bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structural behaviour of the nepheline family: (1) Sr and Ba aluminates (MAl2O4)
Authors: Henderson C. M. B. , Taylor D. 
Published: December 2006

AbstractThe structural relations of solid solutions in the series (Sr1−xBax)Al2O4 were studied using room- and high-temperature X-ray methods, infra-red spectroscopy, and DTA. At room temperature, SrAl2O4 and solid solutions with x up to 0.31 are monoclinic, between x = 0.31 and 0.43 monoclinic and hexagonal forms coexist, and between x = 0.43 and 1.0 only hexagonal forms occur. On heating, a member of the monoclinic series of solid solutions transforms to hexagonal symmetry over a range of temperature within which both monoclinic and hexagonal forms coexist. The proportion of the hexagonal form increases instantaneously as the temperature is raised. The transformation temperature decreases with increasing BaAl2O4 in solid solution and, in addition, the temperature width of the region of coexistence is markedly enlarged. SrAl2O4 transforms over the range 665–705 °C and (Sr0.7Ba0.3)Al2O4 over 170–405 °C. The DTA trace for SrAl2O4 shows a peak at 677 °C. On cooling, the transformations show hysteresis of 15 to 25 °C.The coexisting monoclinic and hexagonal forms are believed to be isochemical, and discontinuities in cell parameters occur within the region of coexistence both in the compositional series at room temperature and in the elevated temperature transformation experiments. The low-to-high transformation is accompanied by a volume change of −0.2 to −0.3 %, and is believed to be first-order displacive with additional characteristics similar to those of martensitic transformations.The thermal expansion behaviour of structures in the (Sr,Ba)Al2O4, series indicates that two tilt systems are operative: co-operative rotation of tetrahedra about the c-axis, and tilting of tetrahedra relative to the 0001 plane.The results for the (Sr,Ba)Al2O4 series are shown to be invaluable in reinterpreting the structural behaviour of members of the nepheline and leucite groups of minerals.
Chemical and morphological variation in tourmalines from the Hub Kapong batholith of peninsular Thailand
Authors: Manning D. A. C. 
Published: December 2006

AbstractElectron probe microanalysis of tourmaline from late-stage aplites and mineralized (Sn-W) pegmatites from the Hub Kapong batholith of peninsular Thailand has revealed considerable chemical variation, and has shown that skeletal tourmaline crystals predominate within the pegmatites. The tourmalines show substitution towards the schorl end-member of the schorl-dravite series, as well as substitution towards alkali-free or proton deficient tourmaline. The extent of both substitutions increases (a) from aplites to pegmatites and (b) from core to rim within a single grain and so is believed to become greater with increasing degrees of differentiation of the aplite-pegmatite system. The development of skeletal crystals within the pegmatites and non-skeletal crystals within the aplites is believed to be due to the different kinetics of crystal growth obtaining within a hydrous, pegmatitic, fluid (viz. heterogeneous nucleation and comparatively rapid crystal growth rates) which in turn arise from differences in the structure of the aplitic magma and pegmatitic fluid. The observed chemical and morphological variation shown by the tourmalines is used to discuss the petrogenesis of the aplites and pegmatites, and associated ore deposits. During differentiation, the volatile content of the aplite magmas increased, leading to water saturation and the separation of a hydrous pegmatitic fluid. After a period of coexistence, possibly in chemical equilibrium, the crystallization of the pegmatites continued once the aplite magma had completely consolidated.
Astrophyllite from Kangerdlugssuaq, East Greenland
Authors: Layne Graham D. , Rucklidge John C. , Kent Brooks C. 
Published: December 2006

AbstractAstrophyllite has been found in alkalic pegmatite dykes on the two sides of Kangerdlugssuaq fjord. At the eastern locality, Kraemers Island, the dyke is silica oversaturated and the astrophyllite occurs in a broad tabular crystal habit. The dyke at the western locality, Bagnaesset, is silica undersaturated and the astrophyllite occurs in elongated prisms of acicular habit. Electron probe analyses of the crystals of the two habits have shown systematic chemical differences which not only relate to Mn and Ti compositional variations, but also reveal departures from ideal stoichiometry in varying degrees. Based on this latter feature a model involving polysomatism has been constructed which may explain the differences in crystal habit.
The structural relation between svetlozarite and dachiardite
Authors: Gellens L. R. , Price G. D. , Smith J. V. 
Published: December 2006

