bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lowering of symmetry in pyribole structures
Authors: Chisholm J. E. 
Published: December 2006

AbstractThe low-symmetry forms of the clinopyroxene structure fit the rules proposed previously (Chisholm, 1981) but the low-symmetry forms of ortho- and proto-pyroxene do not. The rule governing the packing of the tetrahedral chains into layers is therefore revised to take into account the different chain configurations. Starting with simple sequences of. and × chains (Thompson, Hallimond Lecture 1979, unpubl.) a scheme is proposed for deriving most of the known pyribole structure types and their space groups.
Upper-mantle amphiboles: a review
Authors: Dawson J. B. , Smith J. V. 
Published: December 2006

AbstractTextural and chemical data are reviewed for amphiboles occurring in Cr-diopside series and Al-augite series xenoliths; as megacrysts in a variety of igneous environments; and also as minor phases in tectonic slices of upper-mantle peridotite. New data are given for pargasite and associated phases in a lherzolite from Tanzania and in kelyphite replacing garnet in a S. African kimberlite xenolith. It is concluded that only pargasites and titaniferous pargasites occurring in Cr-diopside series blocks have formed under upper-mantle conditions. Although amphibole is present in the upper mantle, as suggested by Oxburgh (1964), its relative paucity suggests it is not a major alkali and water storage site; phlogopite is a more likely candidate, particularly in the deeper parts of the upper mantle.
Chemistry and microstructure of orthoamphiboles from cordierite-amphibole rocks at Outokumpu, North Karelia, Finland
Authors: Treloar Peter J. , Putnis Andrew 
Published: December 2006

AbstractOrthoamphiboles from the cordierite-amphibole-bearing rocks at Outokumpu span a large part of the gedrite-anthophyllite solid-solution series. The amphiboles grew at temperatures near to or just above that of the solvus crest with post-metamorphic cooling resulting in sub-solvus exsolution, the distribution of which is compatible with an asymmetric solvus in which the anthophyllite limb is the steeper. Metamorphic conditions in the area imply that the crest of the solvus is unlikely to be at a temperature in excess of about 600 °C Electron microprobe traverses and Al-Kα scans show that the amphibole compositions vary rapidly both along and across grains. These variations can be explained by varying availability of Na controlling the extent of the edenitic substitution in the solid solution series. In this case this variability in Na availability may be explained by the external control of μNa through the fluid phase.
Paragonite paragenesis from the garnet granulites of the Jijal complex, Kohistan, N. Pakistan
Authors: Jan M. Q. , Wilson R. N. , Windley B. F. 
Published: December 2006

AbstractChemistry of six white micas from the high-pressure garnet granulites of Jijal is presented, together with trace elements, refractive indices, and 2Vα for one. The micas are rich in the paragonite component (over 93%), with one analysis having the highest 100 Na/(Na + K) ratio (98.5) so far reported. The paragonite is not a stable mineral of the granulites but was overprinted on the granulites at about 505–540°C and 8–9 kbar (suggesting a depth of 30 km).
The heat treatment of some Norwegian aventurinized feldspars
Authors: Copley P. A. , Gay P. 
Published: December 2006

AbstractThe morphology and structures of intergrowth precipitates in some Norwegian aventurinized plagioclases have been described in previous publications; data collected during an investigation of a wide variety of heat treatments upon the same specimens are now reported. In detail the behaviour of different feldspar crystals is highly individualistic, though there is a common pattern in sub-solidus reaction(s) with the feldspar; even if the identification of the products is uncertain, it is this process which causes the apparent ‘homogenization’ of the feldspar.Some comparisons can be made between the present studies and the more limited experiments of earlier workers, and suggestions for reconciling experimental data are discussed. On the paragenesis of aventurinized feldspars, these heating experiments confirm that mechanism(s) are complex, but that exsolution from an originally iron-enriched feldspar by cooling in the solid state is unlikely to be of more than peripheral importance.
An occurrence of the spinel end-member Mg2TiO4 and related spinel solid solutions
Authors: Gittins J. , Fawcett J. J. , Rucklidge J. C. , Brooks C. K. 
Published: December 2006

AbstractBlack, opaque grains of a spinel whose composition is (Mg2TiO4) 85.8, (MgFe2O4) 0.4 (FeFe2O4) 13.8 (mole %) coexist with a MgAl2O4 spinel and geikielite in a periclase-forsterite marble that has been thermally metamorphosed against an alkalic ultramafic intrusion of Caledonian age in the Kangerdlugssuaq region of East Greenland. The spinel appears to be the closest recorded approach to the end-member Mg2TiO4 among natural rocks, and to be part of a solid-solution series extending across the join Mg2TiO4-MgFe2O4-FeFe2O4, the existence of which has not previously been reported. The composition of the series appears to be controlled by the fO2 that prevails during metamorphism.
Porphyritic-nodular, nodular, and orbicular chrome ores from the Sakhakot-Qila complex Pakistan, and their chemical variations
Authors: Ahmed Zulfiqar 
Published: December 2006

