bluuebunny/crossref_metadata_2025_split huggingface dataset:
The iron-titanium oxides of some Dunedin (New Zealand) lavas, in relation to their palaeomagnetic and thermomagnetic character (with an appendix on associated chromiferous spinel)
Authors: Wright J. B. 
Published: December 2006

SummaryEarlier palaeomagnetic studies on the Dunedin volcano showed that a portion of the sequence is reversely or anomalously magnetized. Some of the rocks used for palaeomagnetic study were subsequently classified into groups according to their thermomagnetic behaviour (unpublished work).Cell dimensions and Curie-point curves have been measured for oxides separated from representative rocks of each group. The oxides are mostly homogeneous titanomagnetites containing between 40 and 55 mol. % of ulvöspinel, with a generally small degree of late low-temperature alteration. X-ray and thermomagnetic data also suggest that there was some early oxidation to titanomaghemite, probably during cooling.The thermomagnetic behaviour of rocks classified in the different groups is attributed to variable oxidation of the titanomagnetite during thermomagnetic treatment. The high Curie points of rocks used for palaeomagnetic studies may often be due merely to oxidation of titaniferous magnetite and not to nearly pure primary Fe3O4. Since there is insufficient oxidation in the lavas examined for any currently accepted self-reversal process to have been operative, the reversely magnetized part of the Dunedin sequence was probably erupted during a reversed polarity epoch, possibly between about 13 and 11 million years ago.The basanitic lavas contain minor amounts of chromiferous spinel, as inclusions in silicate phenocrysts and as cores to separate microphyric titanomagnetite; its significance is briefly discussed.
The crystal structures of sjögrenite and pyroaurite
Authors: Ingram L. , Taylor H. F. W. 
Published: December 2006

SummaryThe crystal structures of sjögrenite and pyroaurite, two stacking modifications of approximate composition Mg6Fe2(OH)16(CO3).4H2O, have been determined by X-ray diffraction using three-dimensional methods. Sjögrenite is hexagonal, with a 3·13, c 15·66 Å, space group P63/mmc , Z = ¼; pyroaurite is rhombohedral, with aH 3·13, cH 23·49 Å, space group R3̄m or R3m, Z = ⅜. Both structures are based on brucite-like layers, with magnesium and iron distributed among the octahedral positions. The cations appear to be largely disordered, although ordered regions may occur in some crystals. Between the brucite-like layers are the water molecules and carbonate groups. These are statistically arranged, with their oxygen atoms distributed among a larger number of possible sites.
The crystal structure of epistilbite
Authors: Perrotta A. J. 
Published: December 2006

SummaryThe crystal structure of epistilbite ((Ca2·59Na1·06K0·10) (Al6·29Si17·71O48).15·74H2O; C2/m; a = 9·08, b = 17·74, c = 10·25±0·01 Å; β = 124·54±0·05°) was determined by 3-D least-squares methods. The alumino-silicate framework is composed of 4-, 5-, and 8-membered rings of tetrahedra. There are two sets of intersecting channels each defined by 8-membered rings. The (Ca, Na) atoms in the channels are in contact with seven water molecules and two oxygen atoms giving a coordination of nine at a cut-off distance of 2·77 Å. The average tetrahedral distance is lower than for anhydrous framework alumino-silicates but consistent with some other zeolite structures. Partial Al-Si ordering exists with one tetrahedron occupied preferentially by aluminum. This tetrahedron contains the two oxygen atoms that are coordinated with the (Ca, Na) atom.
Myrmekite and myrmekite-like intergrowths
Authors: Shelley D. 
Published: December 2006

SummaryMyrmekite-like intergrowths in the Lewisian gneiss and the igneous complex of Loch Borolan are described. The intergrowths are of diverse mineral composition but have many features in common with myrmekite and it is shown that they result from the constriction of a previously existing mineral during the growth, in the solid state, of the host mineral. More than one stage of intergrowth is often found and these stages can be correlated with geological events.
Some topaz-, sillimanite-, and kyanite-bearing rocks from Tanzania
Authors: Kempe D. R. C. 
Published: December 2006

SummarySome sillimanite-kyanite quartzites, which may grade into sillimanite-kyanite topazfels, from NE. Tanzania are described. In view of the suggestion that a solid-solution series might exist between topaz and sillimanite, the cell dimensions and some optical properties of both minerals were investigated. No abnormal results, suggesting solid solution, were obtained and the coexistence of topaz, sillimanite, and kyanite is ascribed to particular physico-chemical conditions.
Structural similarities of some secondary lead minerals
Authors: Fanfani L. , Zanazzi P. F. 
Published: December 2006

