bluuebunny/crossref_metadata_2025_split huggingface dataset:
Replacement of OH by OD in layer silicates, and identification of the vibrations of these groups in infra-red spectra
Authors: Russell J. D. , Farmer V. C. , Velde B. 
Published: December 2006

SummaryConditions necessary for exchange between lattice OH groups and D2O in expanding layer silicates are reported. From spectral changes in the 200–1200 cm−1 region resulting from this exchange, in-plane librations of OH co-ordinated to (A1A1), (A1Mg), (A1Fe3+), and (MgMgMg) have been identified in montmorillonite, beidellite, saponite, hectorite, and vermiculite. Both in-plane and out-of-plane librations have been identified for pyrophyllite and celadonite, from comparison of synthetic specimens containing OD with natural or synthetic OH forms. Comparison of hydrogen and deuterium forms of Mg- and Ni-talcs leads to the identification of translational and librational OH vibrations.
A metallographic and microprobe study of the Barranca Blanca meteorite
Authors: Axon H. J. , Faulkner D. 
Published: December 2006

SummaryThe distribution of kamacite, taenite, and plessite suggests that kamacite nucleated at the sulphides, which appear to have been plentifully dispersed in the parent taenite. Such a process could take place without the undercooling that is usually assumed in normal octahedrites. The plessite fields show internal boundaries that are probably relics of grain boundaries in the parent taenitesulphide aggregate. Microprobe investigations have been made of nickel distributions in and between kamacite, taenite, plessite, and schreibersite, and particular attention has been paid to the nickel distribution at the internal grain boundaries in the plessite. Evidence is presented for the diffusion of nickel along these boundaries and for their migration during the later stages of formation of the microstructure.
The metal phase of Horse Creek, Mount Egerton, and Norton County enstatitic meteorites
Authors: Wai C. M. 
Published: December 2006

SummaryResults of an electron microprobe study of the metal phase and perryite inclusions in the metal of Horse Creek, Mount Egerton, and Norton County enstatitic meteorites are given. The origin of the ‘pseudo-octahedral’ structures observed in the metal phase of the Horse Creek and Mount Egerton ‘anomalous enstatitic meteorites’ is discussed.
Genesis of hydrothermal K-feldspar (adularia) in an active geothermal environment at Wairakei, New Zealand
Authors: Steiner A. 
Published: December 2006

SummaryHydrothermal almost pure potassium feldspar (adularia) forms incrustations on fissured wall rocks in an active geothermal environment. Measured max. temperature, 265 °C, and concentration of K+ and Na+ cations in the geothermal fluid require K-feldspar and Na-feldspar to be deposited under equilibrium conditions. On fissure walls only K-feldspar is precipitated, whereas andesine phenocrysts of host rocks are replaced by both K-feldspar and Na-feldspar, and groundmass of host rock is replaced by K-feldspar.Optical data indicate that K-feldspar forming incrustations is partly monoclinic, partly triclinic. The triclinic material displays polysynthetic and ‘microcline’-like twinning, though X-ray diffractograms indicate only monoclinic structure. A primary origin for the triclinic adularia is postulated. Wairakei hydrothermal K-feldspar, max. 0·5 Myr old, is compared with Arkansas adularia 287 or 214 Myr old, also containing both monoclinic and triclinic material. The comparison suggests that, after crystallization, the structural state of adularia changes little, if at all, during geological time.
Hornblende—anthophyllite and hornblende—cummingtonite parageneses
Authors: Choudhuri A. 
Published: December 2006

SummaryThe associations hornblende and anthophyllite or cummingtonite are dealt with briefly in the light of experimental data and naturally occurring assemblages. On the basis of the distribution of Mg and Fe2+ in coexisting amphiboles and on the calculated and experimental slopes of a reaction in which the amphiboles hornblende and anthophyllite are formed a tentative P-T-x diagram is suggested for these parageneses.
Structural analysis of the most commonly encountered habit faces of calcite crystals from skarn deposits
Authors: Kashkai M.-A. , Aliev R. M. 
Published: December 2006

SummaryThis paper is a report on the various features of the crystallogenesis of calcite as shown in specimens collected from iron-ore skarn deposits. Although there are several forms, each showing a variety of habit, a detailed study shows that there is a unified sequence of successive habit substitution. A structural analysis of calcite based on P.B.C. (Periodic Bond Chain) vectors is then considered.
Plumbogummite-group minerals from Mull and Morvern
Authors: Bain D. C. 
Published: December 2006