AbstractSvetlozarite, previously described as a new member of the mordenite group of zeolites, is reinterpreted as a multiply twinned and highly faulted dachiardite. X-ray diffraction study and transmission electron microscopy revealed (001) twins and (100) stacking faults. The former are attributed at least mainly to the insertion of a b glide plane between dachiardite sheets at each twin interface, which preserves the 5-ring linkages between the sheets. The latter are associated with loss of the C face-centring relation, and are attributed to replacement of shared 5-rings by linked 4-rings in the dachiardite sheets. Further study is needed to determine whether the structural faults in the dachiardite structures are chemically controlled.
Stanleyite, a new vanadium sulphate mineral from Peru
Authors: Livingstone A. 
Published: December 2006

AbstractStanleyite, a cobalt-blue mineral, occurs as efflorescent outgrowths on patronite from Cerro de Pasco, Minasragra, Peru. The determined composition is very close to the ideal formula VOSO4.6H2O and yields an empirical formula of V1.01O1.01S0.99O3.99 5.78H2O on the basis of O = 5 in the anhydrous part. X-ray powder data (31 lines) indexed on an orthorhombic cell give a 12.12, b 9.71, and c 14.92Å, cell volume 1755.8Å3 and Z = 8. Refractive indices are α 1.505, β 1.519, and γ 1.533, D is 1.95 (measured) and 2.01 (calculated), H = 1−1½ (Mohs). Thermal analysis and X-ray powder data show stanleyite to be quite different from minasragrite (the pentahydrate) which it clearly mimics. Associated minerals are potassium alum, pyrite, and quartz.
Oxygen diffusion studies. I. A preliminary ion microprobe investigation of oxygen diffusion in some rock-forming minerals
Authors: Freer R. , Dennis P. F. 
Published: December 2006

AbstractThe self diffusion of oxygen has been studied in prepared natural crystals of albite, grossular garnet, quartz, and ruffle by isotope exchange with hydrothermal water enriched in 18O, and subsequent analysis by ion microprobe. Measured oxygen diffusion coefficients (D) in quartz (‖c) may be described by D = 1.08 × 10−11 exp(−31.5 kcal/RT) cm2s−1 at 600−750°C and 1 kbar water pressure. For grossular, D = 2.5 × 10−16 cm2s−1 at 1050°C and 8 kbar, and D = 4.8 × 10−17 cm2s−1 at 850 °C and 2 kbar. All ruffle crystals exhibited variable amounts of corrosion, and an approximate diffusion coefficient of D(‖c) = 3.16 × 10−15 cm2s−1 cm2s−1 was obtained at 1050 °C and 1 kbar. Oxygen diffusion coefficients in albite, perpendicular to (001) faces, have been determined as a function of pressure at 600 °C Between 0.5 and 8.0 kbar pressure no systematic variation in the results was observed and most of the data may be described by D = 4.1 (±0.5) × 10−15 cm2s−1. Slow oxygen diffusion rates in quartz and garnet suggest that these minerals should have high ‘closure temperatures’ for oxygen exchange, and may provide reliable oxygen isotope exchange geothermometers.
Origin of some of the Rhum harrisite by segregation of intercumulus liquid
Authors: Donaldson Colin H. 
Published: December 2006

AbstractNew field observations of certain harrisite occurrences are presented, including: interruption of layers; splitting of very thick layers into several smaller ones; existence of small isolated lenses and pods of harrisite and of upwardly extending tongues of harrisite; harrisite forming parts of the matrix of breccias; and isolated pods of harrisite along the western margin of the intrusion. These layers, lenses, tongues, and pods seem to have crystallized within the cumulus mush rather than at the mush magma boundary. It is proposed that the rock in these instances represents segregated, intercumulus melt which ‘ponded’ beneath relatively impermeable layers in the cumulus mush. Several ways in which supercooling may have arisen to cause skeletal olivine growth are considered and previous estimates are thought to need reduction by 10–20°C. It is suggested that segregation of upward-filtering melt in other layered intrusions might produce layers indistinguishable from ‘uniform’ cumulate.
The role of fractional crystallization in the formation of granitic and intermediate rocks of the Beinn Chaisgidle Centre, Mull, Scotland
Authors: Walsh J. N. , Clarke E. 
Published: December 2006