SummarySome structural analogies found in tsumebite, vauquelinite, fornacite, and brackebuschite make it possible to place these secondary lead minerals in the same series with general formula Pb2MeII(Z)(XO4)(YO4), where MeII is a bivalent cation as Cu2+ or Mn2+, Z is the hydroxyl group or the water molecule, X is S, Cr, or V, and Y is P, As, or V. Some crystallochemical considerations are developed in order to explain how the replacement of these elements affects the crystal structure in these substances.
Apatite compositions and liquidus phase relationships on the join Ca(OH)2-CaF2-Ca3(PO4)2H2O from 250 to 4000 bars
Authors: Biggar G. M. 
Published: December 2006

SummaryPhase equilibria involving solids, liquids, and vapours on the join Ca(OH)2-CaF2-Ca3(PO4)2-H2O were determined at 1000 bars. The temperatures and liquid compositions (weight %) of the isobaric invariant reactions encountered were: portlandite+fluorite → liquid, 687° C, 70 % Ca(OH)230 % CaF2; portlandite+fluorite+vapour → liquid, 675° C, 69% Ca(OH)226 % CaF25 % H2O; portlandite+fluorite+apatite → liquid, 675°C 73 % Ca(OH)224 % CaF23 % Ca3(PO4)2; portlandite+fluorite+apatite+vapour → liquid, 665° C, 70 % Ca(OH)222 % CaF23 % Ca3(PO4)2, 5 % H2O. The temperatures of these reactions were determined from over 400 experimental runs at selected pressures from 250 to 4000 bars. The composition of the apatite involved in the last two reactions was 60 % hydroxyapatite 40 % fluorapatite and in subsolidus regions in the presence of water, fluorapatite did not crystallize but fluorhydroxyapatite solid solutions coexisted with vapours containing up to 2·5 % hydrogen fuoride. These observations suggest that hydroxyapatite is more stable than fluorapatite at elevated temperatures and pressures and would be the composition expected to crystallize under igneous and metamorphic conditions.
On conventional calculations of amphibole formulae from chemical analyses with inaccurate H2O(+) and F determinations
Authors: Borg I. Y. 
Published: December 2006

SummaryFor chemical analyses with inaccurately reported H2O(+) or F, calculation of an amphibole formula on the basis of 23(O) after discarding the reported H2O(+) is in most cases as unsatisfactory as a standard calculation including H2O(+) based on 24(O, OH, F). The sum of the cations in X, Y, and Z groups most closely approaches theoretical values in a 23(O) calculation, but only by virtue of compensating and compounded errors of opposite sign. Realization of the ideal formula by either method without additional data is not an infallible criterion of accuracy of the analysis or the correct site occupation. These conclusions stem from the observation that although H2O(+) may be incorrect, most analyses add up to 100.00 or greater; thus compensating errors in metallic oxides are implicit.
Oriented lamellae in the Gibeon meteorite
Authors: Frost Michael J. 
Published: December 2006

SummaryA re-examination of twelve specimens of the Gibeon meteorite has established that the meteorite is basically an octahedrite but has, in several irons of the meteorite, lamellae of kamacite of early origin parallel to the cube. Lamellae containing daubréelite, predating twinning and kamacite exsolution, are common parallel to the cube and rare parallel to the octahedron. A survey of other features failed to suggest any definitely correlated with the anomalous kamacite lamellae.
The morphology of cerussite
Authors: Seager A. F. 
Published: December 2006

SummaryThe observed order of importance of the forms of cerussite has been determined by the methods introduced by Donnay and Harker, used in a modified form. The space group derived by morphological analysis is Pmcn, as determined by X-ray diffraction. For the more common forms good agreement is found between the observed and theoretical orders of importance. The rank distribution of the more important forms is given.
Minor elements in some rocks and minerals of the Rakha mines area, Singhbhum, India
Authors: Bhattacherjee S. B. , Ghosh A. K. , Bhattacherjee L. , Bhattacherjee Santi 
Published: December 2006

SummaryThe minor elements present in some rocks and minerals of the Rakha mines area, Singhbhum district, Bihar, India, have been determined by X-ray fluorescence spectroscopy. Geological and geochemical studies in different parts of this shear zone already favour a hydrothermal origin. Some of the minor elements concentrated in the sulphide ores are found in lower concentration in the epidiorite and the chlorite-mica schist; these are, however, present in abundance in the soda-granites that are closely associated in space to the east and west of the Rakha mines area. A genetic link between sulphide ores and soda-granite may be predicted although the sulphides in the Rakha mines area are not directly associated with the soda-granite.
A study of calcium hexaluminate
Authors: Buist D. S. 
Published: December 2006

