bluuebunny/crossref_metadata_2025_split huggingface dataset:
Archimedean polyhedra as the basis of tetrahedrally-coordinated frameworks
Authors: Moore Paul B. , Smith Joseph V. 
Published: December 2006

SummaryThe linkage of Archimedean polyhedra has been studied to provide trial models for tetrahedrally-coordinated structures such as zeolites. The cuboctahedron, rhombicuboctahedron, snub cube, icosidodecahedron, rhombicosidodecahedron, and snub dodecahedron cannot be used because four edges meet at a corner. The truncated tetrahedron, truncated cube, and truncated dodecahedron have triangular faces, and are unlikely to occur in silicate frameworks because of the instability of 3-rings. The truncated icosahedron and truncated icosidodecahedron have fivefold symmetry and cannot form four-connected frameworks with lattice symmetry. The truncated octahedron and truncated cuboctahedron may be linked either directly, in combination, or with square, hexagonal, or octagonal prisms. There are nine structures of which four are represented by sodalite, Linde A, faujasite, and ZK-5. The other five have the following properties: truncated octahedra linked H(H-S),Fd3m, a17·5 Å; truncated octahedra linked H′(H-S) and (H-H),P63/mmc, a12·4,c20·5 Å; truncated octahedra linked H′(H-S) and (H-H),P63/mmc, a17·5,c28·5 Å; truncated cuboctahedra linked O′(S-S),Im3m, a15·1 Å; truncated octahedra linked to truncated cuboctahedra H′(S-S),Fm3m, a31·1 Å. The first symbol specifies the linking unit (H hexagon, H′ hexagonal prism, O′ octagonal prism) while the symbols in brackets specify the type of faces opposing across the contact (S square).
Notes on a new occurrence of stilpnomelane from North Wales
Authors: Matthews D. W. , Scoon J. H. 
Published: December 2006

SummaryAn occurrence of stilpnomelane in calcite veins cutting an Ordovician sedimentary iron-ore body has yielded good material for optical and chemical study; data for both ferro- and ferri-stilpnomelane are presented. Associated pyrrhotine, ilmenite, and apatite are briefly described, and a chemical analysis of the apatite shows it to be an extremely pure fluorapatite.
Mboziite, a new sodic amphibole end-member
Authors: Brock P. W. G. , Gellatly D. C. , von Knoebing O. 
Published: December 2006

SummaryAn amphibole occurring in the Mbozi syenite–gabbro complex in SW. Tanganyika approaches very closely to the theoretical end-member Na2Ca;it has α 1·705, pale to light yellow, β 1·713, deep blue-green, γ 1·715, deep blue to green to black, with γ ∥ [010] and β : [001] about 7 to 14°; absorption γ > β ≫ α, with the maximum absorption on (010) at 9 to 12° to [001]. The mineral shows anomalous bright orange-red interference colours and incomplete extinction in sections parallel to (010) even in monochromatic light. X-ray powder data are given. A very similar amphibole occurs in the Darkainle nepheline-syenite complex, Borama district, Somali Republic.
A numerical system of classification for chlorites and septechlorites
Authors: Phillips W. R. 
Published: December 2006

SummaryOnly two, or at most three, variables can be considered on a two-dimensional composition diagram; six variables must be fixed to completely define a variety of the chlorite or septechlorite groups. The positions of tetrahedral coordination may be described by a single variable and positions of sixfold coordination require three independent variables for complete definition. The number of OH− ions is probably very near the theoretical value of eight, however, it may vary somewhat from this value, and, in so doing, influences the ratio of trivalent and bivalent cations in octahedral coordination.The normal 14 Å chlorites and 7 Å septechlorites have traditionally been associated together and, although they represent two distinct structural groups, are considered together for classification purposes, since they share many identical variety compositions; a sixth variable denotes structural type, as determined by X-ray powder diffraction or D.T.A.Each chlorite or septechlorite variety can be described by a numerical notation (chlorite number) consisting of six units and, by dividing the chlorite numbers into units according to accepted nomenclature, each possible chlorite composition can be assigned a variety name, and all variety names can be assigned to a definite composition range.
Layered structure in rocks of the Jotunheim Complex, Norway
Authors: Battey M. H. 
Published: December 2006

SummaryTwo-pyroxene feldspar gneisses and associated ultramafic rocks of the Jotun Kindred in Southern Jotunheimen display mineralogical layering believed to be of original igneous origin. The geological structure of part of the stratiform massif is described, and is shown to provide a basis, hitherto lacking, for systematic study of the mineralogical and chemical variation of the suite.
Hornblendes from some basic hornfelses in the New England region, New South Wales
Authors: Binns R. A. 
Published: December 2006

