bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentary analcime rocks and sodium-rich gneisses
Authors: Coombs D. S. 
Published: December 2006

SummaryAs indicated by Tilley (1925), albite-rich schists and gneisses can inherit their abnormal chemical characteristics from sediments that are proving to be by no means rare. They may be rich in detrital sodic plagioclase or they may contain authigenie analcime. Some sedimentary analcime rocks (‘analcimolites’) carry normative nepheline and so offer potential parent rocks for nepheline-bearing gneisses provided that, in these gneisses, SiO2 ⩾ (4Na2O+6K2O) in molecular proportions. The chemistry and occurrence of soda-rich sediments are reviewed. Some New Zealand occurrences are newly described and hitherto unpublished analyses are presented for porphyroblastic albite schist and felsitic volcanic arenite from Otago, and for analcime-rich sediments from four localities.
An X-ray powder method for the estimation of (K, Ba) feldspars
Authors: Gay P. 
Published: December 2006

SummaryExamination of previous physical methods of estimating the barium-content of these feldspars showed that they are generally unsatisfactory. A new variation diagram is constructed correlating BaO content and values of d132 determined from diffractometer records. It is estimated that the BaO content of these feldspars can normally be determined to about 2–3% by using this diagram.Some of the problems of the mineralogy of the series are reviewed in the light of the experimental results, in particular the effect of polymorphic changes on the variation diagram. Some experimental evidence of the effect of different structural states upon the value of d132 is obtained, and the limitations imposed upon the method by the existence of such states are discussed.
Phase-equilibrium studies in the system NaAlSiO4 (nepheline)–KAlSiO4 (kalsilite)–SiO2-H2O
Authors: Hamilton D. L. , MacKenzie W. S. 
Published: December 2006

SummaryPhase-equilibrium relations have been determined at 1000 kg/cm2 water pressure for compositions within the system NaAlSi3O8-KalSi3O8-NaAlSiO4-KAlSiO4 in the area adjacent to the temperature minimum. The composition and temperature of the minimum are Ne50Ks19Qz31 and 750° ± 7° C respectively. The compositions of 102 plutonic rocks and 122 extrusive rocks, from Washington's tables, that carry 80% or more of normative Ab + Or + Ne have been plotted; the areas of high density show a marked similarity to the positions of the low-temperature regions of the synthetic system and suggest that many undersaturated rocks are derived by fractional crystallization from a trachytic magma.
Scawtite and its synthesis
Authors: Harker R. I. 
Published: December 2006

SummarySince its discovery by Tilley in 1930, scawtite has been recognized in several locations in regions of metamorphosed siliceous limestones. Scawtite is believed to be the same as CSH(A) and, as such, has been synthesized sporadically many times during runs in the CaO-SiO2-H2O system where slight contamination from CO2 has occurred. Attempts to synthesize scawtite were successfully carried out at low partial pressures of CO2 in an excess of water. The stability of selected scawtite compositions lies between 140 and 300° C, and above saturated steam pressures is not pressure-dependent, at least up to 50 000 psi. The scawtite facies (2) lies between the tobermorite-calcite facies (3) and the xonotlite-calcite facies (1). A hydration series exists from (1) to (2) to (3).
A second occurrence of lyndochite
Authors: Horne J. E. T. , Butler J. R. 
Published: December 2006

SummaryLyndochite from Tura dukas, 35 miles north of Nanyuki, Kenya, agrees closely with the type material from Canada in its chemical analysis, in the distribution of the rare earths, and in X-ray diffraction data for powder after heat treatment. The mineral is compared and contrasted with aeschynite. Uranium-poor euxenite is intimately associated with lyndochite at the type locality.Since its discovery over thirty-five years ago, lyndochite has remained unrecorded outside its type locality of Lyndoch Township in Ontario, Canada. Its distinctive chemical composition sets it apart from almost all other Ti-rich metamiet niobates and, despite the many analyses that have been made on rare-earth niobate-tantalates, specimens that could have been regarded as similar to or approximating to lyndochite have rarely been mentioned. Its unusual characteristics include high ThO2 (about 10%) and appreciable rare-earth oxides (about 20%) with a lanthanon assemblage showing a peak concentration of Nd (and Ce), rather than any of the heavy lanthanons. The proportions of TiO2 (about 20%) and (Nb,Ta)2O5 (about 40%) are comparable to those in numerous niobate-tantalates, but are only associated with the percentages of ThO2 and Re2O3 mentioned above in some members of the aesehynite-priorite series. The lyndochite now described is chemically very close indeed to the Canadian lyndochite, and both specimens give closely similar X-ray diffraction patterns (after suitable heat treatment) which are distinct from those of any other metamict mineral.
Weddellite in modern sediments, Florida
Authors: Hutton C. Osborne , Taft William H. 
Published: December 2006