SummarySandstones from Mull and Morvern, most of which are from the Greensand formation, have been shown by X-ray diffraction to contain minerals of the plumbogummite group in very small amounts in the < 1·4µm fraction. The minerals were concentrated by HF digestion of the clay minerals. X-ray spectrographic traces show concentrations of Sr, La, Ce, Yt, and Ba, and a semiquantitative spectrochemical analysis also shows a concentration of Ca and Pb and the presence of numerous rare-earth elements. Individual minerals, which have a complex composition and can not be assigned to any one named species, are disseminated throughout the rocks as particles with an estimated size of between 0·1 and 0·25µm.
Hallimond Lecture 1970 Electron-Optical study of phase transformations
Authors: McConnell J. D. C. 
Published: December 2006

SummaryThis paper is primarily concerned with the interpretation of phenomena associated with phase transformations in single crystals, as observed by current experiments using electron-optical techniques. An analysis of permissible metastable behaviour in such single crystals, in terms of lattice theory, is provided. The dominant role of symmetry in defining the constraints on permissible be-haviour of this kind is explained. The resulting theory indicates that, at low temperatures, permissible thermal fluctuations in local chemical composition, or order, become strongly degenerate and lead to the development of non-Bragg diffraction effects. The theory and practical study of the phenomena by electron microscopy are also described.The theory of metastable behaviour in a single crystal subject to symmetry constraints is then tested by re-examining the experimental data available for two systems that have been studied recently where such behaviour might be suspected. The first of these concerns the low-temperature behaviour of adularia, and the second deals with incipient exsolution phenomena in the alkali feldspar from a pantellerite. The data in each case appear to be compatible with the general theory proposed. Finally the theory is used to analyse the low-temperature behaviour of the intermediate plagioclase feldspars. In this case the theory indicates that both antiphase phenomena and schiller effects are associated with metastable behaviour in a system subject to strong symmetry constraints at low temperature. The implications of the analysis in relation to peristerite exsolution phenomena are discussed.
A microprobe study of chromites from the Andızlık-Zımparalık area, south-west Turkey
Authors: Engin T. , Aucott J. W. 
Published: December 2006

SummaryCompositional changes in chromites are shown to be related to the degree of alteration of the grains to ‘ferritchromit’. The chromium content of late stage pyroxenites and tremolites may be related to the development of the ‘ferritchromit’. Analysed grains from the chrome ores are shown to have a different chemistry to the accessory chromites in the peridotites.
Host control of recrystallized quartz grains
Authors: Ransom D. M. 
Published: December 2006

SummaryThe results of a petrofabric study on recrystallization of quartz in nature are presented and compared with recent experimental work. The orientations of newly recrystallized quartz grains are shown to be dependent on the orientation of host grains from or in which they grew. The results are compatible with the experiments of Hobbs (1968). The orientation of new grains appears to be unrelated to stress.
The Molteno meteorite
Authors: Frost Michael J. 
Published: December 2006

SummaryThe Molteno meteorite was seen to fall in South Africa in 1953. It is a howardite, with pyroxene varying from En76Fs22Wo2 to En38Fs58Wo4 and then to En33Fs26Wo41. Also present are twinned plagioclase (An 84·4%) and small quantities of olivine (Fa 12%), troilite, nickel-iron (Ni 4%), ilmenite, and an aluminian chromite with 0·71% V2O3. A bulk analysis and analyses of the metal, troilite, and combined silicates and oxides are given.
A metallographic study of the angra dos Reis (iron) meteorite
Authors: Axon H. J. , Waine C. V. 
Published: December 2006

SummaryThe Angra dos Reis (iron) has been studied metallographically and an attempt has been made to discuss the circumstances under which the following elements of structure formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rbabdites, rhabdite clusters, microrhabdites, cohenite, and remelted troilite. The remelted troilite is taken to indicate a shock event. However, since there are no metallographically visible indications of shock in the kamacite and since the back reflection X-ray diffraction pattern shows only very faint Debye-Scherrer arcs superimposed on a pattern of sharp spots, it is concluded that the shock event took place at a temperature that allowed shock effects to anneal out of the kamacite almost completely. A submicroscopic precipitate in the metallic matrix is observable with the electron microscope and may represent the final precipitation of phosphide from shocked kamacite.
Rhyodacite glass in Réunion basalt
Authors: Upton B. G. J. , Wadsworth W. J. 
Published: December 2006

