bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical distinction between igneous and metamorphic orthopyroxenes especially those coexisting with Ca-rich clinopyroxenes: a re-evaluation
Authors: Rietmeijer Frans J. M. 
Published: December 2006

AbstractA previously suggested simple relationship in a diagram of(Al2O3vs. MgO + FeO + Fe2O3)opx for the distinction between igneous and metamorphic orthopyroxenes is shown to be inadequate. A revised diagram is presented and its limitations are discussed. A diagram showing Fe2+/(Fe2+ + Mg) vs. 100Ca/(Fe2+ + Mg + Ca) for orthopyroxenes coexisting with Ca-rich clinopyroxenes proves to be useful for the discrimination of igneous and metamorphic orthopyroxenes and for evaluation of the extent and physical conditions of regional orthopyroxene re-equilibration.
Equilibria in the Mg-rich part of the pyroxene quadrilateral
Authors: Jenner G. A. , Green D. H. 
Published: December 2006

AbstractPyroxene phase relations in the Mg-rich corner of the pyroxene quadrilateral, at 1 atmosphere, have been reinvestigated. Experimental studies on sixteen selected compositions in the systems CMS and CFMS were undertaken in the temperature range 1100–1400 °C. The results of this study clarify our understanding of the pyroxene stability relations at low pressure. In particular, the demonstration that there is a high-temperature stability field of orthoenstatite denies the existence of a stable (or real) invariant point defined by the reactions OE = PE + DI, PE + DI = PI, and OE + DI = PI, in the system CaMgSi2O6-Mg2Si2O6. New phase relations, consistent with the experimental findings of this and other studies, for the Mg-rich corner of the pyroxene quadrilateral are presented. These new phase relations may be of use in interpreting the origin of volcanic rocks containing magnesian pigeonite.
Crystallization of plagioclase, augite, and olivine in synthetic systems and in tholeiites
Authors: Biggar G. M. 
Published: December 2006

AbstractExperimental data from the system CaO-MgO-Na2O-Al2O3-SiO2 and from the system CaO-MgO-FeO-Al2O3-SiO2 are used to show the nature of the changes in composition, with temperature and with pressure, of liquids in equilibrium with augite, plagioclase, and olivine as MgO in the system CaO-MgO-Al2O3-SiO2 is partially replaced by FeO and as Na2O replaces CaO. As differentiation of tholeiitic basalts proceeds, Fe/Mg increases, Na/Ca increases, and normative hypersthene increases and these effects alter the solubilities, and hence the proportions of augite, plagioclase, and olivine which co-precipitate. In particular olivine becomes more soluble (less is precipitated) as Fe/Mg increases; plagioclase becomes more soluble but augite less soluble as Na/(Na + Ca) increases; augite also becomes less soluble as normative hypersthene increases, and as pressure is reduced during ascent.Experimental data from remelted ocean tholeiites encounter the same equilibrium and are presented and compared with the data from synthetic systems.Some natural examples of daughter liquids related to parents by crystallization of augite, plagioclase, olivine, are combined with the experimental data and with some model calculations to demonstrate that only a very limited range of proportions of augite : plagioclase: olivine (approximately 30 : 50 : 15 to 20 : 60: 20) produces daughter liquids which lie on the major element variation of the tholeiitic basalt series. Other proportions lead to daughter liquids which are not basalts. In the light of these restrictions, several recent publications are reinterpreted as examples of fractionation of augite, plagioclase, and olivine, rather than examples of partial melting. The recognition of the small effect that massive (50 to 83%) crystallization has on basaltic chemistry by contrast with the large effect that small accumulations of phenocrysts can have is particularly emphasized in this reinterpretation.Comparisons and possible relationships are suggested between some low-K2O, low-TiO2 tholeiites; some calcic-, aphyric-, dykes of some tholeiitic provinces; some chilled margins of some layered intrusions; some basalts from Iceland, and some basalts from the ocean ridges.
Crystal-chemical characterization of NaAlSiO4 with the CaFe2O4 structure
Authors: Yamada Hirohisa , Matsui Yoshito , Ito Eiji 
Published: December 2006

