bluuebunny/crossref_metadata_2025_split huggingface dataset:
The occurrence of cebollite in kimberlite and included zeolitized crustal xenoliths
Authors: Kruger F. J. 
Published: December 2006

SummaryTwo different parageneses for cebollite, a rare hydrated calcium aluminium silicate, are described, both differing from all previously reported occurrences.Cebollite forms concomitantly with natrolite from plagioclase in xenoliths of crustal material incorporated in kimberlite. The mineral also occurs as a late stage primary mineral in a phlogopite-rich kimberlite.Tentative models for the genesis of the mineral in the environments described are proposed. It is suggested that the final stages in the crystallization of diatreme-facies kimberlite are dominated by fluids rich in lime and having a low partial pressure of CO2.
Petrogenesis of alnöitic rocks from Malaita, Solomon Islands, Melanesia
Authors: Nixon Peter H. , Mitchell Roger H. , Rogers Nicholas W. 
Published: December 2006

SummaryAphanitic and fragmental alnöitic rocks from Malaita contain ultrabasic xenoliths and discrete nodules (megacrysts) of pyroxenes and garnets. Primary minerals in the alnöites are olivine (Fo85), clinopyroxene (diopside-sahlite), natro-melilite (1/3 melilite-2/3 åkermanite), phlogopite (1–9% TiO2), perovskite, spinel (ulvö spinel-magnetite series) and accessory nepheline, melanite, and apatite. Alnöite olivines and clinopyroxenes are compositionally different from those phases in the xenoliths and megacrysts. Rare earth element distribution patterns are linear and indicate strong enrichment in the light rare earths (La/Yb = 42−49). The alnöites are possible primary melts of a pyrolite-type mantle formed by approximately 4% partial melting at depths greater than 120 km, under high carbon dioxide pressures. Despite containing a mantle xenolith assemblage similar to that found in kimberlites, the host Malaita rocks are minera-logically and geochemically different from kimberlite.
Apachite and gilalite, two new copper silicates from Christmas, Arizona
Authors: Cesbron F. P. , Williams S. A. 
Published: December 2006

SummaryBoth new species are retrograde or mesogene minerals that occur in tactites at the Christmas mine, Gila County, Arizona (USA). Gilalite is green, H = 2, D = 2.82. Biaxial (—), 2V small, α = 1.560, β = γ = 1.635. No single crystals found; strongest lines at 13.49 Å, (10); 10.97 (5); 7.786 (5). Analysis gave CuO 36.2%, MgO 2.3, CaO 3.8, MnO 0.5, SiO2 41.5, H2O 14.6, close to Cu5Si6O17·7H2O.Apachite is blue, H = 2, D = 2.80. Biaxial (—), 2V small, α = 1.610, β = γ = 1.650. No single crystals found. Strongest lines are 12.90 Å (10); 3.168 (7); 7.663 (5). Analysis gave CuO 43.6%, FeO 0.3, MgO 1.7, CaO 1.8, SiO2 40.8, H2O 13.8, close to Cu9Si10O29·11H2O.
The aqueous chemistry of uranium minerals. Part 2. Minerals of the liebigite group
Authors: Alwan Alwan K. , Williams Peter A. 
Published: December 2006

SynopsisFree energies of formation of liebigite, Ca2UO2 (Co3)3·10H2O, swartzite, CaMgUO2(Co3)3·12H2O, bayleyite, Mg2UO2(CO3)3·18H2O, and andersonite, Na2CaUO2(CO3)3·6H2O have been determined from solution studies at various temperatures. ΔGf(298.2K)° values for the above minerals are −6226±12, −6607±8, −7924±8 and −5651±24 KJ mol−1 respectively. ΔH0f(298.2K) values respectively are −7037±24, −7535±20, −9192±20, and −5916±36 kJ mol−1. These results have been used to construct the stability diagram for the four minerals shown in fig. I. Andersonite can only form when the activity of the sodium ion, aNa+, is relatively high and aCa2+ and aMg2+ are small. The interconversions of the sodium-free species are defined. When aMg2+/aCa2+ < 0.32 liebigite is the stable phase. If aMg2+/aCa2+ > 7.94, bayleyite forms preferentially. One might therefore expect the bayleyite-andersonite association to be more common than liebigite-andersonite, but this is entirely dependent upon the relative concentrations of Mg2+(aq) and Ca2+(aq) in the solutions from which the minerals form.
The uranium content of garnet lherzolite xenoliths from kimberlites
Authors: Carswell D. A. , Rice C. M. 
Published: December 2006