SummaryWith progressive increase in grade of contact metamorphism, aluminous hornblendes in some New England basic hornfelses change from a pale blue-green variety with ragged actinolitic habit, to a deeper bluish-green variety, then to a deeply coloured brownish type with granular habit. At all stages the coexisting plagioclase is appreciably calcic. No outer aureole of albite-epidote-actinolite hornfels has been recognized. The higher grade hornblendes are richer in alkalis and titanium, and poorer in octahedrally co-ordinated aluminium than those formed at low grades. Two analysed hornblendes display an unusual excess of calcium, which occupies the Y site, and another has a very high content of ferrous iron and potassium.
Trachytes and their feldspar phenocrysts
Authors: Carmicrael I. S. E. 
Published: December 2006

SummaryThe compositions of the groundmass and of the plagioclase and sanidine phenocrysts of a series of over- and under-saturated trachytes indicate that plagioclase will precipitate at some stage in the crystallization interval of all calcium-bearing potassic trachytes. Using this data obtained from natural salic liquids, a concept of crystallization within the system CaA2Si2O8-NaAlSiO4-KAlSiO4-SiO2 may be obtained.
Titania and alumina content of oceanic and circumoceanic basalt
Authors: Chayes Felix 
Published: December 2006

SummaryMost circumoceanic basalts contain less and most oceanic basalts considerably more than 1·75% of TiO2. The difference of TiO2 averages is large enough to require rejection of the hypothesis that circumoeeanie basalt results from the assimilation of sial by oceanic basalt.
Ages of uraninite and Coffinite from south-west England
Authors: Darnley A. G. , English T. H. , Sprake O. , Preece E. R. , Avery D. 
Published: December 2006

SummaryThe mode of occurrence of uraninite, pitchblende and coffinite at five localities in south-west England is described. Chemical and isotopic analyses of concentrates containing these minerals provide the following 206Pb/238U ages (My.): uraninite, South Crofty, Cornwall, 277 ± 10; uraninite, Geevor, Cornwall, 223 ± 5; pitcbblende-coffinite, King's Wood, Devon, 206 ± 5; pitchblende, Wheal Bray, Cornwall, 165 ± 4; pitchblende, South Terras, Cornwall, 474 ± 2; coffinite, Geevor, Cornwall, c. 45 (chemical analysis only). These results are compatible with geological and mineralogical evidence. Consideration of these and other results indicates that there were at least three periods of uranium mineralization in south-west England, at c. 290 My., c. 225 My., and c. 50 My. Other intermediate ages may also be valid but further work is required to substantiate these.
Clinopyroxenes of the gabbro cumulates of the Kap Edvard Holm complex, east Greenland
Authors: Deer W. A. , Abbott D. 
Published: December 2006

SummaryThe major part of the Kap Edvard Holm complex consists of two series of conspicuously banded gabbroic rocks. The primary minerals of both lower and upper layered series show a progressive change in composition, from higher to lower temperature phases, with increasing height in the complex. Minor fluctuations in the differentiation of the two series occur but the division of the layered rocks into the lower and upper series is based on abrupt and major changes in the compositions of the pyroxenes, olivine and plagioclase. This break is correlated with the injection of a large volume of undifferentiated magma which occurred after much of the lower layered series had consolidated, and from which the rocks of the upper layered series were formed. Twelve pyroxenes, five from the lower and seven from the upper layered series have been analysed; the relationships between their optical properties and chemical composition, and between the cell parameters and composition are considered. The crystallization trend of the pyroxenes is compared with that of the Skaergaard calcium-rich pyroxenes; it is suggested that the restricted enrichment in iron shown by the Kap Edvard Holm pyroxenes may be related to the higher water-vapour pressures which prevailed during much of the period of crystallization.
New petrographical data on the Shiant Isles picrite
Authors: Drever H. I. , Johnston R. 
Published: December 2006

SummaryA recent bore-hole through the Shiant Isles picrite established the existence of 45 feet more of the picritic facies, and also the lower margin of the silt, at a point almost vertically below the exposed 35 feet previously investigated. In the light of new field and laboratory information the pieritic facies is briefly re-examined and its origin discussed.
Bustamite, rhodonite, spessartine, and tephroite from Meldon, Okehampton, Devonshire
Authors: Howle R. A. 
Published: December 2006

