bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mineralogy of metamorphosed basic rocks from the Willyama Complex, Broken Hill district, New South Wales. Part I. Hornblendes
Authors: Binns R. A. 
Published: December 2006

SummaryThe typical hornblendes of metabasic rocks in the Willyama Complex change from bluish-green to deeply coloured brownish varieties with increase in metamorphic grade. Chemical analyses and optical properties of 23 representative hornblendes are interpreted as showing this colour change to reflect steady increase in titanium content of the hornblendes with increase in grade. High-grade hornblendes also differ from those of lower grade in that tetrahedral aluminium in the Z sites is balanced to an increased extent by alkalis entering the A site rather than by octahedral aluminium entering the Y site. Comparison between theoretical and measured densities of Willyama hornblendes suggest that a calculation based on 23 oxygen anion provides closer approximations than a 24 (O, OH, F) calculation to their structural formulae.
Topotaxy in the system MnO-O-H2O: groutite–ramsdellite–pyrolusite
Authors: Dent Glasser L. S. , Smith Ian B. 
Published: December 2006

SummaryX-ray and thermal studies in the system MnO-O-H2O show that the transformations groutite(α-MnOOH)-ramsdellite(MnO2)-pyrolusite(MnO2) are topotactic, with the a, b, and c directions of all three corresponding. The reactions proceed by migration of manganese atoms and, where appropriate, protons. Pure single crystals of ramsdellite could not be prepared by heating groutite, even though the two structures are very similar.
Optics of hexagonal pyrrhotine (~Fe9S10)
Authors: von Gehlen Kurt , Pillier Horst 
Published: December 2006

SummaryReflectivities of a series of oriented polished sections through a single crystal of pyrrhotine (Fe1−αS) from Trepča, Yugoslavia, were measured by means of a spectral photometer attached to a microscope. This pyrrhotine consists of two phases, namely intermediate pyrrhotine (∼ Fe9S10) and monoclinic pyrrhotine (∼ Fe7S8), which were probably formed by exsolution. The phase relations of pyrrhotine at low temperatures are discussed. Optical data are given for the intermediate pyrrhotine from 440 to 660 mµ. From the reflectivities measured in air and oil against a carborundum standard, values of n, k, and κ were calculated for ω and ε and represented in dispersion curves. Also, sections through the various ‘indicating surfaces’ at 546 mµ are shown. The accuracy of the values, which should be approximately the same for other pyrrhotine phases, is discussed.
Some crystallographic studies in the system CaSOa4-CaSO4.2H2O I. The polymorphism of anhydrous CaSO4
Authors: Gay P. 
Published: December 2006

SummaryThe existence and relationships of the polymorphs of CaSO4have been studied by X-ray methods. Only two distinct phases are found: no crystallographic evidence is available to support the suggestion that theγ-CaSO4structure can have two forms, and it is shown that most previous data on the existence of the high temperatureα-CaSO4polymorphs are likely to be due to decomposition of the sulphate.Some observations on theγtoβ-CaSO4transformation are reported. The structural implications of these results and their relevance to the nature of the transformation are discussed.
Some crystallographic studies in the system CaSO4–CaSOa4.2H2O II. The hydrous forms
Authors: Gay P. 
Published: December 2006

SummaryThe existence and relationships of hydrated forms both to one another and to anhydrous CaSO4have been studied by X-ray methods. Detailed study of the hemi-hydrate reveals its true cell to be monoclinic and does not confirm the previously suggested polymorphism.Dehydration studies of the dihydrate and hemi-hydrate are reported; cyclic dehydration and hydration of single crystals of the latter show a variable temperature interval between the formation ofγ-CaSO4and the reconstitution of the hemihydrate at approximately constant humidity. An explanation of this behaviour is offered, and the structural implications of the results of the dehydration studies are discussed.
Potash-trachytes and ultra-potassic rocks associated with the carbonatite complex of the Toror Hills, Uganda
Authors: Sutherland D. S. 
Published: December 2006

SummaryRocks containing a high percentage of potash feldspar are described for the first time from the Toror Hills in the Karamoja district of eastern Uganda. They include feldspathic fenites, intrusive feldspathic fenite-breccias, potashtrachytes, and orthoclasites. Petrographic data and chemical analyses show the close similarity in composition of these rocks despite their widely differing textures and modes of occurrence. The potash metasomatism associated with the emplacement of carbonatite, and the subsequent mobilization of these feldspathic fenites are compared with similar phenomena observed at other carbonatite centres. The problem of the mechanism of mobilization is discussed.
Tin-containing andradite from Plavno mine in the Krušné Hory Mts., Czechoslovakia
Authors: Dadák V. , Novák F. 
Published: December 2006