SummaryUranium contents ranging from 0.03–1.18 ppm have been determined by delayed neutron activation analysis in a suite of 19 ultrabasic xenoliths (mostly of the common garnet lherzolite type) from the kimberlites of southern Africa. Consideration of these and previous data lead us to conclude that the U content of uncontaminated garnet lherzolite in the uppermost mantle is on average roughly 0.04–0.05 ppm, levels which are sufficient to account for the observed U contents of fresh basalts. Higher U contents in mantle-derived ultrabasic xenoliths are the result of secondary alteration processes, most probably related to infiltration metasomatism stemming from contact with kimberlitic or carbonatitic magma fractions. This introduced U is concentrated along the boundaries of the primary mineral grains and is mostly readily removed by acid leaching. A partial analysis is given for a secondary uraniferous calcium phosphate phase observed in kelyphitic rims around garnets.
Anatexis and high-grade metamorphism in the Champira Dome, Malawi: petrological and Rb-Sr studies
Authors: Haslam H. W. , Brewer M. S. , Davis A. E. , Darbyshire D. P. F. 
Published: December 2006

SummaryBanded gneisses and migmatites in the Champira Dome contain assemblages of the biotite-cordierite-almandine subfacies of the granulite facies. The banded gneisses represent a sequence of arkosic sediments metamorphosed to sillimanite-cordierite gneisses. The migmatites were derived from more argillaceous and potassic sediments, with lower oxidation ratios and lower Ba/Rb ratios. They consist of a quartzo-feldspathic leucosome, representing anatectic melt, with schlieren of the refractory minerals sillimanite, garnet, biotite, and oxide minerals. Cordierite developed from garnet and biotite, except in rocks of high FeO/(FeO + MgO) ratio. Both rock types contain assemblages of magnetite + hercynite + corundum + ilmenite + hematite, formed by unmixing of high-temperature solid solutions. Rb-Sr studies of the banded gneisses gave an age of 2327 ± 25 Ma, which is interpreted as the date of metamorphism, and an initial 87Sr/86Sr ratio of 0.7064 ± 0.0003. The migmatite samples plot close to this 2327 Ma regression line, but the strontium isotopes were considerably disturbed, though not homogenized on the scale of sampling, 962 ± 34 Ma ago. It is considered that the anatexis in the migmatites was contemporaneous with the metamorphism of the banded gneisses and that the 962 ± 34 Ma event may be correlated with recrystallization of the migmatites accompanying the growth of cordierite.
Ortho- and clinopyroxenes from the pyroxene granulites of Swat Kohistan, northern Pakistan
Authors: Qasim Jan M. , Howie R. A. 
Published: December 2006

SummaryThis paper presents wet chemical analyses of forty-one pyroxenes (thirty-nine of them new) from pyroxene granulites and a few neighbouring rocks from Swat Kohistan and the adjoining Indus Valley. The granulites, considered to be derived from plutonic norites of an island arc tholeiitic nature, constitute one of the most extensive belts of its kind in the world. The pyroxenes are not unusual in any respect but they bear a closer resemblance to metamorphic than to igneous pyroxenes crystallized from deep-seated tholeiitic magmas. The distribution of Mg, Fe, and Mn (average KDMg−Fe=0.57) and the tie-line intersections on the Wo-En join (generally from Wo80.5to Wo76.5) between the coexisting eighteen pyroxene pairs from the granulites are discussed. Based on eight different methods of geothermometry and other considerations, it is concluded that the pyroxene granulites were metamorphosed at around 800°C and 7 to 8 kbar.
Ferroan carrollites, cobaltian violarites, and other members of the linnaeite group: (Co,Ni, Fe,Cu)3S4
Authors: Riley John F. 
Published: December 2006

SummaryElectron microprobe analyses and X-ray data are given for iron-rich carrollites, cobaltian violarites, and other members of the linnaeite group. The iron-rich carrollites (8.5 wt% Fe) occur as an unmixed phase in a copper linnaeite host from the Zambian Copperbelt. Primary and secondary cobaltian violarites are reported from Rhodesia and Australia respectively with the latter recording up to 19.2 wt% Co. A diagrammatic review is given of the extremes of composition reported within the group together with the more reliable cell sizes.
Analcime from the L. Lias on the W. Somerset coast
Authors: Alabaster C. J. 
Published: December 2006

