bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics from first principles: temperature and composition of the Earth’s core
Authors: Alfé D. , Gillan M. J. , Price G. D. 
Published: May 2003

AbstractWe summarize the main ideas used to determine the thermodynamic properties of pure systems and binary alloys from first principles calculations. These are based on the ab initio calculations of free energies. As an application we present the study of iron and iron alloys under Earth,s core conditions. In particular, we report the whole melting curve of iron under these conditions, and we put constraints on the composition of the core. We found that iron melts at 6350士600 K at the pressure corresponding to the boundary between the solid inner core and the liquid outer core (ICB). We show that the core could not have been formed from a binary mixture of Fe with S, Si or O and we propose a ternary or quaternary mixture with 8—10% of S/Si in both liquid and solid and an additional ~8% of oxygen in the liquid. Based on this proposed composition we calculate the shift of melting temperature with respect to the melting temperature of pure Fe of ~—700 K, so that our best estimate for the temperature of the Earth's core at ICB is 5650±600 K.
Laser Raman identification of silica phases comprising microtextural components of sinters
Authors: Rodgers K. A. , Hampton W. A. 
Published: May 2003

AbstractLaser Raman spectroscopy is particularly well suited for routine characterization of the crystalline and the better ordered paracrystalline silica phases occurring in silica sinters: opal-C, quartz and moganite. The non-crystalline and poorly ordered paracrystalline silica phases (opal-CT and opal-A) are identified with difficulty, partly as a result of the high level of fluorescence exhibited by the younger sinters that are dominated by these phases, and partly as a result of the ill-defined nature of the broad phonon scattering bands produced by them. Nonetheless, given the limited number of phases present and the high level of phonon scattering from the better ordered phases, judicious use of a Raman microprobe enables the character of most siliceous microtextural sinter components to be determined readily. Microprobe examination of a series of New Zealand sinters, ranging from Late Quaternary to Pliocene in age shows that a silica phase inhomogeneity that exists in some outcrops reflects an underlying phase heterogeneity obtaining in the microstructure of the sinter; it is a consequence of the phase transformation process. In the older sinters, quartz, moganite and opaline cristobalite may be present in a single fabric element but in quite different proportions to their abundance in adjacent elements. Identification of opaline lepispheres partially pseudomorphed by quartz+moganite and the association of quartz+moganite in microcrystals exhibiting common quartz forms, cautions against the use of morphology as a means of identifying silica phases at the microstructural level.
Crystal structure refinement of sahlinite Pb14(AsO4)2O9Cl4
Authors: Bonaccorsi E. , Pasero M. 
Published: May 2003

AbstractThe crystal structure of sahlinite [Pb14(AsO4)2O9Cl4] from Lågban (Sweden) has been refined up toR= 0.071 using single-crystal diffraction data collected at the Elettra synchrotron facility. Sahlinite is monoclinic, space group C2/c, witha= 12.704(4),b= 22.576(5),c= 11.287(4) Å, β = 118.37(3)°. Sahlinite is isostructural with kombatite, its vanadium counterpart. Both are derivatives of the litharge form of PbO. In the structure of sahlinite there are seven independent Pb atoms, which are linked to Cl and/or O atoms, with coordination number ranging from V to VIII. The coordination polyhedra are irregularly shaped, due to the 6s2lone-pair effect displayed by Pb2+.
Modes and textures of secondary minerals on Chinese coins of different ages
Authors: Fang J. N. , Tan L. P. , Huang E. 
Published: May 2003

AbstractA thorough assessment of the secondary minerals on 796 Chinese Pb-Cu-Sn-Zn bronze coins from ∼1100 BC to AD 1911 has been made. Malachite is found on more than 80% of the coins irrespective of their dynasties, but a botryoidal texture is only observed on the coins of the Song dynasty or older. Azurite, however, is seen in microscopic quantities on a single coin of ∼AD 1800, but is clearly visible on the Ming dynasty or older coins. Cerussite is a common secondary mineral of the Qin dynasty and older coins, though it has not been found on the Qing dynasty or younger coins. Cuprite is observed on the Song dynasty and older coins.
Tripuhyite, FeSbO4, revisited
Authors: Berlepsch P. , Armbruster T. , Brugger J. , Criddle A. J. , Graeser S. 
Published: May 2003

