bluuebunny/crossref_metadata_2025_split huggingface dataset:
An unusual sapphire–zircon–magnetite xenolith from the Chanthaburi Gem Province, Thailand
Authors: Coenraads Robert R. , Vichit Pongsak , Sutherland F. Lin 
Published: December 2006

AbstractA sapphire, zircon and magnetite-bearing xenolith from Khao Wua, near Chanthaburi in Thailand, conclusively demonstrates a common origin for the sapphire, zircon and magnetite found in alluvial deposits in the Chanthaburi gem fields. The original aluminium- and titanium-rich octahedral magnetite crystal in the xenolith exsolved into hercynite, magnetite and hematite during cooling. It includes minor anhedral jarosite–alunite, possibly originating as an iron-sulphide-rich immiscible liquid. Uranium-lead isotope dating of zircon in the xenolith gives an age of 1–2 (± <1) million years (Ma). This falls within fission track ages for alluvial zircons (2.57 ± 0.20 Ma) from the Chanthaburi—Trat gem fields and within the potassium-argon ages of 0.44 to 3.0 Ma for the alkali basaltic volcanism in the Chanthaburi Province. These data suggest a common origin for sapphire, zircon and magnetite, and link them with the processes involved in alkali basaltic magma generation. The high iron and zirconium, low magnesium, and the inferred sulphides suggest pegmatite-like crystallization in an incompatible-element enriched, silica-poor magma (partial melt or fractionation product) in the deep crust or upper mantle. Etch features on exposed surfaces of the xenolith indicate that it was transported out of its equilibrium environment by the rise of later magma.
Influence of the mode and distribution of garnet and biotite on Grt-Bt thermometry: evidence from a single-sample case study
Authors: Owen J. V. , Greenough J. D. 
Published: December 2006

AbstractDetailed microprobe and modal data for a sample of layered, garnetiferous, quartzose paragneiss reveal significant differences in garnet-biotite Mg-Fe distribution coefficients (Kd) — and hence paleotemperatures — determined for leucocratic (modal Grt+Bt<25 vol.%) and mesocratic (Grt+Bt> 25 vol.%) layers. In leucocratic layers, lnKd determined from both the core and rim compositions of minerals shows a range of values that varies sympathetically with the absolute amount of garnet and biotite, and, as demonstrated in other studies, inversely with the distance separating both minerals. Due to the small size (<2 mm) of garnets, which facilitated diffusional re-equilibration during cooling from peak metamorphic temperature, lnKd does not correlate to modal Bt/Grt ratios. The largest garnets, which occur in mesocratic layers, nonetheless tend to preserve the most pronounced (retrograde) zoning patterns (i.e. rimward increase in Fe/Mg), consequently mineral core composition lnKd values correlate with grain diameter except where garnets contain abundant biotite inclusions. The highest Grt-Bt temperatures (∼700°C are recorded by: (1) the composition of relatively widely-separated (>0.3 mm) grains in highly leucocratic layers; and (2) the core compositions of relatively large (>1 mm), inclusion-free grains in mesocratic layers. More closely spaced garnets and biotites in leucocratic layers, and small grains in mesocratic layers, give a range of temperatures intermediate between Tmax and diffusional blocking temperatures (∼ 560°C) recorded by the rim compositions of contiguous grains.
Kusachiite, CuBi2O4, a new mineral from Fuka, Okayama Prefecture, Japan
Authors: Henmi Chiyoko 
Published: December 2006

AbstractKusachiite, CuBi2O4, has been found in a calcite vein cutting gehlenite-spurrite skarns at Fuka, Okayama Prefecture. It is associated with calcite, henmilite, sillenite, bakerite, tenolite, bultfonteinite, apophyllite, cuspidine and thaumasite. Kusachiite occurs as prismatic crystals or globular aggregates of platy crystals. It is black, opaque with a metallic lustre. Kusachiite is tetragonal with space group P4/ncc, a = 8.511(2), c = 5.823(2) Å, Z = 4. The strongest lines in the X-ray powder pattern [d in Å (I)(hkl)] are 3.191 (100)(211), 2.695 (18)(310), 1.947 (18)(411), 4.26 (17)(200), 2.913 (16)(002), 2.404 (13)(202), 1.728 (12)(213), and 1.652 (9)(332). The Mohs hardness is 4.5, and the density is 8.5(3) g/cm3 (meas.) and 8.64 g/cm3 (calc.). Cleavage is perfect on {110}. Six electron probe analyses gave the following mean values CuO 13.91, Bi2O3 86.00 and total 99.91 in wt.%. The empirical formula calculated on the basis of O = 4 is Cu0.960Bi2.027O4 with the simplified formula CuBi2O4.
Computer simulation of a microstructure in a potassium feldspar
Authors: Tsatskis I. , Salje E. K. H. 
Published: December 2006