SummaryCalcium hexaluminate has recently been confirmed as a stable phase occurring within the system CaO-Al2O3. In the present investigation, this aluminate has been synthesized from the constituent oxides and its X-ray, optical, and physical (microhardness and reflectivity) properties determined. Similar data have also been obtained on the ferrian phase from the immediate hot-face zone of high-alumina bricks that had been in service in electric arc furnace roofs. An electron-probe microanalysis study revealed that between 12 and 13 % atomic replacement of Al by Fe had occurred in this ferrian calcium hexaluminate. The melting behaviour of the pure compound has been studied by firing pellets in a specially-constructed vacuum furnace. Results show the incongruent melting point to be 1870°C (±10° C), while the liquidus temperature is 1970° C (±10° C). These points were determined by examining polished sections of compacts heated within the range 1820 to 2000° C. A revised phase diagram of the high-alumina portion of the system CaO-Al2O2 is presented.
Mackinawite, pentlandite, and native copper from the Newport pallasite
Authors: Buseck Peter R. 
Published: December 2006

SummaryThese minerals indicate strongly reducing conditions as well as extremely low sulphur fugacities within the Newport pallasite. They all formed at low temperatures (upper limit 580° C) and in the solid state. This is the first reported occurrence of mackinawite and pentlandite from a pallasitic meteorite; Cu is known from only one other pallasite. Microprobe analyses of a large Cu grain indicate its composition as 98·6 ± 0·5 %, Ni 2·0 ± 0·5, Fe below the limit of detection (∼0.3).
The Bencubbin meteorite: further details, including microscopic character of host material and two chondrite enclaves
Authors: McCall G. J. H. 
Published: December 2006

SummaryThe Bencubbin meteorite and some of its enclaves have been studied in thin section under transmitted light: supporting X-ray diffraction and chemical data have been supplied by the Smithsonian Institution, Washington. These results show the host material to consist of clinoenstatite and a little olivine (both nearly pure magnesian varieties) set in an opaque (cryptocrystalline ?) base, which is, in turn, enclosed in a mesh-work of nickel-iron, of composition equivalent to a hexa-hedrite. Two enclaves are revealed as: an atypical olivine-hypersthene chondrite (in the mode, the olivine is Fa19, and pigeonite takes the place of orthopyroxene, but the chemical analysis is typical except for a small but appreciable carbon content); and an enstatite chondrite displaying crudely formed chondrules (chemically typical, with a small but appreciable carbon content).The chondrite enclaves are not recrystallized: though Lovering has referred to the first as ‘thermally metamorphosed’, and both are dark coloured, there seems to be little evidence of the effect of the metallic host, which must surely have been molten, on the chondrite enclaves, which seem to have been able to survive in this environment without mineralogical or textural modification.Lovering has stressed the importance of this meteorite in its bearing on meteorite provenance and genesis, and the further implications of this present study are discussed briefly.
An occurrence of todorokite in the deuteric stage of a basalt
Authors: Lawrence L. J. , Bayliss P. , Tonkin Paul 
Published: December 2006

SummaryAn occurrence of todorokite having a formula is recorded from Ardglen, 150 miles N.N.W. of Sydney, New South Wales. The composition of Ardglen todorokite is somewhat simpler than previously recorded occurrences, most of which were in manganese and manganese—base-metal ore deposits. The simpler composition is explained in terms of its occurrence as a late deuteric mineral associated with manganocalcite and zeolites in an altered Tertiary basalt. The manganese is believed to have been derived from the deuteric alteration of the augite of the basalt.
The thermal expansion of the sodalite group of minerals
Authors: Taylor D. 
Published: December 2006

SummaryThermal expansion data up to 920° C by powder X-ray diffraction methods are presented for four noseans, five haüynes, and one sodalite. The rate of thermal expansion is at first high and increases with temperature; this is interpreted as due to the untwisting of the partially collapsed framework. Above a certain temperature (which depends on the mineral and its composition) the rate of thermal expansion is much lower and is linear with temperature; this corresponds to the rate of thermal expansion of the more fully expanded framework. Sodalite does not show this second stage below 920° C. The thermal expansion behaviour of other framework silicates is interpreted in analogy to that of the sodalite group.
Calzirtite and the mineralogy of residual soils from the Bukusu carbonatite complex, south-eastern Uganda
Authors: Baldock J. W. 
Published: December 2006

