Pseudohexagonal Crystals Research Articles

Highly Tribo-Positive Nylon-11 Film Fabricated by Multiscale Structural Regulation through a Roll-to-Roll Processing.

Triboelectric polymers have attracted extensive attention due to their great electron-accepting and electron-donating properties in contact electrification as well as their flexible and low-cost merits and have become promising electrode materials in triboelectric nanogenerators (TENGs). However, most research has exclusively focused on improving the electron capture capability of the triboelectric layer, neglecting to enhance the electron-donating capability, which leads to a low output performance of TENG and limits its practical application. In this study, we developed a method to fabricate highly tribo-positive Nylon-11 film through roll-to-roll processing. Paired with the poly(tetrafluoroethylene) triboelectric layer, the transferred charge density of contact-separation TENG based on Nylon-11 film prepared by this method reaches 291.1 μC/m2, which has been improved by 12.4% compared with the conventional compression molding sample. The novel fabricating method can regulate the surface functional groups to achieve higher surface potential and obtain a favorable pseudohexagonal crystal phase, leading to an increasing transferred charge density in triboelectrification. Additionally, it has been analyzed that higher chemical potential of materials can facilitate the transfer of electrons from the triboelectric polymer surface. This study provides a nonadditive, simple, and effective strategy to fabricate excellent tribo-positive material, which can significantly enhance the performance of TENG.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 3. Mineralogy of lithium-bearing objects: feldspars

Traditionally, feldspars are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — kamyano-mohyla (stone grave) complex of Azov region — Kruta Balka rare-metal deposit — Shevchenkivske rare-metal deposit — rare-metal pegmatites of Inhulsky megablock. Feldspars in the chamber pegmatites of the Volyn are represented by maximum microcline-perthite, rarely by intermediate orthoclase and albite. Widely developed feldspars with close regularity, but different symmetry. The form of discharge is granular aggregates and polyhedral crystals. The outline of potassium feldspar crystals is varied. Crystals of only two morphological types have a clear arrangement: I — early high-temperature bar-like individuals, concentrated in the cavities of the graphic zone; II — columnar pseudohexagonal crystals in sinkholes. Among albite crystals, three morphological types are distinguished, depending on acidity-alkalinity and crystallization temperature. Feldspars of chamber pegmatites are well studied by radio spectroscopic, luminescent and genetic methods. Within the boundaries of the Perzhansky ore complex, multi-grained polygenic microcline-perthite dominates, the structural state of its potassium phase corresponds to a high degree of ordered distribution of Si and Al (maximum microcline). The evolution of the twin structure of potassium feldspars is briefly covered and illustrated. Pure microcline and amazonite (probably the purest on the Ukrainian Shield) were found in the perzhansky metasomatites. Feldspars are the leading minerals of the stone-burial complex of the Azov region, represented by microcline and microcline-perthite. A characteristic feature of the microcline rocks of the complex is the unique giant dendritic crystals of pink microcline. Feldspars in the Kruta Balka rare metal deposit are represented by albite, albite-oligoclase and microcline. Two feldspars — microcline and albite (in the form of perthites in microcline and independent aggregates) were diagnosed in the Shevchenkivske deposit. Microcline makes up 15-20% of the volume of pegmatites and represented by three generations. The mineralogy of feldspars in the pegmatites of the Inhulsky megablock is different. They are represented by monoclinic orthoclase, microcline and plagioclase (mostly albite, occasionally oligoclase). Their content in rocks is mostly >50%, but albite >potassium feldspar. In general, these feldspars have features uncharacteristic of rare-metal pegmatites: 1) high symmetry (monoclinic) and low order (t1 >0,7); 2) microperthite decay structure; 3) the initial and middle stages of monodomainization are manifested. These and other features of minerals are a consequence of the specific origin of pegmatites, which represent a new genetic type of deposits of rare elements — metapegmatites.