AbstractA high-pressure modification of NaAlSiO4, with the calcium ferrite structure was synthesized at pressures higher than 24 GPa using a double-stage split-sphere type high-pressure apparatus. The unit cell dimensions are: a=10.1546(8), b=8.6642(8), c= 2.7385(4) Å, and V = 240.93(3) Å3 with the space group Pbnm. Calculated density is 3.916(1) g/cm3. The crystal structure was determined by the ordinary powder X-ray method. Both M1O6 and M2O6 octahedra run parallel to the c-axis, forming edge-shared double chains. The shared edges exhibit remarkable shortening (2.25–2.39 Å). Sodium atoms are located in the ‘tunnel’ formed by the linked double chains, being in eightfold co-ordination. The structure is very similar to that predicted by Dempsey and Strens (1976) with the aid of the DLS method. The possible instability of the calcium ferrite type of Mg2SiO4 is discussed.
Geochemistry and mineralogy of Triassic sandstones and implications for groundwater composition
Authors: Spears D. A. 
Published: December 2006

AbstractBorehole samples from the Wildmoor Sandstone Formation have been analysed for whole-rock major and trace elements and the mineralogy determined by X-ray diffraction and conventional thin sections. The forty-two samples studied were obtained from boreholes drilled in a long established effluent site and from control boreholes away from the site. Elements are associated with one or more of calcite, quartz, K-feldspar, and clay plus oxide. The most important mineralogical change due to current infiltration is progressive loss of calcite. Background element concentrations are established and only Pb, and in one sample Cu and Zn, are found in higher concentrations representing anthropogenic additions to the system.
The dependence of alumina and silica contents on the extent of alteration of weathered ilmenites from Western Australia
Authors: Frost M. T. , Grey I. E. , Harrowfield I. R. , Mason K. 
Published: December 2006

AbstractThe distribution of the minor impurities, aluminium and silicon, between co-existing phases in altered ilmenite grains from three Western Australian localities has been investigated using SEM and electronmicroprobe analyses. A striking dependence of the impurity levels on the Ti/(Ti + Fe) fraction is observed. For compositions with Ti/(Ti + Fe) between 0.45 and 0.60, i.e. between ferrian-ilmenite and pseudorutile, the impurity content is virtually independent of Ti/(Ti + Fe), and is very low (0.2 wt. % Al2O3. 0.05 wt. % SiO2). For compositions between those of rutile and pseudorutile, there is a direct correlation between the impurity contents and the Ti content of the alteration phase. The impurity levels increase with increasing Ti/(Ti+Fe) to about 3 wt. % Al2O3and 1 wt. % SiO2for compositions close to TiO2. Thus during the latter stages of ilmenite alteration, alumina and silica are extracted from the ambient environment and are coprecipitated with, or adsorbed on to, the alteration products. The observed dependence of the alumina and silica contents on extent of alteration is consistent with a two-stage alteration mechanism earlier proposed (Grey and Reid, 1975).
A Mössbauer study of some Australian iron ore minerals
Authors: Fysh S. A. , Ostwald J. 
Published: December 2006

AbstractSix specimens of Australian iron ore, three hematite-rich and three goethite-rich, have been investigated by Mössbauer spectroscopy at both 300 K and 4.2 K. The resulting spectra provide data relevant to crystallite particle size variations in the hematite and goethite, the extent of isomorphous replacement, and the existence within one specimen of a poorly defined goethite-like material.
Synthesis, properties, and dehydroxylation of members of the crandallite-goyazite series
Authors: Gilkes R. J. , Palmer B. 
Published: December 2006