SummaryAnalcime, occurring both as small, pale-brown trapezohedral crystals and pale-brown slaggy masses, is reported growing into and replacing aragonitic shell debris in a heavily faulted, 15-km long, coastal exposure of L. Jurassic marine sediments. Associated minerals include authigenic baryte, sphalerite, pyrite (some framboidal), celestine, aragonite, calcite, dolomite, quartz, and solid hydrocarbon. No other zeolites have been found. Its modes of occurrence, crystal morphology, and relationships to these minerals are described. The analcime appears to be restricted in occurrence to the W. Somerset coast. Partial chemical analysis of one sample is given. The brown colouration is suggested to be due to organic compounds. XRD analysis of five samples reveals progressive decrease in silica content towards western extremity of the exposure. No evidence of volcanic ash contamination of the sediments is found. A hydrothermal origin is discounted; formation of the analcime by purely diagenetic processes is suggested.
The nickel telluride mineral melonite from the Jaduguda uranium deposit, Singhbhum Shear Zone, Bihar, India
Authors: Krishna Rao N. , Narasimhan D. , Rao G. V. U. 
Published: December 2006

SummaryThe rare nickel telluride mineral melonite is identified from Jaduguda uranium ore, Singhbhum Shear Zone, Bihar, India. Its physical, optical, chemical, and paragenetic characteristics are described. The composition as obtained by EPMA is NiTe1.66Bi0.06 or approximately Ni3(Te,Bi)5. The association of melonite with molybenite in this ore deposit is unusual, since melonite is generally associated with tellurides of gold and silver. This is the first reported occurrence of melonite from India.
Assimilation and metamorphism at a basalt-limestone contact, Tokatoka, New Zealand
Authors: Baker C. K. , Black Philippa M. 
Published: December 2006

SummarySmall-scale assimilation of limestone during the intrusion of an olivine basalt feeder dyke into an Eocene argillaceous, siliceous biomicrite in the Tokatoka area has resulted in the incorporation of large amounts of calcium into the parent magma. Initial effects of assimilation have caused partial resorption of the early-formed igneous mineralogy and the precipitation of calcic, iron-rich clinopyroxenes (ferrosahlite to hedenbergite), wollastonite, schorlomite, and pyrrhotine. Pyroxene compositions show a trend of strong enrichment in Catschermak and ferrosilite components. Derivative hydrothermal solutions, rich in Ca, Si, Al and alkalis have precipitated and altered anhydrous phases to tobermorite, thomsonite, prehnite, pectolite, cebollite, hydrogrossular, gismondine, analcime, Sr- and Ba-bearing zeolites, and calcite.Modelling of the basalt-limestone assimilation process by least-squares mixing methods has shown that the observed chemical variation can largely be accounted for by the dilution of the basalt with up to 30 wt. % decarbonated limestone. Desilication of the liquid, a result of this dilution effect, has been accommodated in the chemistry of the early-formed mineralogy rather than by the crystallization of minerals characteristic of an undersaturated rock type.Contemporaneous with the intrusion of the basalt was the high-temperature contact metamorphism of the limestone. This produced assemblages of rankinite, kilchoanite, larnite, spurrite, grossular, and tobermorite. Subsequent injection of the basalt and hybrid phases into fractures has resulted in the alteration of the primary metamorphic assemblage to wollastonite, scawtite, foshagite, hydrogrossular, calcite, and vaterite.
Morphology, twinning, and optical orientation of gismondine
Authors: Nawaz Rab 
Published: December 2006

SummaryGismondine is a monoclinic mineral but prior to X-ray determination of its unit cell it was variously regarded as orthorhombic, monoclinic, or triclinic on account of its intricate twinning. A study of gismondine crystals from Osa Quarry, near Rome, indicates that the morphologically dominant form is {32} which by twinning about the normal to {100} produces penetration-twinned octahedral crystals united on (100) and (001). Gismondine has poor cleavage on {32} optic plane is (010) and γ:[001] = 42.5° (in obtuseβ).
Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales
Authors: Robinson D. , Nicholls R. A. , Thomas L. J. 
Published: December 2006