Diagenetic Origin of Bipyramidal Quartz and Hydrothermal Aragonites within the Upper Triassic Saline Succession of the Iberian Basin: Implications for Interpreting the Burial–Thermal Evolution of the Basin

Within the Upper Triassic successions in the Iberian Basin (Spain), the occurrence of both idiomorphic bipyramidal quartz crystals as well as pseudohexagonal aragonite crystals are related to mudstone and evaporite bearing sequences. Bipyramidal-euhedral quartz crystals occur commonly at widespread locations and similar idiomorphic crystals have been described in other formations and ages from Europe, America, Pakistan, and Africa. Similarly, pseudohexagonal aragonite crystals are located at three main sites in the Iberian Range and are common constituents of deposits of this age in France, Italy, and Morocco. This study presents a detailed description of the geochemical and mineralogical characteristics of the bipyramidal quartz crystals to decipher their time of formation in relation to the diagenetic evolution of the sedimentary succession in which they formed. Petrographic and scanning electron microscopy (SEM) analyses permit the separation of an inner part of quartz crystals with abundant anhydrite and organic-rich inclusions. This inner part resulted from near-surface recrystallization (silicification) of an anhydrite nodule, at temperatures that were <40 °C. Raman spectra reveal the existence of moganite and polyhalite, which reinforces the evaporitic character of the original depositional environment. The external zone of the quartz contains no anhydrite or organic inclusions and no signs of evaporites in the Raman spectra, being interpreted as quartz overgrowths formed during burial, at temperatures between 80 to 90 °C. Meanwhile, the aragonite that appears in the same Keuper deposits was precipitated during the Callovian, resulting from the mixing of hydrothermal fluids with infiltrated waters of marine origin, at temperatures ranging between 160 and 260 °C based on fluids inclusion analyses. Although both pseudohexagonal aragonite crystals and bipyramidal quartz appear within the same succession, they formed at different phases of the diagenetic and tectonic evolution of the basin: bipyramidal quartz crystals formed in eo-to mesodiagenetic environments during a rifting period at Upper Triassic times, while aragonite formed 40 Ma later as a result of hydrothermal fluids circulating through normal faults.

New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XIII. Pansnerite, K3Na3Fe3+6(AsO4)8

AbstractThe new mineral pansnerite, ideally K3Na3Fe3+6(AsO4)8, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite, hematite, sanidine, badalovite, khrenovite, achyrophanite, arsenatrotitanite, ozerovaite, tilasite, calciojohillerite, johillerite, nickenichite, svabite, katiarsite, yurmarinite, anhydrite, rutile, cassiterite and pseudobrookite. Pansnerite forms tabular to lamellar (flattened on {010}), usually pseudo-hexagonal crystals up to 0.2 mm × 0.7 mm × 1 mm and crystal clusters up to 2 mm across. It is transparent to translucent, light green, pale greenish, yellowish–greenish or yellowish, with vitreous lustre. The mineral is brittle, with perfect {010} cleavage. The Mohs’ hardness is ca 3. Dcalc is 3.596 g cm–3. Pansnerite is optically biaxial (–), α = 1.702(4), β = 1.713(4), γ = 1.717(4), 2Vmeas = 45(10)° and 2Vcalc = 62°. Chemical composition (holotype, wt.%, electron microprobe data) is: Na2O 6.39, K2O 8.52, CaO 0.08, MgO 0.08, MnO 0.02, NiO 0.02, CuO 1.35, ZnO 0.34, Al2O3 7.35, Cr2O3 0.04, Fe2O3 16.72, SiO2 0.16, P2O5 0.22, V2O5 0.09, As2O5 57.76, SO3 0.04, total 99.20. The empirical formula based on 32 O apfu is K2.86Na3.26Ca0.02(Fe3+3.31Al2.28Cu0.27Zn0.07Mg0.03Cr0.01)Σ5.97(As7.95P0.05Si0.04V0.02S0.01)Σ8.06O32. Pansnerite is orthorhombic, Cmce, a = 10.7372(3), b = 20.8367(8), c = 6.47335(15) Å, V = 1448.27(7) Å3 and Z = 2. The strongest reflections of the X-ray powder diffraction pattern [d,Å(I)(hkl)] are: 10.49(100)(020), 5.380(88)(111), 4.793(65)(220), 3.105(46)(311, 002), 3.079(32)(112, 061), 2.932(35)(260), 2.783(65)(202) and 2.694(52)(400, 222). The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 2.82%. The structure is based on heteropolyhedral layers formed by MO6 octahedra (M = Fe3+ and Al) sharing common vertices and connected by AsO4 tetrahedra. Na+ and K+ cations are located in the interlayer space. The mineral is named in honour of the German–Russian mineralogist and geographer Lavrentiy Ivanovich Pansner (1777–1851). Pansnerite forms a solid-solution series with the isotypic mineral ozerovaite, ideally KNa2Al3(AsO4)4.

