bluuebunny/crossref_metadata_2025_split huggingface dataset:
Muscovite breakdown and corundum growth at anomalously low fH2o: a study of contact metamorphism and convective fluid movement around the Omey granite, Connemara, Ireland
Authors: Ferguson Colin C. , Al-Ameen Sanaa I. 
Published: December 2006

AbstractIn the aureole of the late Caledonian Omey granite corundum develops in the Dalradian country rocks in a zone up to 250 m from the granite contact. The distribution of andalusite and K-feldspar in pelites and calcite+wollastonite+grossularite in marbles is consistent with inner-aureole metamorphic conditions of 615±25°C at 2.5±0.25 kbar, and ⋍ 0.85. Corundum develops from the reaction muscovite → corundum + K-feldspar+H2O and first appears over 100 m further from the granite than the assemblage wollastonite + grossularite + anorthite. Experimentally determined equilibria can be satisfied only if for the corundum-producing reaction was less than 0.6 and perhaps as low as 0.4. Corundum always grows within large muscovite crystals;fH2O within the crystal lattice is unrelated to that in the grain-boundary fluid of the surrounding rock.Although whole-rock oxidation ratios are irregularly distributed within the aureole they are uniformly low in corundum-bearing rocks. Reducing conditions probably resulted from localized flow of H2O-rich fluid away from the granite in a diffuse channelway that contains most of the corundum localities and also a distinctive skarn. Although corundum growth within muscovite is sealed off from the external water vapour conditions, it is suggested that movement of H2O down a thermal gradient (and hence down an fH2O gradient at constant pressure) promotes the escape of (OH)− from the muscovite lattice and so allows the corundum reaction to proceed.
K-Na exchange equilibria between muscovite-paragonite solid solution and hydrothermal chloride solutions
Authors: Pascal M. L. , Roux J. 
Published: December 2006

AbstractThree ion exchange equilibrium isotherms between muscovite-paragonite solid solution and 2-molal KCl-NaCl aqueous solutions have been studied at (1) 420°C 1 kbar, (2) 420°C, 2 kbar, and (3) 550°C, 2 kbar. The ΔG°(Joules) ± 2σ of the ion exchange reaction are: ΔG° (1) = −17 259±686, ΔG° (2) = −18 268 ± 560, ΔG° (3) = −16018 ± 336. The excess mixing parameters (‘subregular solution’) of the solid solution (at 1 bar) have been calculated:The corresponding binodal compositions are (muscovite mol fraction): 12–56% at 420 °C, 1 bar and 15–51% at 550 °C 1 bar. The compositions of micas in equilibrium with perthites (high structural state) at 400, 500, 600 °C and 2 kbar are respectively:Xmus= 91, 86, and 82%.The mixing properties of the solution were estimated using the speciation of two molal chloride solutions calculated from the dissociation constants of NaCl and KCl in aqueous solution. Although NaCl appears to be substantially more dissociated than KCl, the resulting excess free energy of mixing of the hydrothermal (Na,K)Cl solution was found less than 500 J at temperatures above 400 °C and pressures up to 2 kbar.The difference in Gibbs free energy of formation (from the elements at 25 °C, 1 bar) between NaCl and KCl in two molal aqueous solutions is proposed:
Zirconolite and baddeleyite from metacarbonates of the Oetzstal–Stubai Complex (northern Tyrol, Austria)
Authors: Purtscheller F. , Tessadri R. 
Published: December 2006

AbstractZirconolite and baddeleyite from polymetamorphosed metacarbonates of the Oetztal-Stubai complex (northern Tyrol, Austria) are described in terms of their paragenetic relationship and chemical compositions. For the first time an analysis of a chemically zoned niobian zirconolite (high Nb and low Ti in core, low Nb and high Ti at rim) is presented. Genetic possibilities for the origin of the metacarbonates are discussed in the light of zirconolite- and baddeleyite-formation.
The accuracy of X-ray diffraction methods for determining mineral mixtures
Authors: Brime Covadonga 
Published: December 2006