AbstractA new kind of chromitite texture—a porphyritic nodular texture, found in an alpine-type complex in Pakistan, is described. The chromite from phenocrystic nodules and that from their disseminated chromitite groundmass show comparable trivalent elements and postcumulus to subsolidus Mg−Fe2+variations, which are also recorded from ‘normal’ nodular ore samples. The nodular ores differ from all other textural types of chromitite from this complex in an unusual, though slight, increase in Cr/(Cr+Al) with Mg/(Mg+Fe2+) between stratigraphically different desposits, which is caused by magmatic differences. The implications of major element variations in chromites and olivines of nodular chromirites are discussed and a cumulus origin is supported. Temperatures of final chromite-olivine equilibration ranged from 750 to 900 °C the individual nominal values being higher for chromitite with coarser chromite crystals and, or, higher chromite:silicate ratio.
Pyroxene fractionation in ferrobasalts from the Galapagos Spreading Centre
Authors: Muir I. D. , Mattey D. A. 
Published: December 2006

AbstractThe significance of metastable and equilibrium pyroxene fractionation trends in tholeiitic magmas is discussed, and the development of sector zoning and skeletal growth are considered in relation to Nakamura's (1973) hypothesis of protosites on growing clinopyroxene crystal surfaces. At the Galapagos Spreading Centre (GSC) basalts and ferrobasalts investigated behave paradoxically in that the slower-cooled basalts follow the quench trend while the faster-cooled ferrobasalts define a much closer approach to the equilibrium trend.It is concluded that under metastable conditions fractionation trends in Ca-rich pyroxenes may be strongly influenced by textural features such as cotectic crystallization of plagioclase and the onset of liquid immiscibility, the latter leading to the development of strongly Fe-enriched ferroaugites. Even under plutonic conditions metastable crystallization can develop and severely reduce the pyroxene miscibility gap. A model for metastable crystallization is presented. These considerations are then addressed to the remarkable correspondence of the Skaergaard and Thingmuli pyroxene fractionation trends.
Petrology of Tertiary lavas from the western Kangerdlugssuaq area, East Greenland
Authors: Fawcett J. J. , Gittins J. , Rucklidge J. C. , Brooks C. K. 
Published: December 2006

AbstractWhole-rock, minor element, rare earth, and electron microprobe data are presented for basaltic lavas from the western Kangerdlugssuaq area of East Greenland. Samples were obtained from Professor W. A. Deer's 1936 collection at Triangular Nunataks and Gardiner Plateau, and additional material obtained by sampling moraines on the surface of Kangerdlugssuaq Glacier. Both undersaturated and tholeiitic lavas are present at the Triangular Nunatak locality but the glacier suite is dominantly tholeiitic. The tholeiitic suite is less evolved than tholeiites from the Scoresby Sund area. Undersaturated lavas show enrichment in light rare earth elements and tholeiitic lavas show fiat chondrite-normalized patterns. Tholeiites from the Gardiner Plateau show no Eu anomaly but others show a slight negative Eu anomaly. Chemical data and considerations of regional geology are consistent with Cox's (1980) model of flood basalt vulcanism.
Autometasomatic alteration of gabbro, Kap Edvard Holm intrusive complex, East Greenland
Authors: Elsdon R. 
Published: December 2006

AbstractA local area of the Kap Edvard Holm Upper Layered Series gabbro has been converted into a quartz-albite-epidote ilmenite rock by leaching of iron and with a net mass loss. Among the textural changes is the dissolution of the magnetite matrix of magnetite-ilmenite lamellar intergrowths. This is an extreme example of a series of low-temperature changes occurring throughout the intrusion due to the reaction of the gabbro with a volatile-rich phase which separated during the magmatic stage and remained trapped within the walls of the intrusion. The Fe-rich fluid formed by this autometasomatic process is similar to those responsible for the genesis of Cornwall-type magnetite deposits. The probable temperature range for the process is 400–550°C.
Cryptic variation in the Kapalagulu layered intrusion, western Tanzania
Authors: Wadsworth W. J. , Dunham A. C. , Almohandis A. A. 
Published: December 2006