The Belterra Clay on the bauxite deposits of Rondon do Pará, Eastern Amazon

ABSTRACT: Bauxite deposits in the Amazon region are commonly covered by yellowish clays which can reach up to 25m thick, known as Belterra Clay (BTC). In Rondon do Para, Eastern Amazon, BTC is 13m thick and covers world-class bauxite reserves. Three pilot bauxite mines were investigated in Rondon do Para for an initial characterization of the local BTC. In discordant contact with the lateritic profile, the BTC has reddish brown colors at its base to ocher tones towards the top. It has a massive structure with silt-clayey texture and nodular bauxitic fragments at its base. Rietveld mineral quantification of the material attests that it is dominated by kaolinite, with goethite, gibbsite, hematite, anatase and residual quartz. The thermal behavior of the material also confirms its mineralogical composition. Kaolinite is of low structural order, which was considered the main difficulty in the application of the Rietveld method. Goethite has up to 33 mol% of Al. As observed by scanning electron microscopy (SEM), the minerals represent pseudo-hexagonal crystals measuring from 150 to 700 nm. The BTC in the studied area is correlated to BTC on others bauxitic deposits of the Amazon region, suggesting this material experienced the same genesis and geological evolution, probably during the Pliocene.

Tiberiobardiite, Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, a New Mineral Related to Chalcophyllite from the Cretaio Cu Prospect, Massa Marittima, Grosseto (Tuscany, Italy): Occurrence and Crystal Structure

The new mineral species tiberiobardiite, ideally Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, has been discovered in the Cretaio Cu prospect, Massa Marittima, Grosseto, Tuscany, Italy, as very rare, light green, vitreous, tabular {0001}, pseudo-hexagonal crystals, up to 200 μm in size and 5 μm in thickness, associated with brochantite. Electron microprobe analysis gave (in wt %, average of 5 spot analyses): SO3 10.37, P2O5 3.41, As2O5 0.05, SiO2 8.13, Al2O3 5.54, Fe2O3 0.74, CuO 62.05, and ZnO 0.03, for a total of 90.32. Based on an idealized O content of 42 atoms per formula unit, assuming the presence of 16 H2O groups and 13.5 cations (without H), the empirical formula of tiberiobardiite is (Cu8.69Al0.21Fe0.10)Σ9.00Al1.00(Si1.51P0.54)Σ2.05S1.44O12.53(OH)13.47·16H2O. The main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 9.4 (s), 4.67 (s), 2.576 (m), 2.330 (m), and 2.041 (mw). The crystal structure study revealed tiberiobardiite to be trigonal, space group R 3 ¯ , with unit-cell parameters a = 10.6860(4), c = 28.3239(10) Å, V = 2801.0(2) Å3, and Z = 3. The crystal structure was refined to a final R1 = 0.060 for 1747 reflections with Fo > 4σ (Fo) and 99 refined parameters. Tiberiobardiite is the Si-analogue of chalcophyllite, with Si4+ replacing As5+ through the coupled substitution As5+ + O2− = Si4+ + (OH)−. The name tiberiobardiite honors Tiberio Bardi (b. 1960) for his contribution to the study of the mineralogy of Tuscany.

Incorporation of silica into the goethite structure: a microscopic and spectroscopic study

Quartz and iron (hydr)oxide are reactive surface phases that are often associated with one another in soils and sediments. Despite the several studies on the coating of quartz with iron oxides, the reactivity of dissolved species (Si) leached from quartz with iron (hydr)oxides has received limited attention. In this study, goethite synthesized on quartz substrates were characterized using field emission scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, and Fourier-transform infrared (FT-IR) spectroscopy. The SEM characterization revealed that bundles of thin parallel aligned goethite rods were formed at pH > 10, while large pseudohexagonal crystals of twinned goethite needles were synthesized at pH ≤ 10 after dehydration and hydration in the alkaline media. TEM analysis showed expanded and distorted lattice spacing of the crystal structure of iron (hydr)oxide due to silica incorporation. The characterization showed that silica increased the crystallite size of the goethite and transformed its acicular texture to a larger, twinned needle structure. FT-IR and XRD analyses revealed band shifts in crystal bonds as well as new bond formations, which indicate the presence of changes in the chemical environment of Fe–O and Si–O bonds. Thus, the presence of sorbed silicates modifies the crystal and lattice structure of goethite.