AbstractKinetics of atomic ordering in a potassium feldspar is simulated using massively parallel computing. The simulation method is based on the Monte Carlo algorithm for the Al-Si redistribution (the Kawasaki dynamics) combined with the lattice relaxation. The Hamiltonian has the symbolic formwhere u represents displacements of atoms from ideal positions, and p the Al and Si occupation numbers. The model is purely elastic; there is no direct interaction between Al and Si atoms. The simulated crystal is a thin film with (010) surfaces and consists of 64 × 64 unit cells; the unit cell defined for the whole film contains slightly more than 4 formula units. The (010) orientation is chosen in order to preserve in the film the main structural feature of feldspars: crankshaft-like sheets formed by four-tetrahedra rings. This makes it possible to observe the Pericline twins only. At the late stage of the kinetic run these twins are clearly seen. The direction for the domain walls is determined by the spontaneous strain and changes with the change of the model parameters; considerable local deviations from this direction are observed.
Rigid unit modes in framework silicates
Authors: Dove Martin T. , Heine Volker , Hammonds Kenton D. 
Published: December 2006

AbstractWe describe a model for framework silicates in which the SiO4 (and AlO4) tetrahedra are treated as perfectly rigid and freely jointed. From this model we are able to identify low-energy modes of distortion of the structure, which we call Rigid unit modes. These modes can act as soft modes to allow easy distortions at phase transition. We discuss three forces that will operate at a phase transition in conjunction with the candidate soft modes to determine which of the rigid unit modes will actually precipitate a phase transition, and illustrate these ideas by detailed discussions of the phase transitions in quartz, leucite and cristobalite. The model can also be used to estimate the transition temperature, and the theory highlights an important role for the stiffness of the tetrahedra.
Synthesis and Rietveld crystal structure refinement of mackinawite, tetragonal FeS
Authors: Lennie A. R. , Redfern S. A. T. , Schofield P. F. , Vaughan D. J. 
Published: December 2006

AbstractMackinawite, tetragonal FeS, has been synthesised by reacting iron with Na2S solutions. A Rietveld structure refinement of X-ray powder diffraction data, recorded using X-rays monochromated from synchrotron radiation with a wavelength of 0.6023 Å, has been performed. The structure has been refined in the tetragonal space group,P4/nmm, and has the following cell parameters:a= 3.6735(4),c= 5.0328(7) Å, V = 67.914(24) Å3. Our refinement shows that the FeS4tetrahedron in mackinawite is almost perfectly regular, with a much smaller distortion than has been previously reported. An improved X-ray diffraction data set is provided.
The system Pd-Fe-Ni-S at 900 and 725°C
Authors: Makovicky Emil , Karup-Møller Sven 
Published: December 2006

AbstractThe system Pd-Fe-Ni-S was studied at 900 and 725°C by means of dry condensed charges. At both temperatures it is dominated by the phase relationships involving sulphide melt. Pd-Fe-Ni alloys with broad miscibility primarily coexist with the melt; they are relatively enriched in Pd, whereas the associated melt is enriched in Ni. With decreasing temperature the melt recedes from Fe-rich regions. The incompatibility of PdS (extensive solid solution with Ni) andmssat 900°C is replaced by their co-crystallization (± disulphide(s) of Ni,Fe or ± sulphide melt) at 725°C The Ni/Fe ratio in the melt changes regularly against that inmsswith increasing S fugacity and Pd contents in these two phases. (Ni,Fe)3±xS2and Pd4S play important roles at 725°C. The data offer an array of distribution coefficients and solubility values suitable for geological interpretations.
High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions
Authors: Watt Gordon R. 
Published: December 2006