AbstractMajor and trace element data are presented for the basic, intermediate, and acid rocks of the Beinn Chaisgidle Centre of the Tertiary igneous complex on the Isle of Mull. The variation in the bulk chemical composition, the iron enrichment trend in the clinopyroxenes, the systematic decrease in concentrations of the transition metal cations, and the increase in the incompatible elements suggest that the magma from which these rocks formed underwent crystal fractionation. The rocks show a coherence of rare earth element patterns for all the rocks in the sequence, and there is a progressive increase in negative Eu anomaly with increasing silica content.
Water-undersaturated melting experiments bearing upon the origin of potassium-rich magmas
Authors: Barton Michael , Hamilton D. L. 
Published: December 2006

AbstractThe water-undersaturated melting relationships of an orendite (with 1.23% H2O as shown by chemical analysis) from the Leucite Hills, Wyoming, have been determined at pressures up to 30 kbar. The dominant liquidus and near-liquidus phases are leucite, olivine, orthopyroxene, clinopyroxene, and garnet. Leucite is stable only at pressures below 5 kbar, but at 27 kbar, minor olivine, orthopyroxene, clinopyroxene, and garnet crystallize simultaneously at or near the liquidus. The following reaction relationships occur with falling temperature in the orendite magma: (a) a reaction between olivine and melt to yield orthopyroxene at pressures above 12 kbar; (b) a reaction between olivine and melt to yield phlogopite at pressures below 12 kbar; (c) a reaction between olivine, orthopyroxene and melt to yield phlogopite and probably clinopyroxene at pressures above 12 kbar; (d) a reaction between leucite and melt to yield sanidine at pressures below 5 kbar. Electron microprobe analyses demonstrate that the ortho- and clinopyroxenes crystallized from orendite are aluminium-poor; the clinopyroxenes contain insufficient aluminium to balance sodium and titanium (Al < Na+2Ti) and these elements must either be partly balanced by (undetermined) chromium or ferric iron or be involved in substitutions which do not require trivalent ions for charge balance. The experimental results indicate that relatively silica-rich potassic magmas such as orendite form under water-undersaturated (essentially carbon dioxide free) conditions at pressures of about 27 kbar by small degrees of melting of phlogopite-garnet-lherzolite or by larger degrees of melting of peridotite which has been enriched in potassium and incompatible elements. The peralkalinity of some potassic magmas (such as orendite and wyomingite) could reflect a primary geochemical characteristic of the source rock, but could also result from the melting of phlogopite in the presence of residual pyroxenes. The association of silica-poor, mafic madupites and relatively silica-rich orendites and wyomingites in the Leucite Hills can be explained in terms of the relative effects of water and carbon dioxide on melting processes within the upper mantle.
A discussion of carbonatite evolution and nomenclature, and the generation of sodic and potassic fenites
Authors: Woolley A. R. 
Published: December 2006

AbstractPossible evolutionary paths of alkali-rich carbonatite magma may be related to the production of sodic and potassic fenites. It is concluded that the latter are generated not from separate Na- and K-rich carbonatites, but by the earlier preferential loss of Na from a sodi-potassic carbonatite magma. Trends of both Fe and Mg enrichment in carbonatites are illustrated from a number of centres, and ascribed to crystal fractionation, although metasomatism may be partly responsible. Current nomenclature of carbonatites is unsatisfactory and a division into sövites, magnesiocarbonatites and ferrocarbonatites is proposed, based on rock chemistry.
Phase diagrams: the composition of the material being instantaneously abstracted from the liquid during equilibrium crystallization in binary systems with solid solution between the end members
Authors: Taylor D. 
Published: December 2006

AbstractA method is presented for determining the composition of the material being instantaneously abstracted from the liquid during equilibrium crystallization of a solid solution in a binary system. It shows that, except when the solidus and liquidus curves are straight and parallel, the composition of the material being instantaneously abstracted from the liquid does not lie on the straight line joining the composition of the first crystals and last liquid for that bulk composition. Despite this, the latter straight line is a reasonable approximation to the actual curve.
Supercooling and the crystallization of plagioclase, olivine, and clinopyroxene from basaltic magmas
Authors: Corrigan G. M. 
Published: December 2006

