ca 2+ , a common admixture in murmanite, migrates into one of the sites in the H sheet, leaving another site vacant for further entry of Zn; in the next stage Zn 2+ enters the emptied site in the H sheet and, in small amount, into the interlayer whereas Ca 2+ partly moves from the H sheet into the interlayer. (4) The data show the transformation of the murmanite-type unit cell ( P −1; V ≈ 440 A 3 ) into the vigrishinite-type cell with a and b parameters corresponding to the ab face diagonals of the former during the first stage of the exchange with Zn, due to ordering in the H sheet. New findings of vigrishinite in two pegmatites of the Lovozero massif, Kola peninsula, Russia (at Severnyi open pit, Mt. Alluaiv, and at Pegmatite #60, Mt. Karnasurt) in the same setting as at the type locality, i.e . only in close contact with cavities after dissolved sphalerite, show that the ion exchange in epistolite-group heterophyllosilicates is not uncommon in Nature. Our data indicate there is a continuous solid solution between murmanite and vigrishinite.

On the deformation mechanism of olivine single crystals at lithospheric temperatures: an electron tomography study

Abstract: We present an electron tomography study of dislocations in deformed olivine single crystals, at ca . 0.5 T m , along two distinct orientations. The easiest slip systems are [001](100) and [001]{110}. Disorientating a single crystal away from easy glide conditions leads to massive cross-slip, which generates three-dimensional dislocations, and thus contributes to hardening. Fast motion of curved non-screw dislocation in those planes leaves long straight screw dislocations which bear lattice friction and control plastic strain. We have identified several hardening mechanisms. Non-screw [001] dislocations interact elastically to form dipoles. Recovery mechanisms leading to dipole annihilation are observed, but they are slow at those temperatures and produce numerous sessile loops. These loops represent obstacles for gliding dislocations. Interactions between dislocations and sessile loops produce sessile segments (super jogs), which efficiently impede dislocation motions.

Rare-earth, yttrium and zirconium mobility associated with the uranium mineralisation at Okrouhlá Radouň, Bohemian Massif, Czech Republic

Abstract: The mobility of rare-earth elements (REE), Y and Zr during the Late-Variscan and post-Variscan mineralisation event in the Okrouhla Radouň uranium deposit has been investigated to elucidate their behaviour during the hydrothermal alteration of leucogranites and high-grade metamorphic rocks in the Moldanubian Zone (Bohemian Massif). The alteration of leucogranites has caused enrichment in Na, Ca, Fe 3+ , Zr and the bulk of REE while depleting K, Fe 2+ , Si, Th, Rb and Ba. The alteration of high-grade metasediments has also led to an enrichment in Na and Ca while depleting K, Si, Rb and Ba. However, this change is connected to the depletion of REE, as well as the enrichment of P and Th in the bulk. The high mobility of Y and Zr during formation of the uranium mineralisation is supported by the occurrence of Y- and Zr-rich coffinite (up to 3.4 wt.% Y 2 O 3 and 13.8 wt.% ZrO 2 ). The massive hydrothermal alteration of host rocks, as well as the high mobility of REE, Y and Zr indicate an influx of oxidised basinal fluids in the Permian to the crystalline rocks of the Moldanubian Zone.

Experimental investigation of the effect of Ca, Fe and Ti on cotectic compositions of the rhyolitic system

Abstract: The effect of the normative anorthite content on the position of cotectic curves in the Qz–Ab–Or–An system has been investigated at 200 MPa and a water activity of 0.5. To simulate compositions as close as possible to those of natural high-silica rhyolites, all investigated compositions also contained ~ 1 wt% FeO and 0.2 wt% TiO 2. The position of the cotectic curves was deduced from crystallization experiments carried out between 790 and 850°C and using fourteen starting glass compositions containing ~ 3 wt% H 2 O. The liquidus phase of the different starting materials was used to constrain the primary fields of quartz, plagioclase and sanidine. The compositions of residual melts coexisting with solid phases were used to define the position of cotectic curves. Compared to the haplogranite system, the eutectic point is shifted away from the Ab apex, and its composition is estimated to be Qz 42 Ab 21 Or 37 when projected onto the haplogranite system. The implications for the estimation of the depth of magma storage conditions are discussed on the basis of an example from the Snake River Plain high-silica rhyolites.