bluuebunny/crossref_metadata_2025_split huggingface dataset:
A nanopetrographic and textural study of grain-coating chlorites in sandstone reservoirs
Authors: Billault V. , Beaufort D. , Baronnet A. , Lacharpagne J. -C. 
Published: January 2004

AbstractScanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) investigations of chlorite grain coatings from four different sandstone reservoirs indicate a progressive change in both texture and arrangement of chlorite particles from the contact with the detrital substratum to the centre of the pore. Such spatial distribution results from growth by geometrical selection. Geometrical selection of chlorite crystals proceeded during a single event of continuous growth which began before the consolidation of the sandy sediments, lasted through part of the subsequent mechanical compaction and ceased before the occurrence of quartz cement. Nanopetrographic investigations near the detrital quartz-chlorite coating interface demonstrate that inhibition of the quartz cement is due to the limitation of the epitaxial growth of quartz to the interparticular space at the base of the chlorite coating and not an absence of nucleation. It is suggested that these results can be applied to most of the sandstones which contain Fe-rich chlorite grain coatings.
Effect of acid treatment on the structure of sepiolite
Authors: Yebra-Rodríguez A. , Martín-Ramos J . D. , Del Rey F. , Viseras C. , López-Galindo A. 
Published: January 2004

AbstractAn ab initio determination of the structure of sepiolite after acid treatment (HCl 0.5 N for 24 h) was carried out using X-ray powder diffraction data. After acid treatment, the sections normal to the a and c axes presented discontinuities, ∼2.25 Å wide, parallel to the (010) plane, with no electronic density maxima, thus suggesting that adjacent planes are joined by van der Waals-like residual links. Partial dissolution was detected on both octahedral and tetrahedral sheets, beginning by breaking the ribbons not along the edges, but in the centre, thus creating a 5.20 x 66.79 Å tunnel along the a axis. By interrupting the tetrahedral sheet, this mechanism changes the phyllosilicate-like nature of the sepiolite to an inosilicate-like structure.
Firing transformations of a carbonatic clay from the High–Atlas, Morocco
Authors: Kacim S. , Hajjaji M. 
Published: January 2004

AbstractThe firing transformations of a Triassic calcareous clay were investigated, in the range 800 –1075ºC, by using X-ray diffraction and by measuring some ceramic properties (linear shrinkage, density and porosity). It was found that gehlenite and wollastonite are the only neoformed crystalline phases, when anorthite is also expected. The occurrence of these phases is discussed, emphasizing the role of the activity of free silica and calcite concentration. Moreover, new reaction paths for anorthite and wollastonite are envisaged.
Surface microtopography of sudoite
Authors: Jige M. , Kitagawa R. , Zaykov V. V. , Sinyakovskaya I . 
Published: January 2004

AbstractThe gold-decoration technique of electron microscopy is used to study the surface microtopography of natural (001) surfaces of sudoite collected from a hydrothermal vein of the Berezovsk gold deposit, Central Urals, Russia. Only closed step patterns with malformed and/or nearly circular islands were observed on the (001) growth surface of sudoite crystals, implying a twodimensional nucleation mechanism. This is in contrast to the spiral step patterns commonly recognized on growth surfaces of other clay minerals, such as illite and kaolinite, formed under hydrothermal conditions. It is inferred that the crystallization of sudoite occurred under relatively higher temperatures and/or from more highly supersaturated fluids than many other hydrothermal clay minerals so far described.
Zeolite crystal habits, compositions, and paragenesis; Blackhead Quarry, Dunedin, New Zealand
Authors: Graham I. T. , Pogson R. E. , Colchester D. M. , Baines A. 
Published: January 2004

AbstractBlackhead Quarry exploits a small Miocene (~10 Ma) basanitic volcanic centre in the Dunedin Volcanic Group, New Zealand. Vesicles near the quarry top contain Ca– and Na-rich zeolites, abundant calcite and rare pyrite resulting from localized low-T hydrothermal alteration (<100°C). Mineral assemblages were characterized by EDS and laser Raman spectroscopy with the latter the most useful in determining the identity of fibrous zeolite species. Secondary mineral assemblages crystallized during final stages of lava cooling from aqueous solutions enriched in Ca, Na, K, Ba and (CO3)2–leached from surrounding calcareous rocks and basanite. Phillipsite-K (generation I) crystallized first (in some places directly on fresh basanite) followed by the Ca-rich zeolites, chabazite-Ca, calcian phillipsite–K (generation II), gismondine and thomsonite. Later Na-rich fluids crystallized gonnardite and natrolite, and finally calcite from late Ca-rich fluids. Zeolite composition is not reflected by morphology. For example, both phacolitic and pseudocubic chabazite are chabazite-Ca, and although all phillipsite crystals have a similar habit, their composition varies widely. Various lithologies comprising the Blackhead volcanic centre have unique secondary mineral paragenetic sequences controlled largely by the rock structure and solution chemistry.
Rhönite paragenesis in pyroxenite xenoliths, Mount Sidley volcano, Marie Byrd Land, West Antarctica
Authors: Grapes R. H. , Wysoczanski R. J. , Hoskin P. W. O. 
Published: January 2004