AbstractThe exact nature of tripuhyite remains controversial more than 100 years after the first description of the mineral. Different stoichiometries and crystal structures (rutile or tri-rutile types) have been suggested for this Fe-Sb-oxide. To address these uncertainties, we studied tripuhyite from Tripuhy, Minas Gerais, Brazil (type material) and Falotta, Grisons, Switzerland using single-crystal and powder X-ray diffraction (XRD), optical microscopy and electron microprobe analysis.Electron microprobe analyses showed the Fe/Sb ratios to be close to one in tripuhyite from both localities. Single crystal XRD studies revealed that tripuhyite from the type locality and from Falotta have the rutile structure (P42mnm, a = 4.625(4) c = 3.059(5) and a = 4.6433(10) c= 3.0815(9) Å, respectively). Despite careful examination, no evidence for a tripled c parameter, characteristic of the tri-rutile structure, was found and hence the structure was refined with the rutile model and complete Fe-Sb disorder over the cationic sites in both cases (type material: R1 = 3.61%; Falotta material: R1 = 3.96%). The specular reflectance values of type material tripuhyite and lewisite were measured and the following refractive indices calculated (after Koenigsberger): tripuhyite nmin = 2.14, nmax = 2.27; lewisite (cubic) n = 2.04.These results, together with those of 57Fe and 121Sb Mössbauer spectroscopy on natural and synthetic tripuhyites reported in the literature, indicate that the chemical formula of tripuhyite is Fe3+Sb5+O4 (FeSbO4). Thus, tripuhyite can no longer be attributed to the tapiolite group of minerals of general type AB2O6. A comparison of the results presented with the mineralogical data of squawcreekite suggests that tripuhyite and squawcreekite are identical. In consequence, tripuhyite was redefined as Fe3+Sb5+O4 with a rutile-type structure. Both the proposed new formula and unit cell (rutile-type) of tripuhyite as well as the discreditation of squawcreekite have been approved by the Commission on New Mineral and Mineral Names (CNMMN) of the International Mineralogical Association (IMA).
A single crystal X-ray study of a sulphate-bearing buttgenbachite, Cu36Cl7.8(NO3)1.3(SO4)0.35(OH)62.2.5.2H2O, and a re-examination of the crystal chemistry of the buttgenbachite-connellite series
Authors: Hibbs D. E. , Leverett P. , Williams P. A. 
Published: May 2003

AbstractThe single-crystal X-ray structure of a sulphate-bearing buttgenbachite, Cu36Cl7.8(NO3)1.3(SO4)0.35(OH)62.2.5.2H2O, from Likasi, Democratic Republic of Congo, has been determined at 100 and 288 K. The basic framework of the structure is the same as has been previously reported for buttgenbachite, except for the identification of a hydrogen-bonded chloride ion (occupancy 0.6) at the origin instead of a Cu ion with partial occupancy. The nature of nitrate positional disorder along channels in the c direction and how this relates to the presence of other species such as chloride ions and water molecules and, most importantly, sulphate ions has been elucidated. One nitrate ion, with an occupancy of 0.18, lies at 2/3,l/3,l/4 and shares the site with a chloride ion (occupancy 0.30) and also a sulphate ion (occupancy 0.09); a second nitrate, with an occupancy of 0.24, lies at 2/3,1/3,0.084 and shares the site with a water molecule (occupancy 0.06). As a result, a formula of Cu36Cl7.8(NO3)1.3(SO4)0.35(OH)62.2.5.2H2O is obtained. Re-refinement of deposited data for a supposed connellite crystal from the Toughnut mine,Tombstone, Arizona gives a related, but different, pattern of anion substitution. No sulphate could be detected in the structure and it is evident that this structure refers to buttgenbachite. A nitrate nitrogen atom and a chloride ion are disordered at 2/3,l/3,l/4, the overall site being fully occupied. A chloride ion with ∼0.5 occupancy is sited at the origin and the formula Cu36Cl7.9(NO3)1.1(OH)63.4H2O is indicated. Re-refinement of a deposited data set for another buttgenbachite crystal from the Likasi mine reveals a partially occupied nitrate centred at 2/3,l/3, z and a partially occupied chloride at 2/3,l/3,l/4. Either 0.5Cl–, OH–, H2O or H3O+ is located at the origin. If the latter is the case, the stoichiometry for this buttgenbachite is Cu36Cl6.5(NO3)1.5(OH)64.5.5H2O. The present study has highlighted the fact that a range of compositions for buttgenbachite exists, depending on the pH and relative activities of chloride, nitrate and sulphate ions in solutions from which the mineral crystallizes.
HighP-Texperimental metasomatism of a fluorapatite with significant britholite and fluorellestadite components: implications forLREEmobility during granulite-facies metamorphism
Authors: Harlov D. E. , Förster H.-J. , Schmidt C. 
Published: May 2003