AbstractThe Kapalagulu intrusion displays the following sequence of cumulus phase layering in a stratigraphic sequence of 1400 m: Basal Zone (BZ) olivine ± chromite → Intermediate Zone (IZ) olivine + plag + opx →, olivine + plag + opx + cpx → Main Zone (MZ) plag + opx + cpx → plag + cpx + Fe/Ti oxide + apatite. The corresponding cryptic variation is olivine Fo83 − 77 (limited to BZ and IZ), orthopyroxene En82 − 56, clinopyroxene Ca46Mg45Fe9 to Ca43Mg37Fe21 and plagioclase An88 − 80. Reversals of the cryptic variation occur at the base of MZ (minor reversal) and in the middle of MZ (major reversal), and are attributed to the influx of relatively primitive magma. The major reversal indicates that progressive mixing of fresh and residual magmas occurred. Because of the major reversal, inverted pigeonite appears twice in the layered sequence, but at different compositions (En65 and En56). Unlike the cumulus olivine and pyroxene, cumulus plagioclase exhibits a wide range of composition (5−10% An) in individual rocks and even in single crystals.
The partial molar volume of Fe2O3 in multicomponent silicate liquids and the pressure dependence of oxygen fugacity in magmas
Authors: Mo X. , Carmichael I. S. E. , Rivers M. , Stebbins J. 
Published: December 2006

AbstractDensity measurements of eight silicate liquids containing substantial amounts of Fe2O3 have been made over a range of 250 °C. These have been combined with published density measurements on multicomponent silicate liquids to yield (by multiple regression) partial molar volumes of SiO2, TiO2, Al2O3, Fe2O3, FeO, MgO, CaO, Na2O, and K2O. The data on Fe2O3-liquids are neither precise nor abundant enough to show a compositional dependence of . In a liquid of constant composition and temperature, the pressure dependence of the oxygen fugacity is given by which, if ΔV is independent of pressure, necessitates an increase in fO2 with increasing pressure of about 1 log10 unit for 10 kbars.Combining an equation relating oxygen fugacity to composition, T, and Fe2O3 at 1 bar (Sack et al., 1980) with the results for partial molar volumes, the oxygen fugacity of any magma can be calculated as a function of P and T. If basic magmas have their Fe2O3/FeO set in the source regions, and ascend isochemically, then the calculated oxygen fugacities in the mantle increase as pressure increases and silica activity decreases. A P-T grid has been constructed to show the calculated oxygen fugacities in a source region which has equilibrated with some common lava types, based on their FeO and Fe2O3 contents.
The Pendennis peralkaline minette
Authors: Hall A. 
Published: December 2006

AbstractThe Pendennis minette has an exceptionally high K2O/Na2O ratio and is strongly peralkaline. Its constituent minerals, which are described in detail, are sanidine, biotite, two carbonates (dolomite and ferroan magnesite), two amphiboles (riebeckite and a new variety, potassium magnesio-arfvedsonite), and quartz. The major and trace dement composition of the minette indicates close affinities with the lamproitic lavas.
On the new mineral theophrastite, a nickel hydroxide, from Unst, Shetland, Scotland
Authors: Livingstone A. , Bish D. L. 
Published: December 2006

AbstractThe new mineral theophrastite, Ni(OH)2, from Unst, is Mg-bearing and occurs associated with a very poorly crystalline Ni-containing mixed hydroxide of the pyroaurite type and/or zaratite on chromitite. X-ray powder diffraction data show a shift in d spacing toward brucite compared with pure Ni(OH)2. Infrared, thermal, chemical, optical, and physical data are presented together with indexed powder data for fifteen lines ranging from d 4.66Å to 0.90Å. The solid-solution series brucite-theophrastite is briefly discussed.
A reconnaissance of trace elements in anorthoclase megacrysts
Authors: Mason R. A. , Smith J. V. , Dawson J. B. , Treves S. B. 
Published: December 2006

AbstractMajor, minor, and trace elements were measured with electron and ion microprobes for eighteen anorthoclase megacrysts from five locations. Comparisons with concentration ranges tabulated by Smith (1974) show excellent agreement except for consistently lower values of Mg and B. The discrepancy for Mg probably reflects Mg-rich impurities contaminating samples analysed by bulk methods. The cause of the discrepancy for B is unknown and deserves further study. Samples from Mt. Erebus, Antarctica, contain glass inclusions from which the following crystal/liquid partition coefficients ensue: Mg, 0.008; P, 0.04; Ti, 0.08; Fe, 0.04; Ba, 5.2; Sr, 8; Rb, 0.27.
The petrography and geochemistry of corona-bearing dolerites from the Jotun Nappe, central southern Norway
Authors: Emmett T. F. 
Published: December 2006