Weathering profiles and clay mineralogical developments, Bornholm, Denmark

Saprock-saprolite associations were studied by field and laboratory methods (optical microscopy, X-ray powder diffraction, scanning electron microscopy, electron microprobe) in order to describe regolith development in the crystalline rocks of the Nygård kaolin pit (Bornholm, Denmark). The clay sequences and stages of porosity development are similar to those observed for reservoir rocks from the Utsira High (Riber et al., 2016). The weathering of the parent granite began before the end of the Mesozoic. Two stages of syn-/pre-burial alteration, followed by diagenesis during burial, and then post-uplift weathering have been recognized. In stage Ι, plagioclase and some biotite (biotite-vermiculite-kaolinite) reacted to form elongate booklets of highly-ordered kaolinite or smaller, blocky pseudohexagonal crystals. Stage II represented more extreme weathering developed along local fracture systems. The higher potential for fluid flow in the fractures caused highly-ordered kaolinite to alter to halloysitic, poorly-ordered kaolinite. Plagioclase, biotite, and K-feldspar continued to interact with formation water and formed additional quantities of secondary clay minerals. As a consequence of inter-, intra-, and trans-granular cracks, the original rock fabric deteriorated and porosity increased. During later burial, diagenetic siderite crystals filled voids and chlorite formed at the expense of kaolinite. After re-exposure, calcite precipitated in localized zones. Smectite formed on a broader scale wherever high ionic strength groundwaters were present. A mineralogical key to predicting where high porosity and permeability zones occur is the recognition of halloysitic, poorly-ordered kaolinite. Highly-ordered kaolinite is abundant, but it is ubiquitous. Siderite, chlorite and smectite adversely affect permeability.Riber, L., Dypvik, H., Sørlie, R. and Ferrell, R. (2016) Clay minerals in deeply buried paleoregolith profiles, Norwegian North Sea. Clays Clay Miner. DOI: 10.1346/CCMN.2016.064036.

Thermal and kinetic study of hexagonal boric acid versus triclinic boric acid in air flow

Boric acid is a very important inorganic material with diverse uses in optoelectronics, petroleum industry, medicine, agriculture, etc. Recently, it was reported on the modification of the crystallization system of the triclinic boric acid (TBA) to hexagonal boric acid (HBA), when a special obtaining procedure is applied. In this paper, the thermokinetic stability of HBA novel material was comparatively studied with respect to the well-known TBA, in air flow atmosphere. Both HBA and TBA undergo a three-step overall thermal decomposition reaction (dehydration), following similar pathways; from the thermodynamic point of view HBA is more stable—decomposition temperatures and ΔH are higher in this case compared to those of TBA. The kinetic analysis was performed by means of the isoconversional methods, for each step of dehydration observing different thermokinetic regions. Higher thermal stability for HBA enables it to be employed at higher temperatures instead of TBA, explaining why the triclinic symmetry enhances the formation actually of the pseudo-hexagonal crystals as crystal habit at the macroscopic scale. Lower thermodynamic and kinetic stability of HBA makes it easier to be activated and thus more instable at the microstructural scale: this is an indirect proof of the TBA presence in the usual surrounding conditions and in the same time raises the probability for HBA molecules to slide onto their crystalline layers due to the lability of hydrogen bonds keeping them and thus increased potential to intercalate with other molecules. The present results open the possibility for promising applications of HBA as a better lubricant for various industries, while in the medical sector superior cleanser, antifungal and antibacterial properties may be foreseen.

Generation of authigenic clay minerals during diagenesis and their influences on porosity and permeability of Oligocene sandstone reservoir rocks, from a well in the west of Cuu Long basin

Porosity and permeability play a prerequisite role for hydrocarbon reservoirs and fluid flows, especially in sandstone reservoir rocks. The rocks with high porosity decrease down to lower porosity with increasing burial depth due to compaction, cementation and precipitation of authigenic minerals in pores from over saturated solution of minerals. The detailed study of the authigenic clay mineral formation in pore spaces of sandstone reservoir rocks is therefore crucial to estimate the degree of reservoir rock quality. In this study 20 sandstone cores taken from the interval burial depths of 3,700 m - 4,200 m from Oligocene sandstone sequence of a well in the West of the Cuu Long basin, offshore Vietnam, were analyzed by SEM and thin section. Authigenic clay minerals were formed due to temperature and chemistry changes and owing to dissolution of less stable minerals in these burial depths. Authigenic chlorite mineral appears quite abundantly and illite is less frequently. Chlorite was formed from the elements Al and Si, which were released from dissolved grains and Fe and Mg supplied from breakdown of the ferromagnesian minerals of rock fragments and matrix components into pore waters in the burial stage. Illite is associated with the expense of grain dissolution of feldspar, volcanic fragment. Chlorite mostly appears as a coating or mats comprising of small pseudo-hexagonal crystals arranged perpendicular to detrital grain surfaces. Grainrimming chlorites on quartz grain are responsible for the preservation of the porosity in the sandstones because they limit the formation of quartz overgrowth. Additionally fibrous or flaky illite bridging the pores between the grains creates permeability barriers to fluid flows through the sandstones. Thus illite significantly reduces the permeability but to lesser extent affect porosity. Locally, smectite mixes with illite or chlorite and is not abundant in the studied samples. It therefore has no significant impact on the porosity and permeability as well. The variations of the porosity and the permeability of the studied sandstones depend on the generated degree and the arranged patterns of chlorite and illite in pore spaces.