AbstractALREE-, Si-, S-enriched fluorapatite with ∼7.7 wt.%LREE2O3, 5.3 wt.% SiO2and 3.5 wt.% SO3from the Mushugai-KhudukREEdeposit, southern Mongolia, has been experimentally metasomatized in pure H2O at 900°C and 1000 MPa. Despite the highLREEcontent, inclusions or rim grains of monazite did not form during fluid-induced metasomatism. Under high-contrast BSE imaging, the reacted fluorapatite presents a mottled appearance with light, moderate and dark areas and hosts large fluid inclusions containing anhydrite as the solid phase. Dark areas show moderate depletion in all theLREE.MeasurableHREEsuch as Gd and Y remain unchanged. In the areas of intermediate brightness, Ce and, to a lesser extent, La are moderately enriched relative to the original fluorapatite. In the light areas, Ce and La display strong enrichment, whereas the otherLREE,Gd and Y remain little changed. In the dark areas, depletion inLREEis matched by depletion in Si and Na, satisfying the coupled substitution reactions Si4+; + (LREE)3+= P5++ Ca2+and Na++ (LREE)3+= 2Ca2+. In the light areas, enrichment inLREEand P is accompanied by depletion in Si, Na and S, implying operation of two different coupled substitution reactions, namely: 2P5+= Si4++ S6+and 2P5++ LREE3+= 2S6++ Na+. In all areas, strong enrichment in F is accompanied by strong depletion in Cl and OH. The formation of large, fluid and anhydrite-filled inclusions associated with theLREE-enriched light areas is evidence of a negative volume change, combined with additional local dissolution of the fluorapatite. This occurred during the metasomatism of the original Cl- and OH-bearing fluorapatite to a nearly pure end-member fluorapatite. Local dissolution of fluorapatite in the space now occupied by the voids, combined with element remobilization from the body of the fluorapatite as a whole, provided the Ca and S needed for the formation of anhydrite as well as the P andLREErequired for the enrichment of the bright areas.
Space symmetry of prehnite，Ca2AI[6](Si3AIO10)(OH)2, from the Tieshan iron mineral deposit, Central China
Authors: Zhao W.-y. , Liu X.-w. , Wang Q.-y. , Zhang Q.-j. 
Published: May 2003

AbstractThe space symmetry of prehnite, a mineral which occurs in cavities and veins within skarn from the Tieshan iron mineral deposit, Daye, Hubei province, central China, has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale. Our results confirm that natural prehnite may belong to space group Pncm. The unit-cell parameters of the prehnite investigated ( a = 0.458 nm, b = 0.555 nm and c = 1.853 nm) have been calculated using the multicrystal diffraction rings of gold, the internal standard.
Paragenesis and mineral chemistry of alabandite (MnS) from the Ag-rich Santo Toribio epithermal deposit, Northern Peru
Authors: Olivo G. R. , Gibbs K. 
Published: May 2003

AbstractThe Miocene, epithermal, Ag-rich polymetallic Santo Toribio deposit is hosted by the volcanics of the Quiruvilva-Pierina subbelt, Northern Peru, which also comprises the world-class, high sulphidation Pierina deposit. The Ag-rich, alabandite-bearing veins of the Santo Toribio deposit formed during two major stages. The early stage is characterized by deposition of arsenopyrite, pyrite, quartz, Mn- sphalerite, stannite, alabandite and minor miargyrite. Sphalerite associated with this stage is exceptionally enriched in Mn (up to 14.5 wt.%) and alabandite is optically and mineralogically zoned. Its brown zones have greater Fe+Sb and smaller Mn contents than the green zones and Fe+Sb replaces Mn in its structure. During this early stage, fs2 must have been high to allow the stabilization of alabandite relative to rhodochrosite. In the second stage, the physicochemical conditions changed and the CO2/S ratio increased, causing dissolution of alabandite and the deposition of abundant rhodochrosite and a second generation of arsenopyrite, pyrite and quartz, sphalerite with chalcopyrite inclusions, mirargyrite, ramdohrite, and finally stibnite. This polymetallic ore probably formed due to an abrupt decrease in H+ and/or Cl- concentration caused by boiling or dilution of the high-salinity hydrothermal fluids and constitutes an example of “intermediate sulfidation-state” epithermal deposits.
Raman spectroscopy of the minerals boléite，cumengéite， diaboléte and phosgenite — implications for the analysis of cosmetics of antiquity
Authors: Frost R. L. , Williams P. A. , Martens W. 
Published: May 2003