AbstractUnit-cell parameters of synthesized members of the crandallite (a = 7.007 Å, c = 16.216 Å)-goyazite (a = 7.013 Å, c = 16.650 Å) series vary linearly with composition between end-members. Most members of the series consist of 0.1 μm platy crystals, but crandallite also contains some larger (1–5 µm) tapered crystals elongated along the c axis.With increasing Sr substitution the dehydroxylation temperature decreases from c. 475 °C for crandallite to 420 °C at 20 mole % Sr, and then increases to 440 °C for goyazite. Partial dehydroxylation of crandallite is accompanied by contraction of the c unit cell parameter and expansion of a, thereby retaining an unaltered unit cell volume. The much greater sensitivity of c to both Sr substitution and dehydroxylation may be due to the rigidity of continuous sheets of Al(OH)4O2 octahedra which are parallel to the (001) plane in these minerals.
Iron-rich talc-opal-minnesotaite spherulites and crystallochemical relations of talc and minnesotaite
Authors: Kager P. C. A. , Oen I. S. 
Published: December 2006

AbstractZoned spherulites in greenalite-siderite-silica rocks of the Emilia-San Valentin lead-zinc deposit, Sierra de Cartagena, SE Spain, show a core of iron-rich talc, (Mgl.8Fel.2)Si4Ol0(OH)2, an intermediate zone of opal-chalcedony, and a rim of minnesotaite, (Fe2.7Mg0.3)Si4Ol0(OH)2. Crystalllization of the spherulites, presumably from undercooled silica sols carrying dissolved Mg and Fe, began with the non-equilibrium precipitation of metastable iron-rich talc; the residual fluids enveloping the growing spherulites became more iron-rich in composition until metastable equilibrium between iron-rich talc and iron-enriched residual liquid impeded the further growth of the iron-rich talc; the spherulites were then overgrown by colloidal silica flocculates and a rim of minnesotaite precipitated from the iron-enriched residual fluid. The proposed crystallization model implies that, if talc and minnesotaite represent an isomorphic series, under equilibrium conditions there is a broad immiscibility region in the series.
The geochemistry of mafic and ultramafic from the Archaean greenstone belts of Sierra Leone
Authors: Rollinson H. R. 
Published: December 2006

AbstractThe Archaean (c. 2800 Ma) ultramafic rocks in eastern Sierra Leone cut basalt lavas and are mostly olivine-rich cumulates either iron-rich (Fo85–86) and derived from a basaltic or picritic parent, or more magnesian (Fo92–93) derived from an ultramafic melt with c. 18–25 wt. % MgO. In central Sierra Leone the ultramafic rocks are lavas predating tholeiitic basalts.The basalts show a wide variation in Zr/Y, suggesting that garnet was present in the source region of some of these rocks but not others. This implies that melting took place at different depths in the mantle. The REE evidence for basaltic rocks in the upper part of the Nimini belt succession suggests that they were derived from a mantle source region which had already suffered melt extraction. Ti/Zr ratios in the basaltic rocks are also variable and individual belts define different trends on a Ti vs. Zr plot implying that the basaltic rocks evolved in geographically distinct magma chambers. It is likely that the basaltic rocks evolved from a parental liquid with Ti/Zr = 90 via shallow level crystal fractionation. The source region for these rocks therefore had a lower than chondritic Ti/Zr.There are two possible models for the basaltic and ultramafic magmas in the Sierra Leone greenstone belts. First that the ultramafic and basaltic liquids were derived from mantle diapirs of differing size, but originating in the same region of the mantle. Ultramafic liquids were produced in small diapirs, which store large melt fractions, and basaltic liquids in larger diapirs which segregate larger melt fractions. A second model is based upon the double diffusion process suggested for magma chambers at mid-ocean ridges and involves a transient magma chamber from which basalts, derived from parental ultramafic liquids, are erupted, with ultramafic liquids rising directly to the surface when the magma chamber is frozen. The available data does not discriminate between these two models.
Buddingtonite (NH4-feldspar) in the Condor Oilshale Deposit, Queensland, Australia
Authors: Loughnan F. C. , Roberts F. Ivor , Lindner A. W. 
Published: December 2006