SummaryCalzirtite, essentially CaTiZr3O9, has been identified in residual soils from the Bukusu carbonatite complex in Uganda. A satisfactory ultrasonic technique was developed for cleaning the samples prior to studying their mineralogy. Other heavy minerals present include ilmenite, perovskite, melanite, apatite, zircon, and baddeleyite. The properties and composition of calzirtite are compared with the available data from occurrences in the U.S.S.R. The mineral has a metasomatic paragenesis and probably indicates the presence of carbonatized rocks at depth.
The oxidation of Bolivian crocidolite
Authors: Addison W. E. , White A. D. 
Published: December 2006

SummaryA hypothesis has previously been advanced to account for the termination of the dehydrogenation process for the oxidation of South African crocidolite : it was postulated that the presence of magnesium ions would block the electronic migration required for complete oxidation of iron(II) in the temperature range 400° to 500° C. In view of criticism of the validity of the evidence for this hypothesis, new data for the oxidation of Bolivian crocidolite, which has a much higher magnesium content than the South African material, is presented; this is more satisfactory evidence of the validity of the hypothesis.
Orientation of the boundaries of out-of-step domains in anorthite
Authors: Ribbe Paul H. , Colville Alan A. 
Published: December 2006

SummaryThe orientation of the boundaries of out-of-step domains in ‘transitional’ anorthite has been deduced from the direction of elongation of the diffuse X-ray reflections h + h + l = 2n + 1 in selected precession photographs. The reflections are elongated normal to which is in the zone and contains the body-centring vector (a+b−c)/2. The structure is presumed to be perfect parallel to . Atoms in essentially identical, primitive anorthite-like domains are related across the out-of-step domain boundaries by body-centring vectors. Increasing diffuseness of the h + k + l = 2n + 1 reflections indicates progressively smaller domains (more frequent domain boundaries), and when thesereflections disappear, the structure has become body-centred on the average.
Compact chlorite associated with lizardite from New South Wales, Australia
Authors: Golding H. G. , Bayliss P. 
Published: December 2006

SummarySegregations of compact chlorite from ultramafic belts in New South Wales have been examined using chemical, X-ray, differential thermal, and electronprobe techniques. The chlorites vary from pennine to sheridanite. Some segregations occupy the central zone in metasomatic sequences of altered chromite, chlorite, and lizardite; but others may have formed at junctions of serpentinite and rodingite.
Perryite in the Kota-Kota and South Oman enstatite chondrites
Authors: Reed S. J. B. 
Published: December 2006

SummaryElectron-microprobe scanning pictures and quantitative analyses of the nickel silicide perryite in the Kota-Kota and South Oman enstatite chondrites are given. Comparative data for the narrow perryite lamellae in the Horse Creek iron meteorite are included. Perryite in these meteorites lies within the limits 75–81% Ni, 3–7 % Fe, 12–15 % Si, 2–5 % P.
Onoratoite, a new antimony oxychloride, from Cetine di Cotorniano, Rosia (Siena, Italy)
Authors: Belluomini G. , Fornaseri M. , Nicoletti M. 
Published: December 2006

SummaryOnoratoite, a new antimony oxychloride Sb8O11Cl2 from the antimony mines of Cetine di Cotorniano, Rosia (Siena, Italy), is triclinic with lattice constants a 18·92, b 4·03, c 10·31 Å, α ≃ γ ≃ 90°, β 110°. Density 5·3 meas., 5·49 calc. The needle-like crystals are elongated on [010] and show as prominent form {001}. Other forms present are {100}, {201}, {401}, {412}.The new mineral is optically biaxial negative, extinction angle small and variable from 0° to 14°. Orientation β:[100] ca. 8°; α:[001] ca. 12°; γ:[010] 0 to 14°. Refractive indices are 2·26 > γ > 2·23, 2·23 > β > 2·18. Birefringence γ-β 0·024 (meas.).The stability field of onoratoite has been investigated by systematic thermo-gravimetric and differential thermal analysis of antimony oxychlorides and by a direct study of equilibrium relationships in the system SbCl3-Sb2O3-HCl-H2O. The probable mechanism of formation of onoratoite is discussed.Onoratoite is named in honour of the Italian mineralogist Ettore Onorato.
An experimental study of ordering in sodium-rich alkali feldspars
Authors: Parsons Ian 
Published: December 2006