AbstractRhönite occurs in lower crustal pyroxenite xenoliths erupted in phonolite from the Mount Sidley composite volcano, Marie Byrd Land, Antarctica, as a localized breakdown product, with plagioclase, clinopyroxene, ± olivine ± Ti-magnetite + melt, of kaersutite, and as microphenocrysts (with olivine, plagioclase, clinopyroxene) in pockets of basanitic melt. Rhö nite after kaersutite has a more NaSi-rich/ CaAl-poor composition, lower Ti, and formed at higher oxidation (∼NNO) conditions than rhönite occurring as microphenocrysts in basanite. Comparison with experimentally determined rhönite stability in understaturated alkali basalt and as a reaction product after Ti-amphibole indicates that the Mount Sidley rhönite (and associated minerals) formed between 1090 and 1190°C at <0.5 kbar, presumably during temporary residence of the xenoliths in a shallow magma chamber below the volcanic edifice.
Kinetic parameters associated with self-heating of New Zealand coals under adiabatic conditions
Authors: Beamish B. B. , George J. D. St. , Barakat M. A. 
Published: January 2004

AbstractAdiabatic self-heating tests were carried out on five New Zealand coal samples ranging in rank from lignite to high-volatile bituminous. Kinetic parameters of oxidation were obtained from the self-heating curves assuming Arrhenius behaviour. The activation energy E (kJ mol–1) and the pre-exponential factor A (s–1) were determined in the temperature range of 70–140°C. The activation energy exhibited a definite rank relationship with a minimum E of 55 kJ mol–1 occurring at a Suggate rank of ∼6.2 corresponding to subbituminous C. Either side of this rank there was a noticeable increase in the activation energy indicating lower reactivity of the coal. A similar rank trend was also observed in the R70 self-heating rate index values that were taken from the initial portion of the self-heating curve from 40 to 70°C. From these results it is clear that the adiabatic method is capable of providing reliable kinetic parameters of coal oxidation.
Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain
Authors: Hoskin P. W. O. , Burns P. C. 
Published: January 2004

AbstractCompreignacite, a naturally occurring potassium uranyl oxide hydrate, is an expected alteration product of spent nuclear fuel subjected to oxidative corrosion in the presence of water. Ion-exchange experiments were performed using natural crystals of compreignacite in a 2 M CsCl solution at 180°C for 24 h, and in a 100 ppm CsCl solution at 90°C for 14 days. Exchange of Cs into crystals of compreignacite was demonstrated by crystal-structure analysis for a crystal from 2 M solution and chemical analysis for crystals from both exchange experiments. The structure of Cs-exchanged compreignacite is hexagonal, space group P2m, a= 14.1014 (18) Å, c = 15.127(3) Å, V = 2605.1(7) Å2. It was solved by direct methods and refined on the basis of F2 for all unique reflections to a final R1 = 6.37%. The structure determination demonstrated almost complete exchange of Cs for K in the interlayer of the structure, as confirmed by compositional analysis of the crystals, and provided the formula Cs6[(UO2)12(OH)10O10](H2O)3.5, Z= 2. The structure of Cs-exchanged compreignacite contains α-U3O8-type sheets of uranyl pentagonal bipyramids that are topologically identical, although compositionally distinct, to those in compreignacite. Compreignacite crystals placed in 100 ppm CsCl solution also incorporated substantial Cs by ion exchange. Ion exchange experiments, using Cs-exchanged compreignacite from earlier experiments, in 2 M KCl solution at 90°C for 14 days showed that compreignacite will retain significant Cs in the presence of a solution rich in K. These experiments indicate that formation of compreignacite structure-type phases in a geological repository due to alteration of nuclear waste may significantly impact upon the mobility of Cs, either by direct incorporation of Cs into growing crystals, or by exchange of Cs into earlier-formed crystals of compreignacite when they contact Cs-bearing solutions.
Hydroxylian pseudorutile derived from picroilmenite in the Murray Basin, southeastern Australia
Authors: Grey I. E. , Li C. 
Published: January 2004