AbstractThe petrography and geochemistry of a suite of dolerite dykes emplaced into orthogneisses of the Jotun Nappe, central southern Norway, are described. The dolerites, which appear to be tholeiitic in character, show well-developed ophitic and doleritic textures and are not foliated. They contain corona structures of six types which represent the various stages of reaction between olivine or clinopyroxene and plagioclase, and oxide grains and plagioclase. Corona growth always proceeds after the plagioclase has become clouded with numerous extremely fine opaque particles, and reaches its fullest development in rocks with the most heavily clouded plagioclase. Garnet grows in coronas only in rocks with Fe2O3/(Fe2O3 + FeO) = 0.20 to 0.27. The ratio MgO/MgO + Fe2O3 + FeO) is of lesser importance in controlling the growth of this mineral. The role of water in coronaforming reactions, and the preservation of original igneous textures indicates that the coronas are a product of post-solidification deuterism, possibly active at high pressures and temperatures, rather than of prograde metamorphism.
Namuwite, (Zn,Cu)4SO4(OH)6.4H2O, a new mineral from Wales
Authors: Bevins Richard E. , Turgoose Stephen , Williams Peter A. 
Published: December 2006

AbstractFound on a specimen in the mineral collection of the National Museum of Wales, no. NMW 27.111.GR414, from the Aberllyn mine, Llanrwst mining field, North Wales, with hydrozincite on a breccia cemented by sphalerite, quartz, calcite, and ankerite. Atomic absorption and TGA analyses gave ZnO 37.8, CuO 22.0, SO314.9, H2O 24.5, total 99.2%, corresponding to (Zn2.50Cu1.49)Σ3.99S1.00O7·7.32 H2O on the basis of total O = 7 in the anhydrous part. The ideal formula is (Zn,Cu)4SO4(OH)6·4H2O where Zn > Cu. It is hexagonala8.29,c10.50 ± 0.01 Å, possible space groupsP6,P,P6/m,P622,P6mm,Pm2,P2m, andP6/mmm. Isomorphous with synthetic Zn,SO4(OH)66·4H2O and (Zn,Cu)4SO4(OH)6·4H2O. Strongest X-ray powder diffractions are: 10.59(100)0001, 5.31(15)0002, 4.15(25)110, 2.71(42)210, 2.63(41)211,0004, 2.41(22)212, 1.57(23)322, 1.55(20)411. Namuwite is pale sea-green in colour, lustre pearly, streak very pale green,H(Mohs) 2. Cleavage {0001}, perfect. Density (g/cm3) 2.77 (meas.), 2.81 (calc. on the normalized empirical formula). It is optically uniaxial, sign not determined owing to the extremely low birefringence. Refractive indexn= 1.577(5)(NaD). The mineral and name have been approved by the Commission on New Minerals and Mineral Names, IMA.
Evidence from feldspar compositions of high temperatures in granite sheets in the Scourian complex, N.W. Scotland
Authors: Rollinson Hugh R. 
Published: December 2006

AbstractMesoperthite feldspars from hypersolvus granites, with granulite-facies mineralogy from the Scourian complex, N.W. Scotland have an average bulk composition of (Ab0.58Or0.42)88An12. The mesoperthites have an Ab/Or ratio close to the critical composition of the alkali feldspar solvus for anorthite-free compositions. The critical temperature of the ternary feldspar solvus is estimated at high anorthite contents and used to indicate a temperature in excess of 1000°C for the crystallization of the granite sheets prior to granulite-facies metamorphism and permits a maximum water content in the melt of 1%.
Iron oxide mineralogy of a hydrothermal assemblage on Santorini Island, Aegean Sea
Authors: Murad Enver 
Published: December 2006

AbstractBasement rocks of Santorini have been locally impregnated by iron oxides and other minerals. The hydrothermal fluids which caused the mineralization have extensively altered the impregnated rocks, but left granditic garnets in these unaffected.Mössbauer spectroscopy and differential X-ray diffraction show that the iron oxides present are goethite and hematite in a ratio of about 2 : 1. The presence of hematite indicates that these minerals formed, directly from a hydrothermal phase, at higher temperatures than the recent submarine iron oxide deposits of Santorini, which contain no hematite.
The mineralogy and geochemistry of uranium, thorium, and rare-earth elements in two radioactive granites of the Vosges, France
Authors: Pagel Maurice 
Published: December 2006