SummaryThe local development of strongly oxidizing conditions during crystallization of a recent basalt lava lake on Piton de la Fournaise, Réunion, led to the production of approximately 15 % residual rhyodacite liquid. This was segregated into the vesicle cavities as the lava solidified, and congealed as a glass containing microlites of feldspar, clinopyroxene, and hematite. The rhyodacite is compared chemically with the residual glasses recorded from other basaltic and doleritic occurrences, and with the Mauna Kuwale rhyodacite of Oahu.
Phenocrystic olivines from the eastern Azores
Authors: Boone Gary M. , Fernandez Louis A. 
Published: December 2006

SummaryPhenocrystic and xenocrystic olivines and one olivine nodule sample, all from volcanics in the eastern Azores, range in composition from Fo87 to Fo69. Most are phenocrysts from the Nordeste alkali basaltic complex, eastern São Miguel Island, in which olivine-bearing rocks range from ankaramite to latite. CaO, MnO, and NiO trends are related to Mg-Fe contents, both for the concentrates as a whole, and also within analysed zoned crystals. It is shown that anomalous plots of Δ2ϑ(220LiF—062olivine) are related to pronounced Mg-Fe zonal gradients and, in samples from some flows, to mixtures of different generations of olivine. Regressions of Δ2ϑ vs. Fo (mol %) and FeO (wt %) for the least-zoned olivines are in close accord with those for Hawaiian olivines reported by Murata and others (1965).MnO percentages increase linearly with FeO; this and the Hawaiian trend are indistinguishable. Limited data for the most magnesian olivines indicate that NiO increases with FeO up to ∼ 15 wt % of FeO; the trend then decreases with further iron enrichment. This trend is apparent from other olivine data, and its relationship to the onset of pyroxene crystallization is discussed. CaO in olivine phenocrysts is inversely related to normative anorthite percentages in host rocks; the trend appears to be controlled largely by co-precipitation and fractionation of calcic plagioclase.
The herzenbergite-teallite series
Authors: Chang Luke L. Y. , Brice William R. 
Published: December 2006

SummaryEquilibrium relations of lead-tin sulphides in the system SnS-PbSnS2 were studied using a sealed silica-tube technique. A complete series of solid solutions forms in the system, and lattice parameters were found to vary lineally with composition. The melting temperature of the solid solution decreases with increasing amount of PbS from herzenbergite at 880 °C to teallite at 725 °C.Evidences were found to indicate the existence of this series of solid solution in ore deposits.
Chemical composition and physical properties of lithium-iron micas from the Krušné hory (Erzgebirge), Czechoslovakia and Germany. Part B: Cell parameters and optical data
Authors: Rieder M. , Píchová A. , Fassová M. , Fediuková E. , Černý P. 
Published: December 2006

SummaryUnit-cell dimensions and refractive indices of lithium-iron micas decrease with decreasing iron and increasing lithium. Indices β and γ as well as parameters a and b can be used to estimate the composition of lithium-iron micas but basal spacing and 2Vα are poor indicators of composition.The chemical composition of natural lithium-iron micas from the Krušné hory and the Erzgebirge along the Czechoslovak—German border was discussed in Part A of this study (Rieder et al., 1970). It was concluded that the composition and crystallography of these micas fit best the series siderophyllite-polylithionite. The compositions were expressed by the ratio A′ = LR/(LR+‘Fe’). In this expression, LR is the subscript value of Li or octahedral R3+ (whichever is the smaller) in the crystallochemical formula, ‘Fe’ is the sum of the values in the formula of Fe2+ and Mn2+. A′ therefore defines the position of a particular mica on the siderophyllite-polylithionite join. This paper deals with the correlation between composition, cell dimensions, and refractive indices.
Further investigations into the nature of the materials chlorophaeite and palagonite
Authors: Stokes K. R. 
Published: December 2006