AbstractAn X-ray diffraction method has been successfully applied to the quantitative determination of mineral mixtures. The absorptive properties of the samples and the number of components determine the analytical procedure to be used. The methods described (external standard plus empirical determination of the mass attenuation coefficient) provides an accurate and rapid alternative to the direct measurement of the mass attenuation, Compton diffusion or internal standard methods. The relative accuracy obtained is of the order of 10% at the 0.1% level, independent of the sample composition.
Effects of resolution on the measurement of grain ‘size’
Authors: Dearnley R. 
Published: December 2006

AbstractMeasurements of fine-grained dolerites by optical automatic image analysis are used to illustrate the effects of magnification and resolution on the values obtained for grain ‘size’, grain boundary length, surface area per unit volume, and other parameters. Within the measured range of optical magnifications (× 26 to × 3571) and resolutions (1.20 × 10−3 cm to 8.50 × 10−6 cm), it is found that the values of all grain parameters estimated by chord size analysis vary with magnification. These results are interpreted in terms of the concepts of ‘fractal dimensions’ introduced by Mandelbrot (1967, 1977). For some comparative purposes the fractal relationships may be of little significance as relative changes of size, surface area, and other parameters can be expressed adequately at given magnification(s). But for many studies, for instance in kinetics of grain growth, the actual diameter or surface area per unit volume is an important dimension. The consequences are disconcerting and suggest that it may be difficult in some instances to specify the ‘true’ measurements of various characteristics of fine-grained aggregates.
Niccolite-magnetite mineralization from Upper Teesdale, North Pennines
Authors: Young B. , Styles M. T. , Berridge N. G. 
Published: December 2006

AbstractNiccolite and other nickel-bearing minerals have been found in magnetite-rich ore at Lady's Rake Mine [NY 8063 3414] in the North Pennines 5.5 km NW of Langdon Beck, Teesdale, Co. Durham. Associated ore minerals include galena, sphalerite, chalcopyrite, pyrite, and pyrrhotite. Similar magnetite-rich ores, in places bearing ugrandite garnets, have been located at two nearby localities, though without nickel minerals. Petrographic study indicates that this unusual assemblage developed in a skarn environment, probably related to the intrusion of the Whin Sill. Field evidence suggests an association with the Teesdale Fault system. Electron microprobe analyses show that Lady's Rake niccolite is near to end-member composition: analyses of other North Pennine niccolites show up to 25 at. % substitution of S and Sb for As.
New data on glaucocerinite
Authors: Raade Gunnar , Elliott C. J. , Din V. K. 
Published: December 2006

AbstractThe strongest lines in the X-ray powder diffraction pattern of type material of glaucocerinite from Laurion (Greece), indexed on a hexagonal pseudocell, are 10.9 (100) (003), 5.45 (90) (006), 3.63 (80) (009), 2.62 (60) (012), 2.46 (60) (015), 2.231 (50) (018), and 1.981 Å (50) (0.1.11). The pseudocell parameters are a 3.0700(8), c 32.65(1) Å. Chemical analysis of topotype material yields the formula [(Zn,Cu)5Al3(OH)16] [(SO4)1.5·9H2O] based on a pyroaurite-like structure. The pseudocell parameters for this sample are a 3.057(3), c 32.52(5) Å. Optical data are 2Vα ⋍ 60°, α 1.540, β 1.554, γ 1.562; D(meas.) = 2.4±0.1 g/cm3, D(calc.) = 2.33 g/cm3. So-called ‘woodwardite’ from Caernarvonshire, Wales, is identified as the Cuanalogue of glaucocerinite. An ‘11 Å mineral’ occurring together with carrboydite in Western Australia is shown to be the Ni-analogue of glaucocerinite. Alleged cotype glaucocerinite from Laurion is related to woodwardite and has the formula [(Zn,Cu)2Al(OH)6][(SO4)0.5 · 3H2O]. This is a cation-ordered pyroaurite-type structure with hexagonal cell parameters a 5.306(2), c 26.77(2) Å. The strongest X-ray powder lines occur at 8.9 (100) (003), 4.47 (90) (006), 2.55 (60) (113), and 2.28 Å (50) (116).
The Tugtutôq older giant dyke complex: mineralogy and geochemistry of an alkali gabbro-augite-syenite-foyaite association in the Gardar Province of South Greenland
Authors: Upton B. G. J. , Stephenson D. , Martin A. R. 
Published: December 2006