Mapiquiroite, (Sr,Pb)(U,Y)Fe2 (Ti,Fe3+)18O38, a new member of the crichtonite group from the Apuan Alps, Tuscany, Italy

Mapiquiroite, (Sr,Pb)(U,Y)Fe 2 (Ti,Fe 3+ ) 18 O 38 , was identified as a new mineral from the baryte + pyrite + iron oxide ores of Buca della Vena (BdV) and Monte Arsiccio (MA) mines, Apuan Alps, Tuscany, Italy. At BdV, mapiquiroite occurs as complex rhombohedral or tabular pseudo-hexagonal crystals, up to 1 mm in size, black in colour, with a sub-metallic lustre, in quartz + ‘adularia’ + baryte veins embedded in schists, in association with allanite-(Ce), anatase, destinezite, gypsum, monazite-(Ce), pyrite, rutile, and ‘tourmaline’; at MA, mapiquiroite forms tabular pseudo-hexagonal crystals, up to 5 mm in size, in quartz + carbonate veins embedded in magnetite-rich dolostones, in association with baryte, boulangerite, derbylite, siderite, and sphalerite. Under the microscope, mapiquiroite is blackish in colour, weakly bireflectant, and non-pleochroic. Internal reflections are absent. Anisotropism is distinct, without characteristic rotation tints. Minimum and maximum reflectance data for COM wavelengths [λ (nm), R air (%); data for the specimens from BdV and MA, respectively] are: 471.1, 17.0/17.2 and 17.7/18.0; 548.3, 16.7/17.0 and 17.6/17.8; 586.6, 16.4/16.7 and 17.3/17.7; 652.3, 16.1/16.3 and 17.0/17.3. Vickers hardness is 750 kg · mm −2 and 782 kg·mm −2 for specimens from BdV and MA, respectively, corresponding to a Mohs’ hardness ~ 6. The chemical data point to the formulae (Sr 0.533 La 0.176 Pb 0.105 Na 0.030 Ca 0.026 ) ∑=0.870 (U 0.407 Ce 0.101 Y 0.205 Mn 0.072 ) ∑=0.785 Fe 3+ 2.000 (Ti 12.423 Fe 3+ 3.345 Cr 1.624 V 5+ 0.129 Al 0.032 Sn 0.013 Nb 0.007 ) ∑=17.573 O 38 (BdV) and (Sr 0.312 Pb 0.248 Na 0.019 Ca 0.014 La 0.009 ) ∑=0.602 (U 0.858 Y 0.070 Ce 0.021 Mn 0.005 ) ∑=0.954 (Fe 3+ 1.695 Zn 0.305 ) ∑=2.000 (Ti 12.070 Fe 3+ 4.987 V 5+ 0.372 Al 0.030 Nb 0.030 Cr 0.015 Sn 0.001 ) ∑=17.505 O 38 (MA). Mapiquiroite is trigonal, R 3, with a 10.3719(7), c 20.875(1) A, V 1944.8(2) A 3 and a 10.3854(3), c 20.8942(6) A, V 1951.7(1) A 3 for the specimens from BdV and MA, respectively. The crystal structures of mapiquiroite from these two occurrences were refined to R 1 = 0.028 and 0.032, respectively. Mapiquiroite is isostructural with other members of the crichtonite group. The name mapiquiroite honours four Italian mineral collectors, Riccardo Mazzanti, Luigi Pierotti, Ugo Quilici, and Moreno Romani for their contribution to the study of the mineralogy of baryte + pyrite + iron oxide deposits from the Apuan Alps.