AbstractEffects of supercooling have been studied in a range of basaltic melts by isothermal and constant cooling rate experiments at one-atmosphere, using the wire-loop container method. The nucleation of plagioclase in these melts is systematically controlled by supercooling (-ΔT), time below the liquidus temperature, and initial superheating (+ΔT). The temperature at which the melt is initially superheated prior to supercooling controls the temperature at which crystal nucleation first takes place in a supercooled melt undergoing cooling; the greater the + ΔT the larger the degree of supercooling required prior to nucleation of the liquidus phase during cooling. In all six compositions investigated there are at least two fields in time-temperature space, one in which the liquidus phase always fails to nucleate on supercooling (favoured by small -ΔT) and one (favoured by large -ΔT) in which it always nucleates. These two fields may be separated by another in which the liquidus phase may or may not crystallize. Supercooling phenomena are not restricted to the liquidus phase but can also occur when the melt becomes saturated with subsequent phases. It is shown that the composition of plagioclase varies systematically with -ΔT and it is demonstrated that isothermal supercooling ‘lines’ can be used with a relatively high degree of accuracy to predict when nucleation of the liquidus phase will take place during constant cooling rate experiments.
Theisite, a new mineral from Colorado
Authors: Williams S. A. 
Published: December 2006

AbstractFound by N. Theis at a uranium prospect near Durango, Colorado. Occurs with uraninite, galena, malachite, azurite, etc. Colour pale blue-green, H = 1½, G = 4.25. Optically 2Vα ≈ 0°, α = 1.755, β = γ = 1.785; non-pleochroic. Chemical analysis on 1034 µg gave CuO 33.3 %, ZnO 33.1, CaO 0.3, As2O5 14.8, Sb2O5 7.0, H2O 10.5 leading to Cu5Zn5{(As,Sb)O4}2(OH)14. The cell indexes as orthorhombic a = 8.225Å, b = 7.123, c = 14.97. Strongest lines are 14.97 (9), 7.483 (5), 4.112 (4), 3.741 (10), 2.996 (4), 2.534 (9), 1.830 (5), 1.553 (3). The mineral and name have been approved by the Commission on New Minerals and Mineral Names, IMA.
The retrogression of ultramafic granulites from the Scourian of NW Scotland
Authors: Sills Jane D. 
Published: December 2006

AbstractScourian ultramafic granulites from the Assynt region, of Sutherland were retrogressed to amphibolite facies during the Inverian and in Laxfordian shear zones. Inverian assemblages are dominantly chlorite and tremolite with minor anthophyllite and dolomite. Laxfordian assemblages are cummingtonite, chlorite, and dolomite with only minor amounts of tremolite. Retrogression took place on a falling temperature path with temperatures between 750 and 550°C, and with H2O forming more than 90% of the fluid phase. Initially retrogression was caused by the influx of large volumes of hydrous fluid associated with the development of Inverian folds. During the Laxfordian shearing PCO2 was increased slightly. Serpentinization of olivine occurred at a much later stage.
Barium silicates in stratabound Ba-Zn mineralization in the Scottish Dalradian
Authors: Fortey N. J. , Beddoe-Stephens B. 
Published: December 2006

AbstractBarium feldspar and barian muscovite are major constituents of the Aberfeldy Ba-Zn mineralization. Celsian varies from equigranular to a platy habit in quartz-celsian rock and forms porphyroblasts in schist and marble. Hyalophane is less common. Barian muscovite is a major component of the schist in the mineralized zone. Celsian (> 80 % Cn) and/or hyalophane coexist with muscovite containing c.6% Ba, and c.8.5% Ba was measured in muscovite from one feldspar-free specimen. Cymrite separated from foliated quartz-celsian rock conformed to the formula BaAl2Si2O8·H2O. The rock textures reflect regional metamorphism, but it is believed that the barium silicates are ultimately authigenic in origin. The platy habit of much of the celsian may have been inherited from cymrite formed during the development of tectonic fabrics.
Morphology and alteration of asbestiform grunerite and anthophyllite
Authors: Cressey B. A. , Whittaker E. J. W. , Hutchison J. L. 
Published: December 2006