SummaryEuhedra of weddellite have been recognized in modern, unconsolidated sediments collected from depths of water not exceeding one fathom, along the south-east coast of Florida. For weddellite, the following data have been determined: crystals simple with r {011} accompanied by a {010} in some cases; goniometric axial ratio is a:c = 1:0·593 (meas.), 1:0·5938 (calc.); a0 12·360 Å, c0 = 7·340 Å; space group I4/m, I4 or I4̅; α 1·529, γ = 1·544, δ = 0·015, uniaxial, positive; d22°C = 1·941. Heat treatment of weddellite led to development of whewellite, calcite, and calcium oxide in turn as higher temperatures were employed; fully indexed X-ray diffraction powder data are given for weddellite, in addition to d-spacings and intensities for whewellite.It is suggested that weddellite developed in the calcareous Florida sediments under conditions of storage over a two-year period, and ahnost certainly was not a constituent of those sediments at the time of collection. This raises the question whether weddellite was present in the Weddell Sea material at the actual time they were recovered by members of the Scotia Expedition.
The significance of the gabbroic xenoliths from Gough Island, South Atlantic
Authors: Le Maitre R. W. 
Published: December 2006

SummaryThe petrography and mineralogy of a series of gabbroic xenoliths, consisting essentially of varying proportions of olivine, clinopyroxene, orthopyroxene, and plagioclase, are described from Gough Island. These are compared with xenoliths from other oceanic localities. Four new analyses of xenoliths and six of pyroxenes are presented, together with some partial analyses of plagioclases. It is concluded that the xenoliths are derived from the mantle above the magma source area. The composition of the mantle in this region is thought to be that of an olivine-tholeiite.
Barringtonite—A new hydrous magnesium carbonate from Barrington Tops, New South Wales, Australia
Authors: Nashar Bebyl 
Published: December 2006

SummaryBarringtonite, a new hydrous magnesium carbonate of composition MgCO3,2H2O, is recorded from Sempill Creek, Barrington Tops, New South Wales, where it occurs as nodular encrustations on the surface of olivine basalt. The mineral is triclinic, biaxial positive, has refractive indices α = 1·458, β = 1·473, γ = 1·501, 2Vγ = 73° 44′, and using Ito's method (1949) cell dimensions α = 9·155 Å, b = 6·202 Å, c = 6·092Å, α = 94· 00′, β = 95· 32′, and γ = 108° 72′. The three strongest lines on an X-ray powder photograph give d values of 8·682, 3·093, and 2·936 Å.
Basalts from the deep ocean floor
Authors: Nicholls G. D. 
Published: December 2006

SummaryBasalts dredged from the floor of the deep ocean show general tholeiitic affinities. Some samples are rich in aluminium and of very similar composition to the Warner high-alumina basalt from California. Both olivine tholeiite and high-alumina basalt have been found in the form of glass in dredgings from the Mid-Atlantic Ridge, indicating that liquid magmas of both compositions have been erupted on to the sea bed in this area. In explanation of this association a tentative hypothesis of fractional melting of hydrated upper mantle material is proposed. It is suggested that under the mid-ocean ridges the ‘basaltic fraction’ of the mantle is locally in the form of an amphibole. Fractional incongruent melting of this amphibole appears to be a possible explanation of the range of composition encountered in dredged glass samples.
Yellow apophyllite from Korsnäs, Finland
Authors: Sahama Th. G. 
Published: December 2006

SummaryThe honey-yellow apophyllite from Korsnäs, Finland, for which chemical, optical, and X-ray data are given, shows a complex twinning. An inner penetration twin is surrounded by two outer penetration twins. The twin laws have been established. The prism faces of the complex crystal are not (100) as conventionally taken for apophyllite but (520). The spacegroup P4/mnc commonly accepted for apophyllite could not be confirmed. It is suggested that the mineral is only pseudotetragonal, the true symmetry possibly being orthorhombic with space group Pnn2 or Pnnm.
The form and internal structure of the alkaline Kangerdlugssuaq intrusion, East Greenland
Authors: Wager L. R. 
Published: December 2006