Lithostructural framework and rare metal (Ta-Nb-Sn-Li-Be) mineralisation in lepidolite from the Ijero-Aramoko pegmatite field, south-western Nigeria

A lithological framework and petrochemical features relating to Ta-Nb-Sn-Li-Be mineralisation in lepidolite from the Ijero-Aramoko pegmatite field, south-western Nigeria were investigated. Systematic geological mapping revealed that the pegmatite occurs as steeply inclined intrusive bodies in a basement of gneisses and schistose assemblages that are occasionally pulsed with isolated granitic bodies. The lepidolite occurs in the intermediate (coarse-grained microcline-albite-quartz) zone of the inclined complex pegmatite. The lepidolite has a layered structure, tabular pseudo-hexagonal crystals with scaly aggregates of perfectly cleavable masses and an equigranular texture. The major and trace element composition of 30 lepidolite samples was determined using inductively coupled plasma–atomic emission spectrometry with a view to determining compositional features relating to Ta-Nb-Sn-Li-Be mineralisation. The average silica content of the lepidolite ranged from 49.43% to 57.81%. The three sampling localities and their mean SiO2 contents were Oke-Asa (c. 49.83%), Oke-Igbo Aba (c. 49.99%) and Ijero-Ekiti (c.58.40%). Average Al2O3 content was 27.83%, 23.02% and 28.34%, respectively. Similarly, K2O content was 10.06%, 9.41%, and 5.86%, respectively. The contents of MgO, CaO and TiO2 collectively contributed less than 0.5% to the minerals bulk composition. Trace element composition revealed enrichment in Li, Be, Cs and Rb, relative to Ta, Nb and Sn. Lepidolite from Oke Asa, Oke Igbo Aba and Ijero-Ekiti contained an average Li content of 1 859 ppm, 1 778 ppm and 1 656 ppm, respectively. Similarly, the average Ta content was 0.36 ppm, 0.6 ppm and 0.03 ppm, respectively, and Nb and Sn contents showed a similar trend. The Li content of lepidolite from Ijero-Aramoko pegmatite fields is marginally less than the 2% threshold value required for its use as an ore of Li. However, the low Li content of the mineral qualifies it for use in pharmaceuticals, glass, alloy, Li storage batteries and smelting of Al ore and other industrial applications requiring a low Li content.

A comparison of properties of clay minerals in isalteritic and in degraded facies

AbstractThe mineralogical, geochemical and micromorphological features of an isalteritic clay facies, which originated from weathering of an anorthosite, were compared to those of clay facies derived from the degradation of a bauxite developed from the same rock. The isalteritic clay was formed by the hydrolytic alteration of plagioclase, whereas the degraded clays were formed by decomposition of gibbsite and neoformation of kaolinite. This resilification process resulted from the reintroduction of silica via the oscillation of the phreatic level and/or the decomposition of organic matter on the surface. The degradation process was gradual and yielded two different facies: (a) degraded clays with almost total decomposition of gibbsite, and (b) degraded clays with gibbsite nodules. Morphologically, the isalteritic clays differ from the degraded clays because they contain larger hexagonal and pseudo-hexagonal crystals. The degraded clays have more irregular crystal shapes, ranging from laths to anhedral shapes.

Comparative influence of burial depth on the clay mineral assemblage of the Agadir-Essaouira basin (western High Atlas, Morocco)

AbstractIn the western High Atlas basin, the evolution of the clay assemblage of the Upper Jurassic–Cretaceous sedimentary series is controlled by palaeogeographic changes of the basin and by burial diagenesis.The effects of burial are expressed by an increase in the proportions of illite and chlorite with depth, a decrease of expandability of smectite minerals and by a decrease in the Kübler Index.Kaolinite is preserved at greater depths than smectite, but also tends to diminish in abundance. TEM observations show that idiomorphic pseudo-hexagonal crystals of illite increase in size and abundance downwards, especially in the sandy levels.In the Agadir section, the main change in the clay mineral evolution related to late diagenesis occurs at the Mid-Albian, corresponding to a burial depth of about 1800 m; in the Essaouira section it occurs at the Lower Tithonian at a burial depth of about 2100 m.Considering the different geothermal gradient between Agadir (36ºC km–1) and Essaouira (27ºC km–1), the disappearance of smectite occurs at the same temperature in these two sites (60 to 65ºC).