AbstractBuddingtonite of similar composition and properties to that described from the type area, is uniformly distributed throughout the upper 600 m of strata in the Condor Oilshale Deposit near Proserpine, Queensland. The mineral, which constitutes up to 16% and averages nearly 10 % of the strata, is associated with abundant montmorillonite, siderite, and quartz as well as minor amounts of disordered kaolinite, illite, calcite, pyrite, cristobalite, and an unnamed species of the jahnsite group. The buddingtonite is concluded to be of diagenetic origin. It developed in an ammonium-rich environment, most probably at significant depth within the mud beneath a stratified lake. Its progenitor, however, remains unknown. The occurrence of this mineral is also of interest in that ammonia could prove an important by-product in the commercial exploitation of the oilshales.
Clinopyroxene solid solutions and water in magmas: results in the system phonolitic tephrite-H2O
Authors: Dolfi D. , Trigila R. 
Published: December 2006

AbstractClinopyroxene solid solutions crystallized at Ptot = 2 kbar in the natural system phonolitic tephrite-H2O (lava type from Etna eruption 1971) indicate a linear increase of ln Xcpxcats with H2Oliq %. After coupling this with the In Xcpxcats pressure dependence found through experiments, a simple relation has been set up for clinopyroxene- and plagioclase-bearing magmas. This relation allows us to calculate the amount of water dissolved in the melt, at any known pressure in the crustal range.
Chemical variation in garnets from aplites and pegmatites, peninsular Thailand
Authors: Manning D. A. C. 
Published: December 2006

AbstractElectron microprobe analyses of almandine-spessartine garnets from pegmatites and aplites from the Hub Kapong batholith and Phuket Island in peninsular Thailand show three types of zoning. Garnets from pegmatites show extreme zoning, with Mn-rich cores (⋍ 80 % spessartine) and Mn-poor rims (⩾ 40 % spessartine), whereas those from aplites are either unzoned (35–40% spessartine) within the limits of detection, or have Mn-enriched rims (cores 45 %, rims 55 % spessartine). The origin of the three types of zoning is considered to reflect different crystal growth histories in each case. The pegmatitic garnets grew under conditions favourable for the development and preservation of marked concentration gradients—low nucleation density, rapid growth rate and slow cation diffusion rates for the crystal and rapid diffusion rates for the pegmatitic liquid. The aplitic garnets had a more complex growth history, with slower growth rates and faster diffusion rates for the crystal, coupled with slower diffusion rates within the aplite magma, tending to prevent the formation and preservation of concentration gradients. Subsequent resorption of aplitic garnets at lower temperatures gave rise to Mn-rich rims because of the preferential retention of Mn by the garnet; lower cation diffusion rates within the crystal permitted these marginal concentration gradients to be preserved.
Chemistry of biotites from a zoned granitic pluton in Morocco
Authors: Mahmood A. 
Published: December 2006

AbstractChemical analyses and structural formulae of biotites from the Zaër pluton, a zoned granitic body in the Central Hercynian Massif of Morocco, are presented. The pluton grades from more mafic single-mica granodioritic facies near the margin to more felsic two-mica granitic facies in the central part. There is a relationship between the composition of the biotites and that of the host rocks. Biotite composition in the internal two-mica facies was influenced by a hydrothermal phase.
Bostwickite, a new calcium manganese silicate hydrate from Franklin, New Jersey
Authors: Dunn Pete J. , Leavens Peter B. 
Published: December 2006