SummaryIllite crystallinity determinations on Palaeozoic pelitic rocks, whose stratigraphic range runs from Lower Cambrian to Westphalian, indicate that anchimetamorphism has affected both the Lower and Upper Palaeozoic sequences. Two metamorphic episodes are in evidence, with the earlier, Caledonian, being of slightly higher grade. The higher anchizone crystallinity values are recorded from the Fishguard area in which mineral assemblages of the prehnite-pumpellyite facies have recently been recognized in basic igneous rocks. The later metamorphic episode has affected rocks to the south of the Variscan front. Here crystallinity values are low anchizone but some straddle the boundary with the diagenetic state. The Pembroke coalfield lies in this southern area and has coals largely of anthracite rank with volatile matter contents of between 10.1 and 5% Grade of metamorphism as indicated by crystallinity and by coal rank data from the Pembroke coalfield shows anomalous results to that described from the main South Wales coalfield. A neo-formed 2M illite from the Variscan spaced cleavage is described with analytical and X-ray diffraction data.
Bismutohauchecornite—new name: hauchecornite redefined
Authors: Just J. 
Published: December 2006

SummaryThe name hauchecornite has been applied in the literature to a group of minerals with similar crystal structures and the general formula (Ni,Co,Fe)9ABS8, where A and B are As, Sb, Bi, and Te in two nonequivalent structural sites. A classification of the group is proposed based on the relative abundance of the elements As, Sb, Bi, and Te in the two sites. Hauchecornite is redefined as Ni9BiSbS8, the end-member being closely approximated by the composition of the material from the type locality, and a new name, bismutohauchecornite, is proposed for the Ni9Bi2S8 end-member. The classification, redefinition, and the new name have been approved by the Commission on New Minerals and Mineral Names, IMA.
A re-examination of cheralite
Authors: Bowles J. F. W. , Jobbins E. A. , Young B. R. 
Published: December 2006

SummaryA new analysis of the type material of cheralite specifies the individual rare earth elements. Unit cell contents are: (REE1.58Th1.15Ca1.03Pb0.05U0.15)3.96 (P3.67Si0.33)4.01O16. Refinement of the cell parameters based on new XRD data shows that a = 6.7515 ± 0,0005 Å, b = 6.9625 ± 0.0005, c = 6.468 ± 0.0005, β = 103° 53′, giving a cell volume of 295.2 Å3. Space group P21/n.
The diffusion of Fe2+ ions in spinels with relevance to the process of maghemitization
Authors: Freer W. , O'Reilly R. 
Published: December 2006

SummaryThe maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.
Changes in crystal morphology of synthetic reedmergnerite (NaBSi3O8) during ordering experiments
Authors: Mason R. A. 
Published: December 2006

SummaryThe morphologies of hydrothermally grown reedmergnerite crystals change systematically with time and rate of change of B, Si order. Three stages in this process are recognized: (1) Growth of well-faceted crystals. (2) Development of etching leading to the formation of irregular grains. (3) Modification of irregular grains to form rounded or ellipsoidal crystals. A solutionreprecipitation process is responsible for the morphological changes and the increase in degree of order of B and Si with time at constant temperature and pressure.
An optical anomaly possibly due to optical activity in some uniaxial opaque ore minerals
Authors: Hall A. J. , Cervelle B. D. , Simpson P. R. 
Published: December 2006

SummarySpectral reflectance measurements on three uniaxial ore minerals, tellurium, chalcopyrite, and stibioluzonite, which are opaque at least in the visible part of the spectrum have revealed that the reflectance curve of the ordinary ray varies with crystallographic orientation of the polished section. The three minerals possess symmetries capable of exhibiting optical activity in transmitted light. A possible explanation, therefore, of the anomalous behaviour is that the optical constants, i.e. the refractive index and the absorption coefficient, and thus also the reflectance, of the ordinary ray may differ for sections cut normal to c where optical activity probably has its maximum effect and for sections cut parallel to c where there is probably little or no complication due to optical activity. There would therefore appear to be a need to extend the theory of reflection from absorbing media to include reflection from optically active absorbing minerals.
An evaluation of the performance of an inductively coupled plasma source spectrometer for the determination of the major and trace constituents of silicate rocks and minerals
Authors: Walsh J. N. , Howie R. A. 
Published: December 2006

SummaryThe results of a study on the suitability of the inductively coupled plasma source spectrometer for the analysis of rocks and minerals are presented. The preparation of a stable solution of the elements to be measured is a prerequisite, and methods of sample preparation are described. It is shown that it is possible to measure all the major elements (excluding H2O and Fe2+) with acceptable precision and accuracy, and a wide range of trace elements down to the ppm level in the rock or mineral. Excluding sample preparation time, analysis and print-out of results as percent or ppm requires 1–2 minutes for complete analysis. Data on possible interferences (spectral line overlap etc.) are presented and, using some analyses of rocks and minerals comparisons are made with other analytical methods.
Ferroglaucophane- and chloritoid-bearing metapelites from the phyllite series, southern Peloponnese, Greece
Authors: Katagas Christos 
Published: December 2006