SummaryChemical analyses together with optical and physical properties are given for ferroan bustamite, rhodonite, spessartine, spessartine-grossular, and tephroite from contact metamorphosed cale-silicate rocks of the Meldon Railway Quarry, Okehampton. The compositions of these minerals are compared to those from the Treburland manganese mine, Cornwall. An analysis is also given of a spessartine from a pyrrhotite-spessartine skarn rock from the nearby Meldon aplite quarry.
The problem of the potash-rich basaltic rocks
Authors: Joplin Germaine A. 
Published: December 2006

SummaryIt is suggested that the name shoshonite be revived for a group of potash-rich basalts and that the magma from which monzonites, potash-rich syenites, many lamprophyres, nepheline monzonites, shonkinites, eovites, ijolites, leucite basalts, leucitophyres, etc., have crystallized be called the shoshonite magma-type. This series shows parallels with the alkali basalt magma series, and the question of the relation of the two magma-types is discussed.The name latite is discussed and rejected as a name for this potash-rich magma type. It is further shown that rocks of this composition invade geosynelinal regions that have been recently stabilized, one group of shoshonites being associated with an environment that is still subjected to minor folding and showing some relation to the cale-alkaline rocks, the other a true alkaline suite associated with non-orogenic conditions.
The contamination of a gabbro by Carboniferous Limestone at Carlingford, Co. Louth
Authors: Le Bas M. J. 
Published: December 2006

SummaryAmongst the layered basic rocks of the Carlingford complex, is a gabbro which has been contaminated by a limited amount of Carboniferous Limestone. The clinopyroxene (Ca49Mg33Fe18) produced in the gabbro is similar to that found in teschenitic gabbros. Such features as the instability of olivine distinguish this contaminated tholeiitic gabbro from true alkaline types. The production of aluminous augite is discussed, and comparison is made with the basic rocks of Scawt Hill and Gunnedah. Analyses of the contaminated gabbro and contained pyroxene are given.
The cathodo-luminescence of minerals in thin section
Authors: Long J. V. P. , Agrell S. O. 
Published: December 2006

SummaryThe cathodo-luminescence of minerals in thin sections of rocks has been examined with the aid of an electron-probe microanalyser and also with a simple electron source producing an unfocused beam. Experimental details of the technique are briefly described and colour photographs, taken at a primary magnification of 30 times, are included. The observed variations in colour and intensity of luminescence are interpreted in the light of electron-probe and spectrochemical determinations of trace elements. Applications of the technique are discussed.
The magnesium aluminium borosilicates: kornerupine and grandidierite
Authors: McKie Duncan 
Published: December 2006

SummaryA new occurrence of kornerupine in the skarn zone at Mautia Hill, Tanganyika, has yielded unit-cell dimensions a 16·100, b 13·767, c 6·735 Å, density 3·297, and composition Na0·01Mn0·01Ti0·02Mg3·69Fe0·37IIIAl6·36Si3·71B0·41O21·75(OH)0·25. The unit-cell clearly contains 88 anions rather than the 86 proposed previously. Grandidierite from Sakatelo, Madagascar, has unit-cell dimensions a 10·978, b 10·335, c 5·760 Å, space group Pna21 or Pnam, density 2·976, and composition Fe0·12IITi0·01Mg0·88Fe0·03IIIAl3·00Si1·00B0·97O9·00. The unit-cell contains 36 anions and the structure appears to involve A106 chains parallel to the c-axis.
On the chemistry of pillow lavas and the origin of spilites
Authors: Vallance T. G. 
Published: December 2006

SummaryTwenty-five new analyses of 10 spilitic pillows from the British Isles offer evidence of considerable variability in distribution of components, notably Si, Na, Mg.Fe2+, Ca, Fe3+, and water. Selvedges of pillows have compositions strongly contrasted with but essentially complementary to those of cores. Redistribution of components is believed to have occurred during devitrification. Geosynclinal spilites are regarded as basalts which have suffered such redistribution under conditions of diagenesis or low-grade metamorphism.
The part played by tholeiitic magma in the Carbo-Permian vulcanicity of central Scotland
Authors: Walker Frederick 
Published: December 2006

SummaryThe end-Carboniferous quartz-dolerites form a curious tholeiitic interlude in the alkaline olivine-basalt vulcanicity which characterized central Scotland from the top of the Old Red Sandstone to the Lower Permian. The relationship of the two magma-types is discussed in the light of fresh evidence.
Gyrolite and reyerite from ’S Airde Beinn, northern Mull
Authors: Cann J. R. 
Published: December 2006