SummarySpecimens of chlorophaeite and palagonite obtained from eight countries were examined using a variety of techniques. Investigations showed the materials to be not simple substances but multiphase composites. The confusion that existed in the literature necessitated a revision of the nomenclature and construction of criteria for identifying the two materials. Their nomenclature has been expanded: chlorophaeite to include the following phases; phase I, green and isotropic; phase II, golden yellow and isotropic; phase III, darker than phase II and anisotropic; a fourth phase, named associated material (A), microcrystalline, pale green and sometimes pleochroic. Similarly for palagonite, a golden yellow glassy phase, essentially basaltic glass (no new name needed); phase X, a hydrated phase slightly darker in colour than the glassy phase, also isotropic; phase Y, dark brown to orange, microcrystalline, anisotropic, found adjacent to phase X; associated material (M) green, anisotropic, often chlorite or chloritic. Both of the above descriptions were based on neotypes, established during the work. X-ray diffraction data for the two materials are given together with microprobe analyses of some of the phases of the two materials.
Synthetic ‘deweylite’
Authors: Speakman K. , Majumdar A. J. 
Published: December 2006

SummaryMaterials similar to the natural hydrated magnesium silicate mineral deweylite have been synthesized hydrothermally under low-temperature-low-pressure conditions from magnesia-silica gels. Optical, X-ray, infra-red, and DTA examinations have shown that both the natural and synthetic materials are mixtures of badly crystallized talc and badly crystallized serpentine. The mineral is thought to be a coarse mixture of these two components while the synthetic products are intimately interlayered. These materials are believed to be closely related to the hydrated magnesium silicates detected in high-magnesia cement hydration products.
Elba manganese ores and their origin, South-eastern Desert, U.A.R.
Authors: Basta E. Z. , Saleeb W. S. 
Published: December 2006

SummaryThe manganese ores of Elba, South-eastern Desert, occur as numerous veins located within a narrow belt trending N.W.-S.E. Three ore-types were distinguished: hard crystalline ore consisting mainly of pyrolusite or ramsdellite or both, banded colloform ore consisting mainly of psilomelane, and in places cryptomelane, and soft nodular ore consisting of todorokite with minor amounts of psilomelane (or cryptomelane), nsutite, and pyrolusite. Black calcite and baryte occur in some of the veins and increase with depth.Based on the field and mineralogical evidence the origin of the ore is discussed. It is suggested that the ore is a very low-temperature epithermal fissure deposit of black calcite type that occurs near the surface (oxidation zone) in brecciated zones along faults.
Crystal structure of coalingite
Authors: Pastor-Rodriguez J. , Taylor H. F. W. 
Published: December 2006

SummaryThe crystal structure of coalingite (Mg10Fe2(OH)24(CO3)·2H2O) has been determined using single-crystal X-ray methods. The mineral is trigonal, with space group Rm, aH = 3·12, cH = 37·4 Å, Z = ½, and (0001) cleavage. The structure is of a layer type, and is based on a structural element about 12·5 Å thick in the c-direction and consisting of two brucite-like layers and one disordered layer containing carbonate ions and water molecules and resembling those in sjögrenite and pyroaurite. The unit cell comprises three of these structural elements stacked together in the c-direction. The Mg2+ and Fe3+ ions are randomly distributed among all the octahedral sites of the brucite-like layers. The structure closely resembles those of sjögrenite and pyroaurite, but has two brucite-like layers between each CO32−−H2O layer where these have one. There is a tendency to random interstratification, and the crystals appear to contain intergrown regions of brucite and of sjögrenite or pyroaurite. Coalingite-K probably has a similar structure, but with three brucite-like layers between each -H2O layer; its idealized formula is probably Mg16Fe2(OH)36(CO3).2H2O.
Distribution of potassium feldspar polymorphs in intrusive sequences
Authors: Parsons Ian , Boyd Rognvald 
Published: December 2006

SummaryK-feldspar variation is described for four salic plutonic igneous complexes that show normative mineral variation in keeping with the course of fractionation predicted from experimental studies. These are a sodic syenite (Loch Ailsh), potassic syenites (Loch Loyal), a peralkaline syenite and soda granite complex (Puklen), and a calc-alkaline pluton (Foyers). Additional data are given for examples from the literature. Microcline becomes more abundant relative to orthoclase as members of these intrusive sequences approach thermal minima on the liquidus in the system Ab-Or-An-Qz. This relation exists irrespective of the compositional range of the rock suites, the bulk composition of the alkali feldspars, grain size, or field relations. Early orthoclase-bearing rocks retain orthoclase when enclosed as xenoliths in microcline-bearing rocks, or when cut by minor bodies of microcline-bearing rocks. The K-feldspar variation may reflect increasing water content or the peralkaline or peraluminous character of the fractionating magmas. These factors affect the feldspar structure at the time of initial crystal growth and dictate whether microcline will develop on cooling.
The stability and natural occurrence of margarite
Authors: Velde Bruce 
Published: December 2006