SummaryThe unusual assemblage ferroglaucophane-chloritoid-paragonite-garnet-muscovite-chlorite-quartz has been found in metapelites of the phyllite series, north-east of Neapolis, southern Peloponnese, Greece. The chemical compositions of the coexisting phases are given, and the physical and chemical constraints which may control the appearance of this assemblage are briefly discussed.
The structural role of Fe 3+ in biotites from the Euganean Hills, Italy
Authors: De Pieri Renzo 
Published: December 2006

SummaryPlots of partition coefficient (mineral/matrix) against ionic radius of the elements in seventeen biotites from trachytes and rhyolites of the Euganean Hills do not show differences in the type of diagram between the biotites with tetrahedral sites completely filled by Si and Al, and those in which filling is only possible with the intervention of Fe3+ (or Ti4+) since these sites are incompletely filled by Si and Al. This behaviour seems to exclude, for the latter, the presence of Fe3+ (or Ti4+ in the tetrahedral site. Similar indications are given by structural analysis. The possibility of existence of [(OH)4]4− groups or, more probably, vacancies in these sites is therefore suggested. The consequences that these results would have on the possibility of correct calculation of the crystallo-chemical formula are discussed.
Petrofabrics of laminated gabbros from the Centre 3 igneous complex, Ardnamurchan, Scotland
Authors: Fortey N. J. 
Published: December 2006

SummaryPetrofabric analysis of five specimens of laminated gabbro from the Centre 3 igneous complex, Ardnamurchan, was carried out by measuring orientations of grains of plagioclase, olivine, and augite with a Universal-stage. Linear alignments of primary precipitate mineral grains within the laminar fabrics were revealed by plots of data for coexisting plagioclase and olivine or augite. The plagioclase grains involved have tabular forms elongated parallel to their a-axes (rather than their c-axes). The olivine grains have flattened ovoid forms and the augite grains have sub-ophitic forms developed about prismatic primocrysts. In all specimens plagioclase displayed alignment of long grain-axes directed approximately down the dip of the lamination, save for one case in which a weak oblique alignment was observed. These lineations were reproduced by accompanying olivine and augite. The alignments are tentatively ascribed to flowage of a viscous boundary zone to the magma body in which crystal growth was taking place.
Hibonite and coexisting zoisite and clinozoisite in a calc-silicate granulite from southern Tanzania
Authors: Maaskant P. , Coolen J. J. M. M. M. , Burke E. A. J. 
Published: December 2006

SummaryThe third terrestrial occurrence of hibonite is reported from granulite-facies rocks in the Furua Granulite Complex in southern Tanzania. The mineral forms yellowish-brown lath-shaped crystals in a grossular-anorthite rock containing subordinate sphene (clino)zoisite, hercynite, apatite, ilmenite, and corundumilmenite intergrowths.Electron-microprobe analyses indicate a generalized formula (Ca1−xREx)[(Al,Fe3+)12−2a+x(Ti,Si)(Ti,Si)a−x(Fe2+, Mg)a]O19, with RE = Ce + La + Nd, x = 0.2, and a = 0.8. Individual mineral analyses show a cation substitution of Ca + Ti + Fe3+ = RE + 2Al. Relatively high RE and Fe contents represent the main chemical differences with meteoritic hibonite. The hexagonal unit cell has a = 5.61 Å, c = 22.18, in good agreement with the other terrestrial hibonites.Three compositional types of (clino)zoisite are distinguished: 1.8–3.1 wt% Fe2O3 (orthorhombic and monoclinic), 3.9–6.0 wt% Fe2O3 (monoclinic), and 5.8–7.9 wt% Fe2O3 with an average of 6.3 wt% RE2O3 (monoclinic).Thermometric and barometric data for coexisting pyroxenes and garnet from adjacent rocks indicate granulite-facies equilibration conditions of 750 to 850 °C and 6 to 11 kb. During retrogression with increasing partial H2O pressures, hibonite reacted with plagioclase and garnet to form spinel, sphene, and RE-bearing clinozoisite. Corundum-ilmenite inter-growths probably resulted from the breakdown of an Fe-högbomite.