SummaryReyerite is found in close association with gyrolite in the metamorphic aureole of the volcanic plug of 'S Airde Beinn, northern Mull, and has apparently been formed by metamorphism of the gyrolite. The gyrolite, with a composition close to Ca16Si24O60(OH)3.14H2O, closely approaches trigonal symmetry with a 9·76±0·02 Å and c 3 × 22·26±0·1 Å; biaxial with a small 2V and α 1·537, β 1·547, γ 1·549. The reyerite is trigonal with a 9·76±0·02 Å, c 19·10±0·04 Å and space group Pω 1·568 and ε 1·563, and the unit cell contains about 14 atoms of Ca, 24 of Si (with some substitution by 4(OH)−), and 14H2O as (OH)− and H2O.
The thermal decomposition of crocidolite from Koegas, South Africa
Authors: Hodgson A. A. , Freeman A. G. , Taylor H. F. W. 
Published: December 2006

SummaryWhen crocidolite (fibrous riebeckite, Na2Fe3+2Fe2+2·6Mg0·4Si8O22(OH)2 approx.) is heated in argon or nitrogen at 50–400°C, uncombined water is lost. The tensile strength drops sharply at 300–400°C. At 500–600°C under static, or 570–700°C under dynamic conditions, an endothermic dehydroxylation yields an anhydride with a structure close to that of the initial material. At about 800°C, the anhydride decomposes endothermically, giving acmite, cristobalite, a spinel, and liquid. At 950–1000°C the acmite decomposes. Melting is extensive by 1050°C.On heating crocidolite in oxygen or air, uncombined water is again lost below 400°C. At 300–450°C (static), or 400–600°C (dynamic), hydrogen ions and electrons are lost, to give an oxyamphibole, Na2Fe3+4Fe2+0·6Mg0·4Si8O24. The process is exothermic and probably occurs by proton and electron migration, as suggested by Addison et al. (1962). At 600–950°C the oxyamphibole decomposes endothermically, and most of the remaining Fe2+ is oxidized, giving acmite, hematite, cristobalite, and a spinel. The spinel has largely disappeared by about 950°C, while at 975–1000°C the acmite also decomposes and melting begins.When crocidolite is heated in hydrogen, no change is detectable by X-rays below 530°C, when the amphibole decomposes to give mainly a pyroxene, metallic iron, cristobalite, and liquid. The same products are detectable up to at least 850°C; the proportion of metallic iron increases with temperature.With the exception of metallic iron, all the crystalline products formed, whether under neutral, oxidizing, or reducing conditions, show varying degrees of preferred orientation. This could be explained if the reactions occur mainly by the migration of cations through relatively undisturbed oxygen frameworks.
Rhombohedral molybdenite from the Minas da Panasqueira, Beira Baixa, Portugal
Authors: Horrell Clark A. 
Published: December 2006

SummaryRhombohedral (3R) molybdenite has hitherto been reported from only one locality. Its mode of occurrence at a new locality is reported in this paper. At Panasqueira it occurs as a rare accessory in greisenized granite with which wolframite-cassiterite-quartz veins are associated. In the veins themselves only normal hexagonal (2H) molybdenite has been detected.
The identification, mode of occurrence, and quantitative determination of crystalline phases in granulated blast-furnace slag
Authors: Steyn J. G. D. 
Published: December 2006

SummaryThis paper describes a technique for the identification and quantitative determination of crystalline phases in granulated blast-furnace slag by means of incident light microscopy on polished and etched samples. The crystalline phases (including periclase) observed in high-magnesia granulates are reported and their mode of occurrence illustrated.
Intergrowths in ilmenite of the beach sands of Kerala
Authors: Rao N. K. , Rao G. V. U. 
Published: December 2006

SummaryA detailed study of ilmenite concentrates from Chavara and Manaalakurichi deposits has brought to light several interesting textures traceable to exsolution, eutectic crystallization, and replacement and alteration. Magnetite-ilmenite, magnetite-ilmenite-picotite, ilmenite-picotite, ilmenite-hematite, and ilmenite-rutile exhibit exsolution intergrowths. Part of the ilmenite seems to have been formed either by oxidation of ulvöspinel or from a cubic phase of ilmenite by monotropic inversion. Some of the ilmenite-hematite intergrowths display either an emulsoid or a triangular type of texture. Subgraphic intergrowth is observed between ilmenite-magnetite and ilmenite-rutile, suggesting an eutectic relationship between them.Magnetite-hematite, magnetite-goethite, and magnetite-maghemite intergrowths are the result of alteration of magnetite. Sphene also partly replaces some ilmenite grains.The proportion of ilmenite grains with and without intergrowths and the probable origin of the intergrowths and their effect on the marketability of ilmenite concentrates are discussed in the paper.
Oriented transformation of manganite during heat treatment
Authors: Dasgupta D. R. 
Published: December 2006