Two crystal modifications of (Pro-Pro-Gly)4-Hyp-Hyp-Gly-(Pro-Pro-Gly)4reveal the puckering preference of Hyp(X) in the Hyp(X):Hyp(Y) and Hyp(X):Pro(Y) stacking pairs in collagen helices

Two crystal modifications of a collagen model peptide, (Pro-Pro-Gly)(4)-Hyp-Hyp-Gly-(Pro-Pro-Gly)(4) [where Hyp is (4R,2S)-L-hydroxyproline], showed very similar unit-cell parameters and belonged to the same space group P2(1). Both crystals exhibited pseudo-merohedral twinning. The main difference was in their molecular-packing arrangements. One modification showed pseudo-hexagonal packing, while the other showed pseudo-tetragonal packing. Despite their different packing arrangements, no significant differences were observed in the hydration states of these modifications. The peptide in the pseudo-tetragonal crystal showed a cyclic fluctuation of helical twists with a period of 20 A, while that in the pseudo-hexagonal crystal did not. In these modifications, the puckering conformations of four of the 12 Hyp residues at the X position of the Hyp(X)-Hyp(Y)-Gly sequence were in the opposite conformations to the previous hypothesis that Hyp(X) residues involved in Hyp(X):Hyp(Y) and Hyp(X):Pro(Y) stacking pairs prefer up-puckering and down-puckering conformations, respectively. Detailed investigation of the molecular interactions between Hyp(X) and adjacent molecules revealed that these opposite conformations appeared because the puckering conformation, which follows the hypothesis, is subject to steric hindrance from the adjacent molecule.

Factors governing the formation of lithiophorite at atmospheric pressure

AbstractLithiophorite is a naturally occurring Mn oxide mineral commonly found in soils and sediments. The usual method of synthesizing lithiophorite is via a hydrothermal process in an autoclave at relatively high temperature and pressure. In the present study, an alternative, reflux method, at atmospheric pressure, for synthesis of lithiophorite was developed successfully. The influence of reaction duration, temperature, type of precursor birnessite (H-birnessite, Na-birnessite, aged Na-birnessite), and pH on the formation of lithiophorite were investigated by reflux treatment of lithium-aluminum hydroxide complex ion ( )-exchanged birnessite. The results show that the degree of conversion of lithiophorite decreases with decreasing reaction temperature. Lithiophorite can be obtained at pH values from 5.0 to 9.0, but a circumneutral pH is more favorable for formation at atmospheric pressure. Conversion of Na-birnessite (Bir-OH) to lithiophorite is more favored than aged Na-birnessite (Bir-OH-A). Lithiophorite was not obtained by refluxing the ion-exchanged H-birnessite (Bir-H) sample. The rate of conversion of lithiophorite increases with increasing reflux time. Lithiophorite synthesized by a reflux process has pseudo-hexagonal crystals of 0.1–0.5 µm with a chemical composition of Li0.24Al0.46MnO2.67(H2O)1.25. The results have important implications for the origin and underlying mechanism of lithiophorite formation in the environment.

Fully Inorganic Electrodeposition of Pure Aragonite Prismatic-like Textured Layers on Titanium Foils

This work shows the capabilities of a specific method to synthesize pseudo-hexagonal prismatic-like layers on titanium foils without any organic matrix intervention, in constrast to mollusc shell growth. Using an electrochemical method of deposition, pure aragonite layers are obtained, which exhibit good texture strengths and pseudo-hexagonal crystals. The aragonite crystals grow with the c-axes orthogonal to the titanium foil surface without in-plane orientation, which resembles textures exhibited in nacre layers of some gastropods such as Haliotis haliotis with however lower texture strengths. It turns out that if organic materials can magnify textural characteristics in many aragonite-based layers, the inorganic influence is intrinsically large. This work will serve as a basis for mimicking synthetic hybrid layers by electrochemistry targeting osteoinductivity, with the view of substituting actual biocompatible, but inert, implants, and exemplifies the inorganic role played in the growth process of natural shells.