AbstractThe application of Raman spectroscopy to the study of the mixed cationic Pb-Cu and Pb-Cu-Ag minerals: boleite, cumengeite and diaboleite has enabled their molecular structures to be compared. Each of these three minerals shows different hydroxyl-stretching vibrational patterns, but some similarity exists in the Raman spectra of the hydroxyl-deformation modes. The low-wavenumber region is characterized by the bands assigned to the cation-chloride stretching and bending modes. Phosgenite is also a mixed chloride-carbonate mineral and a comparison is made with the molecular structure of the aforementioned minerals. Raman spectroscopy lends itself to the study of these types of minerals in complex mineral systems of secondary mineral formation.
The crystal structure of anthropogenic Pb2(OH)3(NO3), and a review of Pb-(O,OH) clusters and lead nitrates
Authors: Kolitsch U. , Tillmanns E. 
Published: May 2003

AbstractThe previously unknown crystal structure of the basic lead nitrate Pb2(OH)3(NO3) has been determined using single-crystal X-ray diffraction data (Mo-Kα radiation, CCD area detector). The compound is orthorhombic, space groupImmm,witha= 8.314(2),b= 8.545(2),c= 17.210(3)Å(R1 = 2.78% for 940 ‘observed’ reflections with Fo > 4σ(Fo)). The layered structure contains a previously unknown cuboid [Pb8(OH)12]4+cluster and NO3groups. The study used crystals formed by anthropogenic processes on a medieval mine dump, probably involving black gunpowder used in the blasting of ore. Pb2(OH)3(NO3) is associated with a second nitrate, Pb13O8(OH)6(NO3)4, which was previously designated as “Pb3O3(OH)4(NO3)2” or “Pb3(OH)5(NO3)”. It is rhombohedral, space group, witha= 10.263(1),c= 25.454(5) Å, and a structure solution is in complete agreement with an independent single-crystal study by Liet al.(2001). Probable hydrogen bonds in Pb2(OH)3(NO3) are indicated. Reported data onclusters and lead hydroxide and oxide nitrates are summarized and discussed critically. The probable conditions of formation of the studied samples are evaluated.
Processing, inversion, and interpretation of a 2D seismic data set from the North Viking Graben, North Sea
Authors: Madiba Gislain B. , McMechan George A. 
Published: May 2003

Simultaneous elastic impedance inversion is performed on the 2D North Viking Graben seismic data set used at the 1994 SEG workshop on amplitude variation with offset and inversion. P‐velocity (Vp), S‐velocity (Vs), density logs, and seismic data are input to the inversion. The inverted P‐impedance and S‐impedance sections are used to generate an approximate compressional‐to‐shear velocity ratio (Vp/Vs) section which, in turn, is used along with water‐filled porosity (Swv) derived from the logs from two wells, to generate fluid estimate sections. This is possible as the reservoir sands have fairly constant total porosity of approximately 28 ± 4%, so the hydrocarbon filled porosity is the total porosity minus the water‐filled porosity.To enhance the separation of lithologies and of fluid content, we map Vp/Vsinto Swvusing an empirical crossplot‐derived relation. This mapping expands the dynamic range of the low end of the Vp/Vsvalues. The different lithologies and fluids are generally well separated in the Vp/Vs–Swvdomain.Potential hydrocarbon reservoirs (as calibrated by the well data) are identified throughout the seismic section and are consistent with the fluid content estimations obtained from alternative computations.The Vp/Vs–Swvplane still does not produce unique interpretation in many situations. However, the critical distinction, which is between hydrocarbon‐bearing sands and all other geologic/reservoir configurations, is defined. Swv≤ 0.17 and Vp/Vs≤ 1.8 are the criteria that delineate potential reservoirs in this area, with decreasing Swvindicating a higher gas/oil ratio, and decreasing Vp/Vsindicating a higher sand/shale ratio. As these criteria are locally calibrated, they appear to be valid locally; they should not be applied to other data sets, which may exhibit significantly different relationships. However, the overall procedure should be generally applicable.
Merging airborne magnetic surveys into continental‐scale compilations
Authors: Minty Brian R. S. , Milligan Peter R. , Luyendyk Tony , Mackey Timothy 
Published: May 2003