AbstractMonazite is a light rare-earth element (LREE)-bearing accessory phase common in felsic granitic rocks, and strongly influences LREE concentrations in granites and the chemistry of melts and residues formed during partial melting. Cheralite-rich (high-Th) monazite-(Ce) has been recorded as rims on partially dissolved cores in a suite of granulite-facies migmatites generated by disequilibrium melting. High-Th monazite has previously been recorded only in granitic-pegmatite occurrences. Subidiomorphic monazite-(Ce) from leucosome, melanosome and mesosome consists of complexly zoned cores (up to 300 µm in diameter) containing 5.17–9.87 wt.% ThO2, overgrown by essentially unzoned rims (containing up to 21.4 wt.% ThO2). Uranium contents are average for Th-rich monazite-(Ce) (0.22–3.17 wt.% UO2). Th enrichment (relative to LREE) in monazite-(Ce) rims is ascribed to the presence of fluorine-bearing melts (formed during the incongruent breakdown of biotite to produce a water-undersaturated melt), allowing the formation of REE-fluoride complexes in the melt, coupled with the increased charge balanced substitutions Th4+ + Si4+ ⇌ REE3+ + P5+ and Th4+ + Ca2+ ⇌ 2REE3+ into monazite-(Ce). Fractionation of Th and U (reflected by an increased in Th/U in rims relative to cores) may have occurred due to the removal by a CO2-rich fluid phase in the melt. These interpretations are consistent with elevated CO2 and F contents of granitic liquids produced during the water-undersaturated breakdown of biotite under granulite-facies conditions. Evidence for restricted monazite-(Ce)-melt equilibration and rapid melt removal is provided by the ubiquitous presence of partially embayed cores and unzoned rims.
Anorthite megacrysts from island arc basalts
Authors: Kimata Mitsuyoshi , Nishida Norimasa , Shimizu Masahiro , Saito Shizuo , Matsui Tomoaki , Arakawa Yoji 
Published: December 2006

AbstractAnorthite megacrysts are common in basalts from the Japanese Island Arc, and signally rare in other global fields. These anorthites are 1 to 3 cm in size and often contain several corroded Mg-olivine inclusions. The megacrysts generally range from An94Ab4Ot2 to An89Ab6Ot5 (Ot: other minor end-members, including CaFeSi3O8, CaMgSi3O8, AlAl3SiO8, □Si4O8) and show no chemical zoning. They often show parting. Redclouded megacrysts contain microcrystals of native copper with a distribution reminiscent of the shape of a planetary nebula. Hydrocarbons are also present, both in the anorthite megacrysts and in the olivines included within them. Implications of lateral variations in the Fe/Mg ratio of the included olivines, in Sr-content and in Sr-isotope ratio of the anorthite megacrysts with respect to the Japanese island arc, relate to mixing of crustal components and subducted slab-sediments into the basaltic magmas.
Distribution of trace elements in feldspars of granitic aplites and pegmatites from Alijó-Sanfins, northern Portugal
Authors: Neiva A. M. R. 
Published: December 2006

AbstractAt Alijó-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization. Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Ba, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.
Excess free energies of mixing of Sr,Ba-bearing binary feldspar solid solutions (experimental data)
Authors: Kotelnikov A. R. , Chernysheva I. V. 
Published: December 2006

AbstractThe distribution of potassium and strontium, potassium and barium between feldspars and aqueous chloride solutions was studied at 700°C, 2 kbar and 800°C, 2 kbar respectively. The distribution of Sr and Ba between coexisting feldspar and chloride solutions is not ideal; Sr and Ba are enriched in feldspar relative to solution. In order to estimate the phase state of the chloride solutions, special experiments were conducted using the synthetic fluid-inclusion method in the systems KCl-BaCl2-H2O and KCl-SrCl2-H2O at 700–800°C, 2 kbar. It was shown that (0.5M KCl+0.5M SrCl2) aqueous solution is homogeneous at 800°C, 2 kbar. The 0.25–0.5M SrCl2 solutions are homogeneous at 700°C 2, kbar. The (0.5M KCl+0.5M BaCl2) solution is homogeneous at 700°C, 2 kbar and heterogeneous at 800°C, 2 kbar. Margules parameters for describing the excess energy of mixing of the (K,Sr)- and (K,Ba)-feldspar solid solutions were calculated. The integrated values of excess energy of mixing () were estimated for the different binary feldspar solid solutions, and a correlation of with the crystallochemical parameter ρ = (RA-RB)/D(Me-O) was observed. Feldspar solid solutions can be subdivided into three groups based on the relationship between , p and the stability of the solid solution.
Photo-emission electron microscopy (PEEM) heating investigations of a natural amphibole sample
Authors: Wartho J.-A. 
Published: December 2006