AbstractThe Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicatefO2andTvalues just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations andREEpatterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.
Radioelement abundance data for some Dalradian rocks from Co. Donegal, Ireland
Authors: O'Connor P. J. , Long C. B. 
Published: December 2006

AbstractData for U, Th, and K, determined by epithermal neutron activation methods, are reported for Lower and Middle Dalradian lithologies from Co. Donegal, Ireland. Abundances are identical to rocks with stratigraphical correlation in the Scottish Dalradian and appear not to have been affected by regional metamorphism to biotite and possibly even garnet grade during the Grampian orogenic phase, or later contact metamorphism in the aureole of the Main Donegal pluton. Uraniferous Dalradian lithologies have not been encountered in Donegal. Incorporation of Dalradian rocks, either by assimilation or as extensive raft trains within the Main Donegal granite, is therefore unlikely to have contributed to the development of known pegmatite-hosted U mineralization associated with this late Caledonian pluton.
Pb-Zn and minor U mineralization at Tyndrum, Scotland
Authors: Pattrick Richard A. D. 
Published: December 2006

AbstractThe Tyndrum Pb-Zn mineralization occurs as veins and vein breccias in NE-SW trending fractures associated with the Tyndrum-Glen-Fyne fault. The major minerals are quartz, galena, and sphalerite with minor chalcopyrite and baryte. Tetrahedrite (sometimes silver-and cadmium-rich), pyrargyrite, marcasite, and pyrite occur as small inclusions (< 100 µm) in the galena-rich veins. Sphalerite formed early in the depositional sequence, mainly in breccias, with increasing amounts of galena and chalcopyrite deposited in the later vein stages of mineralization. Uraniferous veins post-date the main Pb-Zn mineralization and contain uraninite, calcite, baryte, galena, sphalerite, chalcopyrite, argentite, chalcocite, tetrahedrite, and safflorite.Fluid inclusion studies reveal that the mineralizing solutions contained c.20 wt. % equivalent NaCl + KCl, had an Na/K ratio of 3 : 1 and were boiling during mineral precipitation.The Tyndrum fault controlled the upward flow of the hydrothermal solutions and its intersection with fractures in quartzites favoured the siting of the veins. The depositional sequence is explained by an increase in temperature during the mineralizing episode. The uraniferous veins may be a late oxidized stage of the main Pb-Zn mineralization.
The rates of dissolution of olivine, plagioclase, and quartz in a basalt melt
Authors: Donaldson Colin H. 
Published: December 2006

AbstractThe dissolution rates of spheres of two magnesian olivines, two plagioclases, and quartz in tholeiitic basalt have been determined at three super-liquidus temperatures and one-atmosphere pressure. There are considerable differences in the rates among the minerals, e.g. at 1210°, 12° above the liquidus temperature of the basalt, labradorite dissolves at 86 µm/h. and the magnesian olivines at 9 and 14 µm/h. The rates are not time dependent and this, coupled with the existence of concentration gradients in the composition of quenched melt adjacent to partially dissolved crystals, indicates that the dissolution rates are dictated by a combination of diffusion and convection of components to and from the crystal-liquid interface. Values for the activation enthalpy of dissolution are small for quartz and plagioclase (40–50 kcal mol−1) but large for olivine 73–118 kcal mol−1). Dissolution of plagioclase in rock melts seems to be a much more rapid process than crystal growth, whereas olivines apparently dissolve and grow at similar rates. Crystal dissolution is sufficiently slow that ascending, crystal-bearing magma may become superheated and yet fail to dissolve the crystal fraction before quenching; this may be the reason that olivine phenocrysts are often rounded.
Potassium pargasite from Einstödingen, Lützow-Holm Bay, East Antarctica
Authors: Matsubara S. , Motoyosh Y. 
Published: December 2006

AbstractPotassium pargasite containing 3.19 wt. % K2O was found in a skarn from the islet of Einstödingen, Lützow-Holm Bay, East Antarctica, together with some high potassium pargasitic amphiboles. A positive correlation is shown between Fe2+/(Mg+Fe2+) and K/(K + Na(A)) ratios in pargasitic amphiboles suggesting that the increase of Fe2+ serve to stabilize high-K pargasites under the metamorphic conditions of the granulite facies.
Hydroxyl-bastnaesite-(Nd), a new mineral from Montenegro, Yugoslavia
Authors: Maksimović Zoran , Pantó György 
Published: December 2006