SummaryVariations in the value of 2θ131 – 2θ13̄1 of two anorthoclase feldspars of compositions Ab95Or5 and Ab90Or10 were investigated by hydrothermal crystallization of gels for long periods in the temperature range 500–950 °C, at water vapour pressures up to 15 000 lb/in.2. The results are compared to those obtained by MacKenzie (1957) for pure albite. It is shown that the variation in 2θ131 – 2θ13̄1 is largely the result of Al-Si order-disorder and that at 700 °C and above the magnitude of the variation in the anorthoclases suggests that the degree of order is like that in albite, but at lower temperatures, particularly below 600 °C, the variation is less, and the anorthoclases are less ordered than albite at the same temperatures. At 600 °C and above the rate of attainment of equilibrium is the same for all three compositions. Below 600 °C Ab95Or5 behaves differently to albite. At low temperatures the equilibrium degree of Al-Si order in mixed Na-K feldspars is a function of composition as well as of temperature of crystallization.
On the electrolysis of molten basalt
Authors: Oppenheim M. J. 
Published: December 2006

SummaryThe effects to be expected from the interaction of possible electric currents at depth with bodies of basaltic magma have been investigated experimentally. Trough-shaped molten specimens were produced in the surface of basalt blocks by heating from above ; the melts were electrolysed and the products analysed chemically.Si, Al, Ti, P, Fe2+, and probably Fe3+are concentrated towards the anode, apparently in the form of drifting lattice remnants; oxygen gas is liberated. Na, K, Ca, Mn, and Mg ions concentrate towards the cathode.Relatively to basalt, the cathodic product is an alkaline and femic rock with normative nepheline and a more acid plagioclase. The anodic rock is distinctly calc-alkaline and salic, with normative quartz and a plagioclase that is more basic. The precise ‘rock-type’ developed depends on the amount of electricity passed, but the trends are distinct. In that increasing basicity and alkalinity (cathodic rocks) are accompanied by both increasing Na/K and Mg/(Fe2++ Fe3+) ratios (which ratios decrease with decreasing basicity and alkalinity) the electrolytic series developed from a basalt magma appears to have few counterparts among natural rocks.
Cell dimensions of olivine
Authors: Louisnathan S. J. , Smith J. V. 
Published: December 2006

SummaryCell dimensions obtained from X-ray powder photographs of twenty-four natural olivines and one synthetic forsterite have been related to the cation contents by a new statistical procedure developed by M. H. Hey. Unlike conventional statistical analysis, which assumes error only in one parameter, this procedure simultaneously considers the estimated errors in all variables.Linear terms in Ca, Mn, Mg (or Fe(≡ 1-Mg-Ca-Mn)) satisfactorily account for the cell dimensions, and there was no need to invoke a term in Mg2. Since there are three cell dimensions and three chemical unknowns, it is theoretically possible to estimate the major cations in olivine just from the cell dimensions. However, the coefficients for Mn and Fe are so similar and the ranges of Ca and Mn are so small that the technique would be impractical.Data for ideal (Mg,Fe) olivines were estimated by adjusting the cell dimensions by linear extrapolation from the cell dimensions of tephroite and monticellite. A simple chemical term was sufficient to account for each cell dimension. The linear relation between cell volume and Mg is consistent with the complete disorder of Mg and Fe revealed by parallel single-crystal X-ray studies.The cell dimensions of a synthetic fayalite deviate significantly from those of natural fayalites after correction for the effects of Ca and Mn substitution in the latter: some structural or chemical difference, probably involving ferric iron, is indicated.No superstructure lines have been found, in contradiction to Eliséev's data.
The metallographic structure of the iron meteorites Arltunga, Kopjes ,Vlei, Murnpeowie, Braunau, and Rancho de la Pila
Authors: Axon H. J. 
Published: December 2006

SummaryFrom a metallographic examination it is suggested that Rancho de la Pila is a shock-hardened octahedrite; Murnpeowie is a cosmically reheated meteorite of unusual composition; Kopjes Vlei may have been produced by the reheating of a shock-hardened hexahedrite either cosmically or on earth; Braunau shows signs of preterrestrial reheating but Arltunga is a nickel-rich ataxite with no signs of metabolic alteration.
Mineralogical note on the chrome-chlorite (kämmererite) and chrome-garnet (uvarovite) from the chromite deposits of Kalrangi, Orissa, India
Authors: Chakraborty K. L. 
Published: December 2006

SummaryThe geological set-up, chemical composition, physical and optical properties, and X-ray data of one sample of chrome-chlorite (kämmererite) and of a chrome-garnet (uvarovite) from Kalrangi chromite mines, Orissa, India, are presented here. Chrome-bearing solution contributed in the formation of both the minerals in the hydrothermal stage. It is suggested that the garnet is an intermediary form between uvarovite and pyrope.