AbstractIlmenite concentrates obtained from heavy mineral deposits in the Murray Basin, southeastern Australia contain appreciable quantities (up to 10 wt.%) of an unusual hydrated Fe titanate mineral in the form of orange to red coloured translucent grains. The grains are weakly magnetic and have a low apparent density (<3.3 g cm–3) due to microprosity, which enables them to be easily concentrated in a pure state. Samples from different deposits have similar analyses of 67–69% TiO2, 8 –9% Fe2O3, 2–3% FeO, 11 –12% H2O and 8 –9% of intra-pore impurities, mainly SiO2 and Al2O3. The powder pattern for the mineral closely matches that for pseudorutile; having a hexagonal subcell with a = 2.844 (1) Å, c = 4.575 (1) Å. The idealized composition range of the Fe titanate, calculated from analyses and structure refinements, is [FeTi6O12(OH)3].3H2O to [FeTi6O11(OH)5].2H2O. The molecular water is nonstructural, probably adsorbed on the surfaces of nano-scale domains of the mineral. Electron microprobe and scanning electron microscopy studies provide evidence for formation of the mineral by replacement reactions acting on MgO-rich ferrian ilmenite grains. The mineral represents a distinct intermediate in the chemical weathering of ilmenite, having a pseudorutile-like structure but a leucoxene-like composition. It is unusual in not having undergone any recrystallization to phases such as rutile and anatase.
Evolutionary stages of crystallization of weakly peralkaline syenites: evidence from ejecta in the plinian deposits of Agua de Pau volcano (São Miguel, Azores Islands)
Authors: Ridolfi F. , Renzulli A. , Santi P. , Upton B. G. J. 
Published: January 2004

AbstractWeakly peralkaline syenite ejecta within the plinian fall deposits of Agua de Pau volcano (São Miguel, Azores Islands) are divisible into (1) silica-undersaturated and (2) silica-saturated/oversaturated groups. The first group occurs in the pre-Fogo-A pyroclastic falls (15.2 ka) whereas the second occurs in the Fogo-A pumices (5 ka). The petrography indicates that the syenites of both groups crystallized at shallow depths and whole-rock geochemistry shows that they have compositions reflecting those of the Agua de Pau trachyte magmas. The syenites are inferred to be derived from solidification zones around the margins of the parental magma chamber. Mineral parageneses in both syenite groups permit distinction of three magmatic stages of crystallization: (1) an early crystallization stage; (2) a main crystallization stage during which most of the feldspar growth occurred; and (3) a late interstitial stage. Crystallization of the trachytic magmas yielded peralkaline residuals, highly enriched in volatiles, alkalis, HFSE andREE. In the silica-undersaturated syenites, the complex Zr-Ti silicate minerals, eudialyte and a låvenite-like mineral, crystallized interstitially from the residual magmas. In contrast, the zircono-silicate dalyite, andREE-rich minerals (chevkinite-(Ce), britholite-(Ce) and pyrochlore), together with thorite, were late-stage interstitial products of the silica-saturated/oversaturated syenites.
Nickelphosphide from the Vicenice octahedrite: Rietveld crystal structure refinement of a synthetic analogue
Authors: Skála R. , M. Drábek  
Published: January 2004

AbstractThe original description of nickelphosphide from the Butler meteorite [(Ni1.83Fe1.21)Σ3.04P0.96 to (Ni1.71Fe1.28Co0.01)Σ3.00P1.00] lacks detailed and accurate powder data – with only 11 observed reflections down to 1.37 Å. Consequently, no crystal structure information for this phase is available. Here we present the crystal structure for a synthetic analogue of the phase found in the Vicenice IID medium octahedrite (with a mean empirical formula of (Ni1.69Fe1.31)Σ3.00P1.00) and a hypothetical Ni3P end-member. Unit-cell dimensions of the synthetic analogue of Ni1.68Fe1.33P0.99 composition from individual peak profile fitting of XRD data collected with Cu radiation are a= 9.0168(2)Å, c= 4.4491(1)Å, V= 361.72(1)Å3 and those for Ni3P composition are a= 8.9546(1)Å, c= 4.38714(8)Å, V= 351.783(8)Å3. The space group of the mineral is I4¯ and Z= 8. The crystal structure refined from powder data by the Rietveld method is consistent with that refined and published for Fe3P and Ni3P synthetic compounds as well as Fe-dominant schreibersite from single-crystal data. However, because of the similarity of the scattering of iron and nickel, we were not able to refine directly the site occupancies in the synthetic analogue of the nickelphosphide from the Vicenice iron meteorite.
On the significance of small deviations from higher symmetry
Authors: Baur W. H. , Fischer R. X. 
Published: January 2004