AbstractHydroxyl-bastnaesite-(Nd), the Nd- and OH-dominant new member of the bastnaesite group, has been found in the red karstic bauxites near Nikšić, Montenegro. It occurs as whitish, irregular aggregates of crystals usually 100–200 µm in diameter. Hexagonal with the cell dimensions a = 7.191 and c = 9.921 Å, with Z = 6. The strongest lines of the X-ray powder diffraction pattern (d, I, hkl) are: 4.95 80(002); 3.596 79(110); 2.911 100(112); 2.077 29(300); 2.042 51(114); 1.914 30(302). The mineral is uniaxial positive, ω 1.715, ɛ 1.81; Dcalc 4.89 g/cm3.Electron probe analysis, using garnet, apatite and synthetic glass standards, combined with thermogravimetric and evolved gas analysis, gave Y2O3 0.2, La2O3 27.1, Ce2O3 0.3, Pr2O3 8.5, Nd2O3 31.5, Sm2O3 4.4, Eu2O3 1.3, Gd2O3 1.4, CaO 0.3, F 3.3, H2O 2.26, CO2 20.63, sum 101.19, less O = F 1.39, total 99.80%. This analysis calculates to (Nd0.41La0.36Pr0.11Sm0.06Gd0.02 Eu0.02Ca0.01)Σ0.99(CO3)1.03[(OH)0.55F0.38]Σ0.93, or ideally, (Nd,La)CO3(OH,F), with Nd > La and OH > F.
Tourmalinization in the Skiddaw Group around Crummock Water, English Lake District
Authors: Fortey N. J. , Cooper D. C. 
Published: December 2006

AbstractVeins of tourmalinite were formed by wallrock alteration adjacent to steep fractures in bleached, indurated Skiddaw Group metasedimentary rocks around Crummock Water, north-west Lake District. The vein rock is a fine-grained granoblastic mosaic of tourmaline, quartz, and minor rutile in which bedding is preserved. Brecciation, in which tourmalinite fragments are set in a coarser quartz-tourmaline matrix, is present in some veins. Networks of cross-cutting quartz veinlets with tourmaline, chlorite, and muscovite are very common. The tourmaline is intermediate schorl dravite and mostly brown in plane polarized light, though prisms in breccia matrix and veinlets have blue, low-Ti cores and brown rims. Comparison of tourmalinite and host-rock analyses indicates almost complete loss during tourmalinization of K, Rb, Li, Ba, As, and La, plus depletion in Ce, Y, Na, Sr, P, and Mn. The elements Si, B, Mo, and erratically, minor F, W, and Sn were introduced. Cu, Pb, Zn, and Ca show both gains and losses probably due to initial depletion and subsequent local enrichment. Reduction in Al, Zr, and Ti concentrations relates to dilution by introduced silica. The tourmalinite veins were formed by the action of hydrothermal fluids derived from the concealed late-Caledonian granitic intrusion responsible for the thermal metamorphism of the country rocks.
Stability relations of malachite and azurite
Authors: Vink B. W. 
Published: December 2006

AbstractStability relations of malachite and azurite are calculated and shown in Eh-pH diagrams, using ΔF (Gibbs free energy) values listed in Garrels and Christ (1965). The malachite/azurite transition is very sensitive to small chemical changes in the environment: equilibrium is reached at PCO2 = 10−3.45 atm., i.e. close to normal values, whereas the precipitation of both minerals from cupric-ion-bearing solutions takes place at pH values between 6 and 8, depending CO2 partial pressures. It is shown that stability relations of these minerals can be better explained in terms of activities of the carbonate and bicarbonate ion.Azurite can be formed only under relatively acid conditions at relatively high carbonate activities. Since the latter imply mostly basic conditions, this explains why malachite is the more common form of copper carbonate and that azurite can be formed only under rather unusual conditions. It also explains the frequent alteration of azurite into malachite, due to small changes in carbonate/bicarbonate activities. These alterations include pseudomorphs of malachite after azurite.
Zinc-manganese carbonates from Broken Hill, New South Wales
Authors: Birch W. D. 
Published: December 2006