SummaryThe upper stability of margarite has been determined to be 450 °C at 1 kb and 530 °C at 2 kb total pressure (PH2O = Ptotal). Other experiments delimit in a general way the lower stability of this mineral and its paragenesis in more SiO2 rich compositions. The presence of the 060 reflection at 1·475 Å can be used to distinguish between margarite and paragonite or muscovite.
Twinning and intergrowth of olivine crystals in chondritic meteorites
Authors: Dodd R. T. , Calef Charles 
Published: December 2006

SummaryThe angular relationships among sets of olivine plates in barred chondrules were investigated on the universal stage to test a suggestion that such chondrules represent exsolution and inversion from a pre-existing jadeitic pyroxene. In one of sixty-seven cases studied, adjacent plates represent olivine twinning on (100); the others vary randomly and correspond to neither olivine nor pyroxene twinning. On this basis and from other evidence, we conclude that the mineralogy and texture of barred chondrules are primary and due to rapid crystallization of ultrabasic magma in a low-pressure environment.
Conditions for the formation of bayerite and gibbsite
Authors: Mchardy W. J. , Thomson A. P. 
Published: December 2006

SummaryAluminium hydroxide gels have been prepared by the hydrolysis of amalgamated aluminium in water and by precipitation from aluminium salt solutions with an anion exchange resin in the hydroxyl form. The products crystallizing from such gels have been examined by electron microscopy and by X-ray and electron diffraction. Bayerite crystallizes as cone or pyramid-shaped particles and gibbsite as hexagonal plates or prisms. Two types of gel are postulated. The first type, pseudoboehmite, predominates in the absence of acids, is uncharged and rapidly crystallizes to bayerite; the second type, pregibbsite gel, occurs in carboxylic acid solutions, is positively charged and, in the absence of inorganic anions, crystallizes slowly to gibbsite.
The relationship between optical properties and occurrence of some black tourmalines from Northern Nigeria
Authors: McCurry Patricia 
Published: December 2006

SummarySeventy-nine black tourmalines collected over a 12 000 km2 area of Precambrian to lower Palaeozoic rocks in northern Nigeria show a close correlation between maximum R.I., absorption colour, and occurrence in non-feldspathic micaceous schists and schorl rocks on the one hand, and in gneisses, migmatites, and feldspathic pegmatites on the other. Pleochroism is known to depend upon the total iron content and the Fe2+Fe3+ interaction. Colour variations may thus provide useful indicators of the geochemical environment during crystallization.Limited published data, supplemented by additional measurements on four tourmalines from outside the original area, suggest that similar correlations would be obtained for the rest of Nigeria.Selective processes of boron metasomatism may have been important in the association of different coloured tourmalines with feldspathic and non-feldspathic rocks, and the apparent lack of biotite in most tourmaline-rich rocks. The source of the boron probably lay within the upper Proterozoic to lower Palaeozoic metasedimentary belts with which the tourmaline is most strongly associated.
On aluminous and edenitic hornblendes
Authors: Leake Bernard E. 
Published: December 2006

SummaryBased on nearly 1500 published amphibole analyses the maximum possible Alvi in hornblendes is shown to increase with increase of Aliv. New analyses of hornblendes from amphibole-corundum rocks, with and without anorthite, are given and after critical examination of the available data it is concluded that the maximum verified Alvi-rich calciferous amphibole that approaches the closest to hypothetical tschermakite comes from a kyanite-bearing aluminous high-pressure-crystallized schist from Lukmanier, Switzerland. Pure natural edenite or ferroedenite is unknown, but a new analysis of the nearest known natural edenite, from Mysore, India, agrees with the postulated view that extraordinarily low temperatures are needed for edenite-ferroedenite crystallization, much below that possible in magmas and only rarely achieved in metamorphic rocks containing amphiboles. The limit of the approach of igneous hornblendes to edenite-ferroedenite and tremolite-ferroactinolite is outlined.At least 1100 °C is required for complete expulsion of water from some amphiboles.