Regional compilations of airborne magnetic data are becoming more common as national databases grow. Grids of the magnetic survey data are joined together to form geological province‐scale or even continental‐scale compilations. The advantage of these compilations is that large tectonic features and geological provinces can be better mapped and interpreted. We take a holistic approach to the joining of survey grids. The leveling of the grids into a regional compilation is treated as a single inverse problem. We use the weighted least‐squares method to find the best adjustment for each survey grid such that the data value differences in the grid overlap areas are minimized. The method spreads any inconsistencies between grids among all of the grid overlap areas and minimizes the introduction of long‐wavelength errors into the composite grid. This is an improvement on the conventional approach of joining grids sequentially. A comparison of leveled data over Western Australia with diurnally‐corrected long aeromagnetic traverses shows long‐wavelength errors of about 200 nT over distances of more than 5000 km. This is an improvement on the sequential grid‐joining method, which gives errors of about 450 nT over the same distance. The application of the method to a smaller area covered by good quality surveys resulted in long‐wavelength errors of about 30 nT over a distance of 1200 km. This is within the estimated accuracy of the original survey measurements. The new method is also fast—what used to take many weeks of effort can now be achieved in a matter of hours.
Inversion of multicomponent, multiazimuth, walkaway VSP data for the stiffness tensor
Authors: Dewangan Pawan , Grechka Vladimir 
Published: May 2003

Vertical seismic profiling (VSP), an established technique, can be used for estimating in‐situ anisotropy that might provide valuable information for characterization of reservoir lithology, fractures, and fluids. The P‐wave slowness components, conventionally measured in multiazimuth, walkaway VSP surveys, allow one to reconstruct some portion of the corresponding slowness surface. A major limitation of this technique is that the P‐wave slowness surface alone does not constrain a number of stiffness coefficients that may be crucial for inferring certain rock properties. Those stiffnesses can be obtained only by combining the measurements of P‐waves with those of S (or PS) modes.Here, we extend the idea of Horne and Leaney, who proved the feasibility of joint inversion of the slowness and polarization vectors of P‐ and SV‐waves for parameters of transversely isotropic media with a vertical symmetry axis (VTI symmetry). We show that there is no need to assume a priori VTI symmetry or any other specific type of anisotropy. Given a sufficient polar and azimuthal coverage of the data, the polarizations and slownesses of P and two split shear (S1 and S2) waves are sufficient for estimating all 21 elastic stiffness coefficients cijthat characterize the most general triclinic anisotropy. The inverted stiffnesses themselves indicate whether or not the data can be described by a higher‐symmetry model.We discuss three different scenarios of inverting noise‐contaminated data. First, we assume that the layers are horizontal and laterally homogeneous so that the horizontal slownesses measured at the surface are preserved at the receiver locations. This leads to a linear inversion scheme for the elastic stiffness tensor c. Second, if the S‐wave horizontal slowness at the receiver location is unknown, the elastic tensor c can be estimated in a nonlinear fashion simultaneously with obtaining the horizontal slowness components of S‐waves. The third scenario includes the nonlinear inversion for c using only the vertical slowness components and the polarization vectors of P‐ and S‐waves. We find the inversion to be stable and robust for the first and second scenarios. In contrast, errors in the estimated stiffnesses increase substantially when the horizontal slowness components of both P‐ and S‐waves are unknown. We apply our methodology to a multiazimuth, multicomponent VSP data set acquired in Vacuum field, New Mexico, and show that the medium at the receiver level can be approximated by an azimuthally rotated orthorhombic model.
Parsimonious 2D prestack Kirchhoff depth migration
Authors: Hua Biaolong , McMechan George A. 
Published: May 2003

The efficiency of prestack Kirchhoff depth migration is much improved by using ray parameter information measured from prestack common‐source and common‐receiver gathers. Ray tracing is performed only back along the emitted and emergent wave directions, and so is much reduced. The position of the intersection of the source and receiver rays is adjusted to satisfy the image time condition. The imaged amplitudes are spread along the local reflector surface only within the first Fresnel zone. There is no need to build traveltime tables before migration because the traveltime calculation is embedded into the migration. To further reduce the computation time, the input data are decimated by applying an amplitude threshold before the estimation of ray parameters, and only peak and trough points on each trace are searched for ray parameters.Numerical results show that the proposed implementation is typically 50–80 times faster than traditional Kirchhoff migration for synthetic 2D prestack data. The migration speed improvement is obtained at the expense of some reduction in migration quality; the optimal compromise is implemented by the choice of migration parameters. The main uses of the algorithm will be to get a fast first look at the main structural features and for iterative migration velocity analysis.