SummaryThe Kangerdlugssuaq intrusion (68′ 20′ N. 32′30″ W., roughly circular and 33 km across) is of Tertiary age, like the nearby Skaergaard intrusion. At the present level of erosion the outer part is of nordmarkite and inwards there are successive rings of transitional pulaskite (without quartz or nepheline), main pulaskite and, in the centre, foyaite. The different rock types are due to gradual changes in the amounts of certain of the minerals and there are no sharp junctions such as would be expected to result from successive injections.Zones of inclusions of basalt, fallen from above, dip inwards at 30 to 60° and, in places, there is a platy parallelism of the tabular alkali feldspars dipping similarly inwards. The three-dimensional form of the intrusion is pictured as resembling a pile of saucers of decreasing size, the sequence of formation being from the outer saucer of nordmarkite to the inner, and smaller saucers of increasingly nepheline-rich syenites. Bottom accumulation of crystals is postulated to explain the disposition of the rock types, but the cause of the succession from quartz-bearing to felspathoidal syenites remains uncertain.
Prehnitization in the Yahgan Formation of Navarino Island, southernmost Chile
Authors: Watters W. A. 
Published: December 2006

SummaryUpper Mesozoic geosynclinal sedimentary rocks, mainly of volcanic (andesitic) derivation, show widespread prehnitization caused by very low grade metamorphism (burial metamorphism). The sediments, which include greywackes, argillites, cherty rocks, and occasional limestone concretions and thin beds, appear little altered in hand specimen and in the field despite the wide extent of recrystalli-zation. Besides prehnite, secondary minerals include quartz, albite, chlorite, sericite, calcite, and sphene. The different modes of occurrence of the prehnite are described and briefly discussed. The alteration of the rocks is compared with similar wide-spread prehnitization recorded in probably correlative rocks on South Georgia.
The thermal disintegration of crocidolite in air and in vacuum
Authors: Patterson J. H. 
Published: December 2006

SummaryThe thermal disintegration of crocidolite has been investigated with X-ray powder and rotation photographs. Initial disintegration products include monoclinic pyroxene, iron oxide phases, and eristobalite as a pseudomorph of the original fibre bundles but at about 1000° C fusion occurs due to incongruent melting of the pyroxene. The products are strongly oriented along the fibre axis and full orientation relationships have been deduced with the aid of structural models. From these relationships it is suggested that regions of the amphibole structure on (100) are retained in the product phases without change in orientation.
A study of uvarovite
Authors: Isaacs T. 
Published: December 2006

SummaryUvarovite and its relationships with grossular and andradite have been studied in order to understand better the geochemistry of uvarovite. Synthese have been carried out under both dry and hydrothermal conditions; a solid solution with grossular was obtained under both conditions, but with andradite only under hydrothermal conditions. The results are discussed in relation to the chemistry of uvarovite.
A scheme of cation distribution in the amphiboles
Authors: Ghose Subrata 
Published: December 2006

SummaryThe four principles governing the cation distribution in various octahedral metal sites in the amphibole structure are: Ionic size—the M4 position prefers large cations like Ca2+, Na+; charge balance—when the M4 position is occupied by a monovalent ion, like Na+, Li+, the neighbouring M2 position is occupied by a trivalent ion like Al3+, Fe3+; role of the strongly polarizing cations—cations like Fe2+ prefer the M4 site, since they tend to form covalent bonds with the O4 oxygens; and the role of the (OH) ions—these form part of the brucite layer and repel large or strongly polarizing cations, which tend to distort the regularity of the sheet structure.The Al-Si distribution in the two different tetrahedral sites are governed by three principles: relief of the Si-O-Si bond strain—Al3+ in the Si1 site causes fewer Si4+ cations to share more than two anions with other Si4+ cations; charge balance—with the introduction of alkali ions in the ‘A’ position, Al3+ is introduced in the Si1 position, since the coordinating oxygens around the A position mostly belong to Si1; and steric considerations—occupation of the M4 site by a large cation tends to rotate the Si2 tetrahedron anticlockwise; Al3+ substitution in the Si1 site rotates the Si1 tetrahedron clockwise and thus the regularity and the constancy of the repeat distance of the silicate double chain is maintained.Based on these principles, a scheme of cation distribution in the M1, M2, M3, M4, A, Si1, and Si2 positions in the amphibole structure has been derived for most of the common amphibole varieties, except richterite, whose position is anomalous from a crystallochemical point of view.
Alteration products of olivine and pyroxene in basalt lavas from the Isle of Mull
Authors: Fawcett J. J. 
Published: December 2006