AbstractSpecimens of honey-brown to pinkish-brown globular carbonates encrusting concretionary goethite–coronadite from the oxidized zone at Broken Hill, New South Wales, have compositions in the rhodochrosite–smithsonite series. This may be the first extensive natural occurrence of this solid-solution series. Growth of the carbonates occurred in zones which have near uniform composition. The ratio MnCO3/(MnCO3 + ZnCO3) for each zone bears a linear relationship to the measured d spacing for the 104 X-ray reflections. Because cerussite is the only other mineral associated with the Zn-Mn carbonates and because of an absence of detailed locality information, the paragenetic significance of these minerals cannot be determined. The solutions depositing them may have been derived from the near-surface equivalents of the Zinc Lode horizons.
The mafic mineralogy of the peralkaline syenites and granites of the Mulanje complex, Malawi
Authors: Platt R. Garth , Woolley Alan R. 
Published: December 2006

AbstractStudies of the mafic mineralogy of the Mulanje granite-quartz-syenite-syenite Massif of southern Malawi delineate two mineralogically distinct complexes—the Main complex and the Chambe complex. Each complex is associated with its own trend of pyroxene evolution. The Main complex pyroxenes exhibit initial enrichment in hedenbergite before subsequent enrichment in acmite (i.e. sodic-salite-sodic-hedenbergite-aegirine-hedenbergite-aegirine), whereas the Chambe pyroxenes display constantly increasing acmite content with no significant enrichment in hedenbergite (i.e. sodic-salite-aegirine-augite-aegirine). This phenomenon is also reflected in the more Mg-rich amphiboles and biotites of the Chambe rocks when compared to those of the Main complex.The general evolutionary trend of the Main complex amphiboles is katophorite → ferroricherite → arfvedsonite which broadly correlates with a change in rock type from syenite to granite. Superimposed on this trend is an essentially similar, yet less extensive trend of the more Mg-rich Chambe amphiboles. The micas of both complexes show a general evolution to more iron-rich compositions with relatively constant Al content. Those of the Main complex, however, display extreme iron enrichment with ultimate formation of essentially pure ferrous annite.Aenigmatite, astrophyllite, fayalite, chevkinite, yttrofluorite, and unidentified RE minerals are characteristic of the Main complex rocks but totally absent from those of the Chambe complex. Ilmenite constitutes the only iron oxide phase in the Main complex rocks whereas titaniferous magnetite (now unmixed) and ilmenite are both present in the rocks of Chambe.The differences between the two complexes are explained in terms of oxygen fugacity, silica activity, crystallization interval, and the relative rates of development of peralkalinity. In essence, the Chambe magmas are considered to have crystallized under high fO2 conditions with an earlier development of peralkaline tendencies when compared to those of the Main complex magmas. Moreover, a lower initial silica activity, a smaller alkali to alumina ratio, and a correspondingly smaller crystallization interval could account for the lack of highly evolved granitic magmas in the Chambe complex, whereas such magmas are integral in the evolution of the Main complex.
Ranciéite from Mazzano Romano (Latium, Italy)
Authors: Barrese Eugenio , Giampaolo Ciriaco , Grubessi Odino , Mottana Annibale 
Published: December 2006

AbstractRanciéite occurs as stalactites coated with 10 Å halloysite in an open fissure crossing the Mazzano Romano Mn-impregnated tuffs. Chemical analysis (by EMPA) gave: MnO2 71.9, CaO 6.11, BaO 2.85, MgO 1.53, K2O 0.86, Na2O 0.53 plus minor oxides, total 85.07% (average of sixteen spots). Thermal analysis gave a total loss of ∼ 20 wt% of which 13.9% can be attributed to bonded water. The resulting formula contains 4H2O rather than 3H2O, as in most published references. The loss of water leads to the formation of hausmannite plus unidentified phases, after a complex sequence of reactions. Dehydration is directly followed by an X-ray amorphous stage. The X-ray pattern and IR spectrum indicate a poor structural order, in agreement with the likely formation conditions of the Mazzano ranciéite at atmospheric pressure and very low temperatures (less than 50 °C), from cold water percolating through the main Mn deposit.