AbstractSections perpendicular to [001] of ion-thinned specimens of amosite (fibrous grunerite) from Penge, Transvaal and anthophyllite from Paakila, Finland and Söndeled, Norway, have been examined by high-resolution transmission electron microscopy. Observations on the nature of grain boundaries and alteration are compared with those of other workers on other fibrous amphiboles. Fibrous crystals grow with their fibre (c) axes approximately parallel to one another but they have considerable rotational disorder about that axis. Grain boundaries are generally irregular in shape and only follow low-index planes for short sections. In all specimens the amphibole has undergone some alteration to sheet silicates along grain boundaries, fractures, cleavages, and multiple-chain lamellae. Anthophyllite alteration products are talc, serpentine and chlorite, and amosite alteration products approximate to iron analogues of talc and serpentine. Talc layers are generally planar and their orientation is strongly controlled by the amphibole structure, whereas serpentine and chlorite layers often curve and their orientations are less frequently related to that of the amphibole. Comparison of specimens which appear finely fibrous in hand specimen with those which appear coarser, acicular or massive suggests that the nature of fibres produced by crushing is mainly controlled by the grain boundaries in the former type, but other factors such as fractures, cleavages, and defects are more important for the latter types.
Genesis of tourmalinites from Belgium: petrographical and chemical evidence
Authors: Fieremans M. , De Paepe P. 
Published: December 2006

AbstractThe petrographical and chemical characteristics of the tourmalinite pebbles from the Lower Devonian conglomerates of Belgium are presented together with selected trace element data. The tourmalinites are shown to represent metasomatically altered rocks of variable origin and composition. A model of subvolcanic hydrothermal alteration is proposed.
The mineral chemistry of dolerites and gabbros from the central Complex of Slieve Gullion, NE Ireland
Authors: Gamble John A. 
Published: December 2006

SynopsisThe dolerites and gabbros of the Tertiary central complex of Slieve Gullion, NE Ireland, represent a suite of tholeiitic magmas (varying from tholeiitic basalt to tholeiitic andesite, Gamble 1979a) which crystallized in the root-zone of a shield volcano. The ubiquity of biotite suggests that the magmas were hydrous and, in addition, both silicate (olivine) and oxide (Ti-magnetite) phases show evidence for oxidation at high temperatures.
The determination of ferrous and ferric iron in rocks and minerals; and a note on sulphosalicylic acid as a reagent for Fe and Ti
Authors: Hey M. H. 
Published: December 2006

SynopsisInstrumental methods of chemical analysis, including electron and ion-probes, X-ray fluorescence, atomic absorption, and plasma-source spectrometry, have largely replaced classical wet-chemical analysis except for ‘referee’ analyses, but have not so far proved able to determine the net state of oxidation of a rock or mineral with reasonable accuracy. Mössbauer spectroscopy can indeed give fairly accurate Fe2+and Fe3+estimates in favourable circumstances, but fails when the Fe2+: Fe3+ratio is very small or very large or when the iron is present in several different lattice positions with different surroundings; and it cannot arrive at the net state of oxidation when other elements of variable valency are present. The term ‘net state of oxidation’ calls for some comment, and is dealt with in the full paper; for the moment we note as an example that Mössbauer spectroscopy shows that much of the iron in ludlockite is ferric, whereas a ‘ferrous iron’ determination corresponds to an arsenate of lead and ferrous iron, from which it follows that part of the arsenic must be trivalent, a result that could not have been arrived at from either the ‘ferrous iron’ or the Mössbauer data along. Thus in the present state of the art a wet-chemical method for net state of oxidation is a necessity.
Childrenite in South-West England
Authors: Braithwaite R. S. W. , Cooper B. V. 
Published: December 2006

SynopsisChildrenite (Fe,Mn)AlPO4,(OH)2.2H2O, the iron-rich end-member of the childrenite-eosphorite diadochic series, was first discovered by Brooke (1823) on specimens from near Tavistock in Devon. Subsequently it has been recorded from a small number of other British localities, mostly in the Tavistock area, and also from near St. Austell in Cornwall, and from one locality in Cumbria. The Sir Arthur Russell collection, now in the British Museum (Nat. Hist.), has specimens from a few additional localities, all near Tavistock, and the Geological Museum, Institute of Geological Sciences, has a specimen from Wheal Jane, near Truro.