SummaryFlood basalts of the Isle of Mull were sampled in areas outside the metamorphic aureole of the central intrusions. Alteration products of olivine and pyroxene in these rocks are talc, chlorite, serpentine, iron oxides, brucite, calcite, and ‘iddingsite’. Plagioclase feldspar in the same rocks is unaltered. ‘Iddingsite’ is less common than mixtures of chlorite and serpentine.In two flows the only alteration product near the bottom is ‘iddingsite’ but at higher levels in the same flow green ehloritic material replaces olivine. This variation is accompanied by an increase in the FeO/Fe2O3 ratio in the rock towards the flow top. Green alteration products may be converted to material optically identicaI with ‘iddingsite’ by heating in air at 600° C. Zoned patches of chloritic material have formed by crystallization of the late stage magmatic fluid, modified in composition by reactions with olivine and pyroxene.
Xanthiosite and aerugite
Authors: Davis R. J. , Hey M. H. , Kingsbury A. W. G. 
Published: December 2006

SummaryTwo nickel arsenates from South Terras mine, St. Stephen-in-Brannell, Cornwall, have been shown to be identical with the minerals xanthiosite and aerugite, described by C. Bergemann in 1858, and with two synthetic products described by J. B. Taylor and R. D. Heyding (1958). Xanthiosite is pure golden-yellow, monoclinic, with a 10·174, b 9·548, c 5·766 Å, β 92° 58½′, space group P21/a; with D154=5·42±0·10, the unit cell contains 4[Ni3(AsO4)2] (Dcalc 5·388±0·003). Aerugite is deep blue-green, monoclinic, with a 10·29, b 5·95, c 9·79 Å, β 110° 19′, space-group C2, Cm, or C2/m; the ideal unit cell formula is 2[Ni9As3O16], with one-sixth of the arsenic trivalent; the natural mineral has a lower Ni:As ratio, around 2·6. Both xanthiosite and aerugite are minerals new to Britain.
Mineralogy of certain pyrite concretions from Israel and their alteration products
Authors: Sass E. , Nathan Y. , Nissenbaum A. 
Published: December 2006

SummaryPyrite concretions from an arid area of Southern Israel are described. The alteration products include alunite, gypsum, jarosite, baryte, celestine, goethite, hematite, sulphur, and sideronatrite. Sideronatrite is described in detail. The pyrite alteration is considered to be recent and the sideronatrite is preserved owing to climatic aridity. The puzzling appearance of sulphur is tentatively explained by microbiological reduction of the sulphates.
Calciostrontianite in the basal Purbeck beds of Durlston Head, Dorset
Authors: Salter D. L. , West Ian M. 
Published: December 2006

SummaryA spherulitic mineral occurring as veins and nodules in celestine-bearing secondary limestones in the Lower Purbeck Beds at Durlston Head, Swanage, Dorset, is identified as calciostrontianite, a mineralnot previously recorded from Britain. Textural relationships indicate that it was formed from the alteration of celestine and was in part converted back into celestine. The calciostrontianite originated as an epigenetic mineral during the tectonic movement that gave rise to the Broken Beds.
An occurrence of phlogopite and its transformation to vermiculite by weathering
Authors: Smith Aitken W. W. 
Published: December 2006

SummaryThe characteristics of a phlogopite and its weathering product, vermiculite, have been studied by X-ray, infra-red, electron-microscope, and chemical methods. Inclusions within these minerals have been identified as thin films rich in iron oxide (which impart a schiller effect), spinel (which may exist in a preferred orientation), and serpentine. The orientation relationship between the fresh mica and its weathering product has been established by single-crystal methods. The mechanism of transformation from a 1-layer to a 2-layer polytype is discussed.
An electron-microscope study of peristerite plagioclases
Authors: Fleet S. G. , Ribbe P. H. 
Published: December 2006

SummaryPlagioclase feldspars in the peristerite range An2-An17 have been investigated by transmission electron-microscopy and electron diffraction. All except the more anorthite-rich specimens were found to be unmixed into albite and oligoclase lamellae, between a few hundred and several thousand Å thick and approximately parallel to . A discussion is given of the part played by these lamellae when optical schiller is exhibited; and the effect of heat treatment on the lamellar structure and optical schiller is described.
Enhanced production of magnesium silicates from strained magnesia
Authors: Bush W. F. , Williamson W. O. 
Published: December 2006