AbstractPEEM allows ‘real-time’ observations to be made of solid-state transformations and other high-temperature processes taking place during vacuum-heating up to c. 2000°C The solid state transformations of an amphibole-rich hornblendite specimen have been observed in the temperature range of 750–1000°C (± 50°C Between c. 970–990°C a rapid change in orientation contrast was observed, indicating a structural rearrangement from an oxyhornblende crystal lattice to a clinopyroxene structure. This phase retains the original amphibole shape and texture (including two 120°C intersecting cleavage traces), but possesses a clinopyroxene crystal structure. At higher temperatures this phase is seen to decompose, forming iron oxides and other fine-grained products. PEEM has provided useful information on both the nature and rates of transformation of natural amphiboles which has proved invaluable in our understanding of the mineralogically-controlled mechanisms of argon release during 40Ar/39Ar dating of amphibole samples.
Kintoreite, PbFe3(PO4)2(OH,H2O)6, a new mineral of the jarosite-alunite family, and lusungite discredited
Authors: Pring A. , Birch W. D. , Dawe J. , Taylor M. , Deliens M. , Walenta K. 
Published: December 2006

AbstractKintoreite is a new lead iron phosphate mineral in the alunite-jarosite family, from Broken Hill, New South Wales, Australia. It is the phosphate analogue of segnitite and the iron analogue of plumbogummite. Kintoreite occurs as clusters and coatings of cream to yellowish green rhombohedral crystals up to 2 mm high and with the principal form {112}. The mineral also forms waxy, yellowish green globular crusts and hemispheres on other phosphate minerals. These associated species include pyromorphite, libethenite, rockbridgeite/dufrenite, apatite and goethite. Kintoreite formed during oxidation of primary ore rich in galena, in the presence of solutions with high P/(As + S) ratios. The mineral is named for the locality, the Kintore opencut, in which it is most common. A mineral closely resembling kintoreite in composition has also been found at several mines in Germany. Type material is preserved in the Museum of Victoria and the South Australian Museum.Electron microprobe analysis showed a nearly complete spread of compositions across the P-dominant portion of the segnitite-kintoreite series. The selected type specimen has an empirical formula of Pb0.97(Fe2.95Zn0.13Cu0.02)Σ3.10[(PO4)1.30(AsO4)0.39(SO4)0.18(CO3)0.11]Σ1.98(OH)5.45·0.74H2O, calculated on the basis of 14 oxygens and with all Fe trivalent. The simplified formula is PbFe3(PO4)2(OH,H2O)6. Kintoreite crystals are translucent with a vitreous to adamantine lustre, with globules appearing waxy. The streak is pale yellowish green and the Mohs hardness is ∼ 4. Crystals show good cleavage on {001} and are brittle with a rough fracture. The calculated density is 4.34 g cm−3. Kintoreite crystals are uniaxial negative with RIs between 1.935 and 1.955 and show light yellowish green to medium yellow pleochroism.The strongest lines in the X-ray powder pattern are (dobs, Iobs, hkl) 3.07(100) 113; 5.96(90)101; 3.67(60)110; 2.538(50)024; 2.257(50)107; 1.979(50)303; 1.831(40)220. The X-ray data were indexed on a hexagonal unit cell by analogy with beudantite, giving a = 7.325(1) Å, c = 16.900(3) Å, V = 785.3(5) Å3 and Z = 3. The probable space group is Rm, by analogy with beudantite and other members of the alunite-jarosite family. Powder X-ray diffraction data for several intermediate members suggest that the segnitite-kintoreite series may not represent ideal solid solution.During the study of kintoreite, part of the type specimen of lusungite from Zaïre was obtained and shown to be goyazite. The IMA's Commission on New Minerals and Mineral Names has voted to discredit lusungite as a species, and has approved the renaming of the ‘lusungite’ group as the segnitite group. However, as relationships between crystal structure, order-disorder and solid solution in the Pb-rich minerals of the alunite-jarosite family are not well documented, the nomenclatural changes resulting from this study should be seen as interim only.
The crystal structure of vlodavetsite, AlCa2(SO4)2F2Cl·4H2O
Authors: Starova G. L. , Filatov S. K. , Matusevich G. L. , Fundamensky V. S. 
Published: December 2006