SummaryThe transformation of manganite during heating has been studied by single crystal X-ray diffraction methods. It is observed that manganite transforms into pyrolusite keeping its original axial directions parallel to those of the transformed phase. Pyrolusite then transforms into Mn2O3 with its [001] ‖ [110] or [100] of Mn2O3; of Mn2O3 and [010] ‖ [001] of Mn2O3. Evidence of an intermediate product in the pyrolusite → Mn2O3 reaction has been found.
Mechanism of formation of forsterite and enstatite from serpentine
Authors: Brindley G. W. , Hayami Ryozo 
Published: December 2006

SummaryForsterite formed from serpentine powders at various temperatures up to 800° C has been measured quantitatively by X-ray diffraction. The results are considered in relation to a reaction mechanism proposed by Ball and Taylor and are shown to be inconsistent with the details of this mechanism. An alternative mechanism is proposed by which all or nearly all the Mg ions together with some of the Si ions liberated in the reaction zones where water is formed migrate into regions where forsterite is formed. This mechanism is in closer accord with the experimental results. The retarded development of enstatite until temperatures above 1000° C are used is attributed to the nature of the reaction by which it is formed, namely a reaction between forsterite and silica.
The high-temperature behaviour of beryl melts and glasses
Authors: Miller R. P. , Mercer R. A. 
Published: December 2006

SummaryThe course of all crystalline structural changes undergone by the mineral beryl, its melt and glass, has been followed as a function of widely differing but accurately known thermal history. Non-equilibrium ordering processes have been characterized by new techniques in high-temperature microscopy.The relative influence that beryllium and aluminium ions exert on the phase changes has been established by studies on synthetic melts and glasses representing hypothetical beryls of differing ratios of Be2+:Al3+ ions.The dynamic changes between the oxide and orthosilicate structures into which the systems reconstitute include the formation of a metastable hybrid beryllium aluminium silicate, which is viewed as a beryllium-containing mullite. The crystallochemical changes have been interpreted in terms of a structural model of the melts and glasses that is shown to be consistent with the ordering effects predicted from the field strengths of the cations.
The mineralogy of the potassium–barium feldspar series
Authors: Roy N. N. 
Published: December 2006

SummaryVariation diagrams for the optic properties and densities of natural specimens within the series have been determined. They focus attention on two composition regions at about 45 % Cn and 65 % Cn. The significance of the first of these is uncertain, but it is suggested that the discontinuity at 65 % Cn is related to structural changes that take place at this composition.
Mineralogical and radiometric studies of monazite and sphene occurrences in the Namib Desert, South-West Africa
Authors: Burger A. J. , von Knorring O. , Clifford T. N. 
Published: December 2006

SummaryMonazite and sphene from the central zone of the Damara orogen of South-West Africa, have yielded ages of 500 ± 20 Myr and 600 ± 25 Myr respectively; these results are discussed in relation to the late Precambrian to early Palaeozoic tectono-thermal history of the region. Although chemically similar to that found in carbonatites, the monazite is probably genetically related to the widespread granitic pegmatites that characterize the central zone of the orogen.
The mineralogy of metamorphosed basic rocks from the Willyama Complex, Broken Hill district, New South Wales. Part II. Pyroxenes, garnets, plagioclases, and opaque oxides
Authors: Binns R. A. 
Published: December 2006

SummaryChemical and optical data are presented for the orthopyroxenes, clinopyroxenes, garnets, plagioclases, and opaque oxides in high-grade regionally metamorphosed basic rocks and their garnetiferous associates from the Willyama Complex. Exsolution phenomena in the pyroxenes have been studied by X-ray diffraction methods and with the electron probe micro-analyser. The (001) lamellae in one lime-rich clinopyroxene are clinohypersthene. Comparison of the Willyama and other granulite facies clinopyroxenes with those of slowly cooled basic igneous rocks suggests that their chemical compositions may be used as guides to temperature conditions during formation. Willyama plagioclases are complexly twinned and possess intermediate structural states.