Origin of the Rio Capim Kaolin based on optical (petrographic and SEM) data

The Ipixuna Formation (late Cretaceous? early Tertiary) exposed in the Rio Capim area, northern Brazil, was subdivided recently into three stratigraphic units, informally known as the lower soft kaolin, the intermediate kaolin, and the upper, endured, semi-flint kaolin. These units had their primary texture and composition strongly modified after deposition. Petrographic and scanning electronic microscopic (SEM) investigation revealed many remaining features that led to relate the soft and the semi-flint kaolin to two depositional sequences. The soft kaolin unit consists of well structured, sub-angular to sub-rounded, and locally angular, sandstones. These are herein designated as kaolinitized sandstones to refer to felspathic sandstones and arkoses where the feldspar grains were replaced by kaolinite. The kaolinitized sandstones are interbedded with either laminated or massive pelites. These lithologies, composed of grains and lithic fragments related to felsic volcanic and meta-volcanic sources, as well as metamorphic and granitic rocks, had their texture and composition strongly modified, resulting in units with an actual wacky nature. Kaolinitization produced three types of kaolinites, categorized according to texture, as Ka, Kb and Kc kaolinites. Ka kaolinite, typical of the sandstones, consists of hexagonal to pseudohexagonal crystals 10–30 μm in diameter, and occurs as agglomerates of booklets or vermicular crystals that reach up to 400 μm in length. Kb kaolinite, which dominates in the mudstones, consists chiefly of hexagonal and pseudohexagonal crystals averaging 1–3 μm in diameter that occur isolated, or as intergrowths of chaotic, face-to face or, less commonly, parallel to pseudo-parallel crystals. Kc kaolinite, which is abundant only in association with paleosols, displays hexagonal to pseudohexagonal crystals with regular sizes around 200 nm in diameter. The semi-flint is attributed to a distinctive depositional unit formed by sediments from variable sources, but with a significant contribution from the underlying soft kaolin. This is suggested by a high volume of sandstones displaying grains that are sub-rounded to rounded and consisting of homogeneous, dark brown masses of kaolinite that are highlighted by films of iron oxides. As opposed to the soft kaolin unit, the semi-flint is dominated by endured Kc kaolinite, which mostly likely results from a combination of weathering during transportation and pedogenesis acting in several phases of sediment subaerial exposure.

Mineralogical characteristics and micromorphological observations of brittle/soft Fe/Mn concretions from Okinawan soils

AbstractManganese minerals are not common and the distinction of poorly crystalline Mn minerals from other associated minerals is important. For many years, the crystal structures of poorly crystalline Mn minerals in Fe/Mn concretions have been the subject of considerable conjecture and controversy. This study reports the micromorphological and mineralogical characteristics, and the chemical composition of Fe/Mn minerals in soft Fe/Mn concretions formed in Shimajiri Mahji soils (Typic Hapludalfs) that developed from Ryukyu limestone on Okinawa Island, Japan. The Fe/Mn minerals in brittle/soft Fe/Mn concretions were characterized using a sequential selective dissolution procedure (SSDP) by treatments with NaOH, hydroxylamine hydrochloride (HAHC) at 25°C and 60°C, and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The HAHC treatment at 25°C dissolved birnessite, but not lithiophorite and goethite. A subsequent extraction with HAHC at 60°C dissolved lithiophorite but not goethite. Finally, the DCB treatment was able to dissolve goethite. The SEM images show that birnessite crystals, with a blade- or plate-like habit, form globular aggregates inside veins and cavities. Pseudo-hexagonal crystals of lithiophorite have produced thread-ball structures with crystal shape similar to birnessite and birnessite crystals are closely associated with lithiophorite. Well developed hexagonal plates of gibbsite crystals are clustered in different directions to make foliated vermiform structures. Aggregates of goethite crystals are acicular and are arranged into stars. The supplementary SSDP, in combination with XRD and SEM techniques, provides methods to distinguish and partly quantify birnessite and lithiophorite in the presence of layer silicate and Fe oxide minerals and confirm their own morphological features.

Synthesis of polyolefins with unique properties by using metallocene‐type catalysts

AbstractCopolymerization of ethylene and 1,5‐hexadiene (HD) by zirconocene catalysts proceeded via cyclization‐addition mechanism to form 1,3‐didsubstituted cyclopentane structure in the polyethylene chain. The 1,3‐cyclopentane structure was found to be taken in the crystalline structure of polyethylene (isomorphism) by partially chainging the trans zigzag chain into gauche conformation, thereby, inducing a transformation of orthorhombic crystal to pseudohexagonal crystal. Copolymerization of ethylene and cyclopentene (CPE) by zirconocene catalysts yielded copolymers having 1,2‐disubstituted cyclopentane structure in the polyethylene chain. The 1,2‐cyclopentane structure was not taken into the crystalline structure of polyethylene. The melting point (Tm) and the crystallinity (Xc) of polyethylene decreased by copolymerization of HD or CPE, and the Tm‐ and Xc‐decreasing effect of CPE was stronger than HD. For copolymers of propylene and HD or CPE obtained with isospecific zirconocene catalyst, the isomorphism was not ovserved.