AbsractThe crystal structure of vlodavetsite, AlCa2(SO4)2F2Cl·4H2O, has been determined, space group I4/m, a = 6.870(1), c = 13.342(2) Å, Z = 2, Dx = 2.35 g/cm3. The polyhedron cation chains are parallel to [001] and consist of couples of distorted Ca octahedra alternating with one distorted Al octahedron rotated through 24° with respect to the former. The chains are linked by SO4-tetrahedra so that all of the four tetrahedron oxygen atoms take part in coordination of Ca atoms to form a distorted octahedron with Cl and F atoms. The Al coordination polyhedron consists of two F atoms and four oxygen atoms belonging to water molecules. There is a specific interaction via hydrogen bonds between oxygen atoms of SO4-tetrahedra and water molecules.
Picrite sills and crystal-melt reactions in the Honningsvåg Intrusive Suite, northern Norway
Authors: Tegner Christian , Robins Brian 
Published: December 2006

AbstractField relations in the upper part of Intrusion II of the Caledonian Honningsvåg Intrusive Suite show that some peridotite sheets transgress, and include in situ rafts of, the adjacent gabbroic cumulates. Modal and textural analyses of three olivine melagabbro sheets show non-cotectic mineral proportions that are likely to result from crystal-melt reactions. Discordant, replacive fingers and pipes of feldspathic peridotite along interfaces between peridotite and overlying olivine melagabbro also suggest crystal-melt reactions.It is proposed that several picritic sills intruded porous gabbroic cumulates in the upper part of Intrusion II. Lateral infiltration of picritic magma led to crystal-melt reactions, mainly assimilation of plagioclase and precipitation of olivine, resulting in the formation of olivine melagabbro and peridotite sheets, and replacive fingers and pipes of feldspathic peridotite.
The production of chemically stratified and adcumulate plutonic igneous rocks
Authors: Tait Stephen R. , Jaupart Claude 
Published: December 2006

AbstractWe review recent advances on the physical principles of crystallization in multicomponent systems, and use them to provide a framework for interpreting petrological and geochemical observations from igneous intrusions. The thermal structure of crystallizing boundary layers imposes strong constraints on the chemical and mineralogical compositions of the solid that can form from a given melt. The thermal problem is largely independent of the chemical composition of the melt, and sets the course of crystallization. A key problem to understand is the temperature of the solidification front (which we take to mean that point at which the last drop of liquid solidifies) particularly in the geologically relevant case in which the temperature at the cold boundary is below the eutectic temperature. Focussing on the solidification front rather than on the liquidus is a valuable perspective. Adcumulus growth requires specific conditions and much can be learned from trying to understand how these can develop from given starting conditions. We discuss the physical reasons and field evidence for the existence of mushy layers, where solid fraction and temperature vary by large amounts. In such regions of the magma chamber, thermodynamic equilibrium is nearly achieved locally and, for a given temperature, this specifies the composition of the interstitial melt. Thus, in a magma chamber, the whole liquid line of descent is present simultaneously. Compositional convection is likely to set in, and this exchange between the interior of the mushy layer and the main reservoir leads to a chemically stratified solid, and to adcumulus growth. The contribution of crystal settling to the floor cumulates is evaluated as a function of the magnitude of convective heat flux through the roof. It is shown that crystal settling is unlikely to overwhelm in-situ nucleation and growth at the floor.
Melt movement and the occlusion of porosity in crystallizing granitic systems
Authors: Bryon D. N. , Atherton M. P. , Cheadle M. J. , Hunter R. H. 
Published: December 2006

AbstractPorosity occlusion has been studied in a granodiorite rock from the Peruvian Coastal Batholith. The texture of the granodiorite is characteristic of Cordilleran I-type rocks, and the textural relations and modelled crystallization path within the quaternary An-Ab-Or-Qz system indicate alkali feldspar was the last major phase to start crystallizing. In thin section, alkali feldspar crystals occur both as large anhedral ‘plates’ containing numerous inclusions, and small interstitial cuneiform ‘pockets’. The alkali feldspar pockets are interpreted as late stage nucleation and growth of new crystals in pores that became isolated from the larger crystals during the latter stages of crystallization. Their geometry therefore mirrors that of the pores immediately after isolation.From the modal abundance of the interstitial pockets, and taking into account contemporaneous growth of the other major phases, it is suggested that crystallization in isolated pores involved solidification of the final 3–4% of liquid. Alkali feldspar growth on the rims of the large anhedral plates prior to pore isolation is evidence for the localised (mm-cm scale) diffusion of chemical species within the interconnected melt phase. However, Rayleigh number calculations indicate that the separation of melt from crystals by compositional convection is unlikely to have occurred during interstitial crystallization.