AbstractSmall deviations from higher symmetry can be established by single-crystal diffraction methods by (1) measuring the metric of the unit cell with high, non-routine precision; (2) measuring a full reflection sphere of diffraction data and testing it for the presence or absence of symmetry elements in the dataset; (3) refining the structure in both the higher and the lower symmetry and comparing the results; (4) checking the refined crystal structures for the presence or absence of hidden symmetry elements. By these criteria it is not established that the v{120} growth sector of yugawaralite really has triclinic symmetry (Tanaka et al., 2002). On the contrary, the refined metrical parameters and the atomic positions conform to monoclinic symmetry within the margins of experimental error.
Textural and spectroscopic studies on hydrothermal dumortierite from an Al-rich clay deposit, southeastern Korea
Authors: Choo C. O. , Kim Y. 
Published: January 2004

AbstractDumortierite occurs as small nodules or thin layers along horizontal fractures in the altered volcanic rocks of the Milyang clay deposit, southeastern Korea. Textural evidence shows that dumortierite is associated with pyrophyllite, suggesting that the silica activity increased with decreasing B and Al activities during the hydrothermal alteration. Dumortierite chemistry shows a slight excess of Al, possibly due to common occurrence of Al-rich minerals in the clay deposit. The structural formula of dumortierite is recalculated as Al6.93(Fe0.03Mg0.07)B(Si2.99Al0.01)O18. An absorption peak at 1387 cm–1 in the IR spectrum indicates that B is present in three-fold coordinated sites. The 29Si MAS NMR spectrum has two peaks at –90.9 and –95.5 ppm, showing that Si in dumortierite is located in two different crystallographic sites and is linked to four octahedral Al atoms. The 27Al MAS NMR spectrum shows only one asymmetrical peak near 0 ppm, suggesting that there is no substitution of Al for Si. The 11B MAS NMR spectrum at 17.5 ppm shows a typical second order quadrupole pattern represented by the three-fold coordinated B. The 11B chemical shifts indicate that all of the B occupies such sites, indicating that the B sites are axially symmetric or nearly so in a very well defined site.
Geochemistry of biotite in metabentonites as an age discriminant, indicator of regional magma sources and potential correlating tool
Authors: Batchelor R. A. 
Published: January 2004

AbstractThe chemical composition of unaltered biotites extracted from 18 Lower Palaeozoic metabentonites from Sweden, Norway and Scotland was determined. Discrimination based on FeO, MgO and TiO2proved able to separate the metabentonites on the basis of their stratigraphical age. A triangular discrimination diagram using MgO, FeO and Al2O3classified the biotites as calc-alkaline. Independent support for the discriminant power of FeO, MgO and TiO2in biotite comes from Sr isotope ratios and Sr concentration data from cognate apatite crystals. Within this dataset Caradocian and Llandoverian metabentonites have unique biotite compositions, while Wenlockian samples can be characterized to a lesser degree. Biotite composition also supported the correlation of a pair of metabentonites from Norway known to form part of the same horizon. Biotite in metabentonites preserves the chemical signature of the host magmas in which it crystallized and can be used to discriminate between metabentonites of different ages and provenance.
Structural phase transitions and mixing behaviour of the Ba-aluminate (BaAl2O4)– Sr-aluminate (SrAl2O4) solid solution
Authors: Rodehorst U. , Carpenter M. A. , Marion S. , Henderson C. M. B. 
Published: January 2004