AbstractBostwickite, CaMn63+Si3O16-7H2O, is a new species from the Franklin Mine, Franklin, New Jersey. Chemical analysis yielded MgO 0.9, CaO 5.1, Mn2O3 56.3, Fe2O3 0.5, Al2O3 1.0, As2O5 1.0, SiO2 20.1, H2O [15.1], sum = 100.0%. This yields (Ca0.76Mg0.19)Σ0.95(Mn5.973+Fe0.053+)Σ6.02(Si2.80Al0.16As0.075+)Σ6.02(Si2.80Al0.16AS5+0.07)Σ3.03O16·7.01H2O, corresponding to the idealized formula. The strongest lines in the X-ray powder diffraction pattern are (d, I): 11.3, 100; 3.548, 30; 2.898, 30; 2.567, 40; 2.262, 25; 2.238, 25; 1.470, 25. Bostwickite is dark red in colour; hardness c. 1 (Mohs'); density (meas.)= 2.93 g/cm3. It occurs in radial aggregates of acicular compound crystals. Optically, bostwickite is biaxial negative with 2Vα = 25deg; α = 1.775, Β = 1.798, γ = 1.800;, dispersion strong, r > v; strongly pleochroic with α = β redbrown, γ = yellow-brown; absorption is α = β = γ. Bostwickite is named in honour of Richard C. Bostwick, collector and compiler of data on the minerals of Franklin and Sterling Hill.
Tristramite, a new calcium uranium phosphate of the rhabdophane group
Authors: Atkin D. , Basham I. R. , Bowles J. F. W. 
Published: December 2006

AbstractTristramite, a new mineral of the rhabdophane group, has the composition (Ca0.54U4+0.29Fe3+0.17)Σ1.00 [(PO4)0.79(SO4)0.12(CO3)0.07]Σ0.98·1.77H2O. It occurs as a late-stage replacement or matrix to brecciated uraninite (var. pitchblende) associated with sulphides in hydrothermal veins related to Hercynian granites in south-west England. It is hexagonal, space group P6222, with a 6.913 ± 0.003 Å and c 6.422 ± 0.006 Å. The strongest lines of the indexed powder pattern are 2.99 (100), 2.83 (100), 2.14 (50), 1.850 (50), 5.99 (40), 4.37 (40), 3.46 (30). For comparison, new indexed powder data for rhabdophane from Fowey Consols, Cornwall, are included. The mineral is pale yellow to greenish yellow, uniaxial positive with ω 1.644 and ε 1.664, and does not fluoresce in either short-or long-wave ultraviolet light. The habit is acicular or fibrous and no cleavage has been observed. Density (g/cm3) 3.8–4.2 (meas.), 4.18 (calc.).
Chemical behaviour of sphalerite and arsenopyrite in hydrothermal and metamorphic environments
Authors: Scott S. D. 
Published: December 2006

AbstractExamples of application of equilibria in the systems Fe-Zn-S, Cu-Fe-Zn-S, Fe-As-S, and Fe-Zn-As-S are drawn from modern sulphide-forming hydrothermal vents on the East Pacific Rise, from ancient vein deposits and from metamorphosed sulphide ores. The ZnS content (1.2 and 1.3 mole %) of Cu-Fe-S intermediate solid solution (iss) from the sea-floor deposits gives temperatures of equilibration of 331° and 335 °C from experimental curves, in excellent agreement with the 350 °C expected from actual measurement of the hot springs. Heterogeneities in sphalerite in these deposits do not necessarily represent disequilibrium during deposition but can be explained simply by small fluctuations in aS2. Diagrams of log aS2vs. 1000/T, K for sphalerite and arsenopyrite are useful for estimating temperature and activity of sulphur in hydrothermal or metamorphosed deposits provided that equilibrium can be demonstrated and the systems are properly buffered.The sphalerite geobarometer has had wide applications, some successful (mostly vein deposits) and some not (particularly metamorphosed ores in which chalcopyrite is in contact with sphalerite). Compositions of sphalerites which are totally enclosed within metablastic pyrites represent preserved high P-T equilibria which have been isolated from further reaction during subsequent retrograde conditions by the inert encapsulating pyrite and may provide more reliable estimates of pressure.
Pyrrhotine-pentlandite ore textures: a mechanistic approach
Authors: Kelly D. P. , Vaughan D. J. 
Published: December 2006