AbstractTwo contrasting types of Hercynian U-rich granites can be distinguished by their accessory minerals: (1) subalkaline potassic granites (amphibole-biotite±pyroxene) characterized by apatite-zircon-thorite-sphene-allanite and rare ThO2-rich uraninite, in order of appearance in the magma, and (2) leucocratic granites (biotite and muscovite) which contain monazite-zircon-apatite-xenotime-ThO2-poor uraninite and Ti oxides. Intermediate accessory mineral associations may also exist.The mineralogy, crystallization history, and geochemistry of two high K-U-Th granites from the Vosges, France, is described. Their assemblage of U- and Th-bearing accessory minerals is listed, in order of appearance in the magma, in Group 1 (above). Trace elements (U, Th, Zr, Hf) and preliminary data on REE are discussed. In a layered sequence of the Crêtes granite, thorite, with up to 15% UO2, is shown to be important during differentiation. There is a decrease of the Th/U ratio corresponding to a slight decrease of the Th content whereas there is an increase of the U content at the end of differentiation. The Crêtes and Ballons granites have REE patterns characterized by LREE enrichment with a La/Yb ratio of about 28 (Crêtes granite) and a slight negative Eu anomaly. These relationships are typical of subalkaline potassic granites of the Hercynian. The trace element associations are similar to those of the shoshonite association with high U, Th, LREE and Ba, Rb, and Sr contents. A hypothetical model for uranium mineralization associated with such granites is discussed in the light of these data.
Uranium occurrences in the Cree Lake Zone, Saskatchewan, Canada
Authors: Parslow G. R. , Thomas D. J. 
Published: December 2006

AbstractOver 100 samples of ‘pegmatite’ and associated host rocks from the Cree Lake Zone of northern Saskatchewan have been studied. The degree of U and Th enrichment of the pegmatites appears to depend on the parent material of the anatectic melts produced during the Hudsonian thermotectonic event. Evidence for Archaean granulite-facies depletion of U and Th is inconclusive; however, important enrichment of U and Th in the basal Aphebian is associated with metamorphosed black shales and possibly evaporates.
Determination of uranium: carbon ratios in fluid inclusion decrepitates by inductively coupled plasma emission spectroscopy
Authors: Rankin A. H. , Alderton D. H. M. , Thompson M. , Goulter J. E. 
Published: December 2006

AbstractUranium has been detected in fluid inclusion decrepitates from quartz of several granites of the British Isles and from vein quartz associated with the Hcrcynian granites of SW England using ICP. Material, ejected from the inclusions during decrepitation on heating the sample, is transferred into the plasma for qualitative analysis via a stream of argon. Several other elements have been detected in the decrepitate, of which carbon is of particular interest. It shows a strong positive correlation with U and indicates the importance of C (presumably as carbonate complexes) in the transport of U in hydrothermal systems. Approximate order of magnitude estimates of the average U contents of fluid inclusions from the SW England samples, based on the assumption that U in the decrepitates is principally derived from the fluid inclusions, range from less than one to over a thousand ppm. Fluid inclusions may therefore be important in contributing to the levels of U reported in quartz (0.1 to 10 ppm).
The occurrence of uranium in association with cassiterite, wolframite, and sulphide mineralization in South-West England
Authors: Swart P. K. , Moore F. 
Published: December 2006

AbstractThe U content of cassiterite (SnO2), wolframite (Fe,Mn)WO4, and various sulphides from two localities in the Cornubian batholiths of south-west England has been investigated. Cassiterites showed concentrations of U between 0 and 6 ppm with the higher concentrations corresponding to the darker colour bands. Sulphides contained no detectable U using the fissiontrack method, but high concentrations relate to micro-veining. This veining was also evident in associated wolframite and appeared to have a composition similar to an iron-arsenate mineral associated with the alteration of arsenopyrite. Wolframite exhibited a wide range of U concentrations with sharp zonation and several generations of ore deposition within one crystal. The U was not, however, associated with either the iron- or manganese-rich phases.
Uranium-rich granites in the Olden Window, Sweden
Authors: Troëng Björn 
Published: December 2006

AbstractU-enriched granites occur in a Precambrian window in the Caledonides of central Sweden and intrude an extensive supracrustal formation dominated by acid terrestrial volcanics. During the Caledonian orogeny, thrusting, foliation, mylonites, and mesoscopic folds developed in the Precambrian rocks under low-grade metamorphic conditions. Ground and airborne γ-spectrometry indicate U-enrichment mainly in the northern part of the window where two uraniferous granites have been intruded. Several small U vein-type mineralizations are associated with one of the granites. The largest occurrence of the mineralization might be economic, and a Rb-Sr age determination has established a minimum age of 1500 Ma on the associated granite which is highly evolved.