SummaryMechanically strained, in contrast to annealed, MgO produced greater yields of forsterite and protoenstatite by solid-state reaction with a quartz–cristobalite mixture at 1200–1400° C. The specific surfaces of the strained and of the annealed MgO were similar. The strained MgO was more hygroscopic and similarity of the surface free energies was thus unlikely. The difference in the amounts of silicates produced from the two types of MgO decreased as the temperatures of synthesis increased. This was ascribed to loss of strain energy by unavoidable annealing before and after these temperatures had been reached.Similar results were obtained when hydrated silica was substituted for the quartz-eristobalite mixture, but more forsterite was produced.
The crystal structure of sinhalite
Authors: Fang J. H. , Newnham R. E. 
Published: December 2006

SummaryThe Ceylonese gemstone sinhalite, AlMgBO4, is isomorphous with olivine and chrysoberyl. Aluminium and magnesium are oetahedrally coordinated and boron occupies slightly distorted tetrahedra. Because of size differences, the smaller Al ion can be assigned to the inversion symmetry sites, with Mg in mirror plane positions. Least-squares refinement based on single crystal X-ray data gave an accurate set of atomic coordinates with mean interatomic distances: Al-O 1·90, Mg-O 2·10, B-O 1·49 Å.
Italian meteorites
Authors: Baldanza Bartolomeo 
Published: December 2006

SummaryIn an attempt to assemble together the sparse information regarding the eighty meteorites recorded as having fallen in Italy, tables have been prepared dealing respectively with chronology, name and generalities, synonymy, and literature, together with a distribution map. They are intended not only to help correct identification of pieces widespread in museums or private collections, but also to begin a labelling unification process, in order to avoid confusion arising from a wide variety of synonyms.
A meteorite of unique type from Western Australia: The Mount Egerton stony-iron
Authors: McCall G. J. H. 
Published: December 2006

SummaryA unique meteorite, the existence of which has been known since 1941 but which had been lost, has now been relocated in the form of fragments in two separate collections. Though material available is limited to small fragments, it is sufficient to reveal the principal characteristics of the parent mass, which was a variable body composed of stony material not dissimilar from that of the unbrecciated enstatite-achondrite of Shallowater, Texas, U.S.A., and nickel-iron not dissimilar from the ‘pseudo-octahedrite’ of Horse Creek, Colorado, U.S.A. There is evidence suggesting that it was a stony-iron of a hitherto unrecorded type, and that silicate material predominated.
Pandaite from the Mrima Hill niobium deposit (Kenya)
Authors: Harris P. M. 
Published: December 2006

SummaryA hydrated barium pyrochlore (pandaite) has been found at Mrima Hill (Kenya) in a residuum consisting mainly of goethite/limonite and gorceixite. The pandaite occurs as pale yellow or white octahedral crystals, which have a micro-crystalline interior. It is isotropic, the refractive index varies from 2·07 to 2·11. The calculated specific gravity is 4·07, and the unit cell dimension is 10·59 Å. After deduction of impurities the following formula was obtained (Na0·03 K0·02 Mg0·05 Ca0·09 Ba0·36 Ln0·05 Th0·01 Pb0·004) (Ti0·21 Nb1·78 Ta0·01) (H2O)1·64 O5·52.Comparison of the calculated formula, essentially A0·614B2 (H2O)1·64 O5·52 with the ideal pyrochlore formula A2B2O6F indicates important deficiencies in the structure. Differential thermal analysis shows a large endothermic peak at 340° C and moderate exothermic peaks at 480 and 780° C. In its physical, chemical, X-ray, and thermal properties the Mrima pandaite is similar to pandaites described from other localities.The nature of the alteration of primary pyrochlore to pandaite has been studied using an electron probe.
The thermal decomposition of miscellaneous crocidolites
Authors: Hodgson A. A. 
Published: December 2006

SummarySixteen samples of crocidolite asbestos from weathered zones in mines in Cape Province, Transvaal, Western Australia, and Bolivia have been studied by thermal analysis methods and their characteristics are compared with those of fresh crocidolite from Koegas-Westerberg given by Hodgson, Freeman, and Taylor (1965). New chemical analyses of these samples are reported.The effect of natural weathering on crocidolite tends to a removal of ¼ of the OH groups and an adjustment of the Fe2+/Fe3+ ratio to unity, but there are only minor changes in the physical characteristics of the fibre. The d.t.a. pattern of decomposition is not affected by weathering, but the endothermic peak corresponding to final decomposition is moved to higher temperatures as the Mg content of crocidolite increases. Mg-blocking of this decomposition is considered to be more important than Mg-blocking of the oxidation reaction at 400–450° C, suggested by Addison et al. (1962).D.t.a. and other evidence shows that the Transvaal crocidolite contains intergrown amosite fibres, and suggests that the Bolivian crocidolite is admixed with anthophyllite.