AbstractThe kinetics and mechanisms of pentlandite [(Fe,Ni)9S8] exsolution from the monosulphide solid solution [or MSS (Fe,Ni)1−xS] have been studied by synthesis and annealing experiments in part of the Fe-Ni-S system particularly relevant to sulphide nickel orebodies. This experimental work has been combined with the examination of the compositions and textures of pyrrhotine-pentlandite intergrowths from a variety of ore deposits. Isothermal annealing of MSS compositions with varying M:S and Fe:Ni ratios at 400 °C shows the formation of a sequence of textures which depend for their full development chiefly on initial M:S ratio and annealing time. The full sequence of textures starts with heterogeneous nucleation of pentlandite at MSS grain boundaries, the growth of these blebs to form ‘rims’, nucleation of finer bladed particles arranged ‘en échelon’ along fractures, and, finally, homogeneous nucleation of fine orientated pentlandite lamellae. Using the information from the annealing experiments, the inter-growths produced by cooling in the natural ores are interpreted using a simplified Time-Temperature-Transformation Model.
The chemistry, reflectance, and cell size of the erlichmanite (OsS2)-laurite (RuS2) series
Authors: Bowles J. F. W. , Atkin D. , Lambert J. L. M. , Deans T. , Phillips R. 
Published: December 2006

AbstractMicroprobe analyses of members of the erlichmanite-laurite series from Guma Water and Senduma, Sierra Leone and Tanah Laut, Borneo, indicate that complete solid solution is possible between OsS2 and RuS2 with considerable substitution of Os and Ru by Ir, Rh, and Pt. The cell size of the erlichmanite from Guma Water is a = 5.6183±0.0003 Å at a composition (Os0.61Ru0.30Ir0.06Rh0.03)Σ0.93S2 whilst the laurite from Senduma has a composition of (Ru0.88Os0.05Ir0.04 Rh0.03)Σ0.93S2 and a cell size of a = 5.6089±0.0005 Å. Substitution of Os for Ru provides the predominant cause of the variation of cell size. Substitution by other elements of the platinum group appears to produce little effect on cell size and is presumably controlled by genesis rather than considerations of crystal chemistry or structure. The recorded analyses for these elements indicate a pre-dominance of Ir over Rh for members of the series containing more than about 15% of the laurite molecule. For the remainder of the series Rh is more important than Ir. The reflectance in air and oil of the members of the series from Sierra Leone and Borneo are presented and the microhardness of the erlichmanite from Guma Water shown to be 1854 kg/mm2. This is the first report of laurite from Senduma, Sierra Leone.
The Witwatersrand pyrites and metamorphism
Authors: Hallbauer D. K. , Gehlen K. von 
Published: December 2006

AbstractEvidence obtained from morphological and extensive trace element studies, and from the examination of mineral and fluid inclusions in Witwatersrand pyrites, shows three major types of pyrite: (i) detrital pyrite (rounded pyrite crystals transported into the depositional environment); (ii) synsedimentary pyrite (round and rounded aggregates of fine-grained pyrite formed within the depositional environmen); and (iii) authigenic pyrite (newly crystallized and/or recrystallized pyrite formed after deposition). The detrital grains contain mineral inclusions such as biotite, feldspar, apatite, zircon, sphene, and various ore minerals, and fluid inclusions with daughter minerals. Most of the inclusions are incompatible with an origin by sulphidization. Recrystallized authigenic pyrite occurs in large quantities but only in horizons or localities which have been subjected to higher temperatures during the intrusion or extrusion of younger volcanic rocks. Important additional findings are the often substantial amounts of pyrite and small amounts of particles of gold found in Archaean granites (Hallbauer, 1982) as possible source rocks for the Witwatersrand detritus. Large differences in Ag and Hg content between homogeneous single gold grains within a hand specimen indicate a lack of metamorphic homogenization. The influence of metamorphism on the Witwatersrand pyrites can therefore be described as only slight and generally negligible.