AbstractPhase transitions in the BaAl2O4–SrAl2O4solid solution have been analysed as a function of temperature and composition using infrared (IR) powder absorption spectroscopy. The improper ferroelectric phase transitionP6322 →P63(2A superstructure) in the BaAl2O4end-member can be detected through a change in slope of the wavenumbers of hard modes at ∽450 K. A change in line widths at ∽520 K appears to correlate with the development of diffuse intensity ina*-b*planes of electron diffraction patterns reported elsewhere in the literature. The same shift in wavenumber of hard modes is not observed in spectra from samples with compositions corresponding to 60, 80 and 90% of BaAl2O4component, but a change in line widths at ∽500 K has been tentatively explained in terms of a different phase transition, from aP6322 parent structure to aP63(√3A superstructure) product. Strain analysis of published high-temperature lattice parameter data suggests that the hexagonal → monoclinic transition in Sr-rich members of the solid solution may consist of two discrete transitions, and a sequenceP6322 →C2 →P21is suggested. The second transition could be related to instabilities in the hexagonal solid solution. Autocorrelation analysis of the IR spectra reveals a large positive deviation from linear behaviour across the solid solution, which is interpreted in terms of microscopic strain effects. These microscopic strains are probably responsible for the different transformation behaviour shown by samples with different compositions across the solid solution.
Fahlore as a petrogenetic indicator: Keno Hill Ag-Pb-Zn District, Yukon, Canada
Authors: Sack R. O. , Lynch J. V. G. , Foit F. 
Published: January 2004

AbstractFahlores [~(Cu,Ag)10(Zn,Fe)2Sb4S13] from the Keno Hill mining district, central Yukon, Canada record virtually the entire petrogenetic history of a Cretaceous hydrothermal system extending over 40 km outward from the Mayo Lake granitic pluton. These fahlores are an essential constituent of polymetallic sulphide veins developed in a graphitic Mississippian quartzite, where they occur in association with sphalerite, pyrargyrite, galena and siderite. Fahlores exhibit pronounced east-west zoning in average Ag/(Ag+Cu) and Zn/(Zn+Fe) values, with these simultaneously increasing and decreasing from east to west over 20 km of hydrothermal activity. These zonations are coupled with average Ag/(Ag+Cu) and Zn/(Zn+Fe) values in fahlore roughly paralleling the 300°C isotherm for fahlores in equilibrium with pyrargyrite, miargyrite and sphalerite in the simple system Ag2S-Cu2S-ZnS-FeS-Sb2S3. Early high-Ag, high-Zn fahlores from the eastern and western mines have Ag/(Ag+Cu) and Zn/(Zn+Fe) values requiring temperatures ≥400°C, in agreement with temperatures established from the As-content of arsenopyrite coexisting with pyrite, pyrrhotite and sphalerite. Ag/(Ag+Cu) and Zn/(Zn + Fe) values in later, main-stage fahlores are consistent with the 250–310°C range of temperatures established for boiling of Keno Hill fluids. Finally, Ag- and Fe-rich fahlores were produced by retrograde Fe-Zn exchange with sphalerite or crystallized from late-stage epithermal fluids which produced polybasite, stephanite, acanthite and wire silver. One such fahlore exhibits unmixing into high-Ag and low-Ag varieties. This is the first reported miscibility gap for freibergite fahlores and confirms the earlier prediction of such gaps.
Redefinition of arhbarite, Cu2Mg(AsO4)(OH)3
Authors: Krause W. , Bernhardt H.-J. , Effenberger H. , Kolitsch U. , Lengauer CH. 
Published: January 2004

AbstractArhbarite was described in 1982 as a new copper arsenate, Cu2(OH)AsO4·6H2O, from the Arhbar mine, Morocco. Due to the very small grain size no crystallographic data other than the X-ray powder diffraction data could be given. Reinvestigation of the type material and of new finds from the El Guanaco mine, Chile, is based on Rietveld refinement of X-ray powder data, electron microprobe investigations, optical studies as well as infrared and Raman spectra. The main results are: (1) arhbarite has the ideal formula Cu2Mg(AsO4)(OH)3 with magnesium oxide as an additional constituent and (2) arhbarite is isotypic with gilmarite, Cu3(AsO4)(OH)3. Arhbarite is triclinic, space group P1 (no. 1), unit-cell parameters (type material; refined from powder data) a= 5.315(4), b= 5.978(6), c= 5.030(6)Å, α = 113.58(6), β = 97.14(7), γ = 89.30(8)°, V= 145.2(1)Å3, Z= 1. Microprobe analyses of the type material gave MgO 10.20, CuO 47.46, NiO 0.20, CoO 0.24, As2O5 33.85, SiO2 0.10, H2O 7.58 (calc.), total 99.63 wt.%. The empirical formula is Cu1.98(Mg0.88Cu0.09Ni0.01Co0.01)S0.99(AsO4)1.02(OH)2.92, based on 7 O atoms. The Chilean arhbarite shows a slightly higher Cu content than the type material; it has the formula Cu1.99(Mg0.73Cu0.25Zn0.01)∑0.99[(AsO4)1.01(SiO4)0.01]∑1.02(OH)2.92. The formal redefinition of arhbarite has been approved by the CNMMN of the IMA.