SummaryStannian andradite occurs with pyroxene and carbonates, with blende and pyrite as accessories in a skarn deposit in the Plavno mine, Krušné Hory Mts., NW. Bohemia. The green crystals are rhombic dodecahedra up to 3 cm in size. Sp. gr. 3·78; n 1·879; a 12·079±0·002 Å. Quantitative chemical and spectrographic analyses are given; the composition is (Ca2·96Mg0·04Mn0·02)3·02 (Si2·95Sn0·04)2·99O12. The content of tin (SnO2 1·07 %) is isomorphously bound in the lattice, and according to crystallochemical calculations the entrance of tin into the garnet lattice is most probably due to substitution of The presence of tin in the andradite shows that this element was already present in the metasomatic solutions during the process of skarnization.
Garnets from the Eilat area, southern Israel
Authors: Nathan Y. , Katz A. , Eyal M. 
Published: December 2006

SummaryGarnets from twenty-eight pegmatites, schists, and gneisses from the crystalline massif of Eilat have been examined. Refractive index, unit-cell edge, MnO and FeO content were determined in 19 samples. Three chemical analyses are given. The garnets fall into two distinct groups, the pegmatite garnets (spessartine-rich, almandine to spessartine) and metamorphic garnets (nearly pure almandine). Garnets occurring in pegmatite-like granitoid veins cutting through the schists are shown to belong to the second (metamorphic) group. The pegmatite garnets again fall into two groups of different spessartine content.
Feldspars and pryoxenes from the charnockite aeries of Visakhapatnam area, Andhra Pradesh, India
Authors: Murty M. S. 
Published: December 2006

SummaryA twin-law study of the plagioclase indicated metamorphic origin of the charnockites and volcanic origin of the basic members of the charnockite series. The original volcanic products have been influenced by the later metamorphism, resulting in the various basic members. The twinning in the plagioclase is considered to be primary. The perthite in the charnockite is of orthoclase variety and indicates a higher temperature of formation than the charnockites of other areas containing microcline. The orthopyroxene in the charnockite series is hypersthene and the clinopyroxene is sahlite. Hypersthene is inferred to have formed at the expense of sahlite, hornblende, biotite, and garnet.
Determination of the optic axes and 2V: electronic computation from extinction data
Authors: Joel N. 
Published: December 2006

SummaryExtinction readings are taken, on a polarizing microscope, for several wave-fronts in a biaxial crystal (more than four wave-fronts are required). With these extinction data, the machine then calculates the directions of the two optic axes and of the three principal axes of the indicatrix, as well as the value of the optic axial angle 2V, using a least-squares successive approximation technique. The programme was written for an IBM 1620 computer.
An improved water cell for the Emmons double-variation procedure
Authors: Tarney J. , Lacy E. D. 
Published: December 2006

SummaryAn improved water cell for the Universal Stage is described for use in the Emmons double-variation procedure. The cell provides an increased heat flow to the mineral grains, and the technique of orientating and retaining the grains in the centre of the field of view is greatly simplified.
The thermal decomposition of amosite
Authors: Hodgson A. A. , Freeman A. G. , Taylor H. F. W. 
Published: December 2006

SummaryWhen amosite (fibrous grunerite, Fe5·5Mg1·5Si8O22(OH)2), is heated in argon or nitrogen, physically combined water is lost up to 500–700° C. Above 500° C (static) or 700° C (dynamic), dehydroxylation occurs endothermically, giving a pyroxene as the main product. Under dynamic heating conditions, part of the hydroxyl water is lost as hydrogen, with concurrent oxidation of the iron. At about 1000° C the pyroxene is decomposed to olivine and cristobalite; at about 1100° C melting begins. In oxygen or air, physically combined water is again lost below 500–700° C. At 350–1200° C a sequence of overlapping dehydrogenation, oxygen absorption, and dehydroxylation reactions occurs, which gives rise to a broad exotherm on the d.t.a. curve. The main products (for static heating conditions) are an oxyamphibole at 350–800° C, and a spinel, hematite, a pyroxene, and X-ray amorphous material at 800–1100° C. Silica crystallizes as cristobalite at 1100–1350° C, and as tridymite at 1450° C. Most of the products in either neutral or oxidizing atmospheres are formed topotactically. The mechanisms and rates of the reactions are discussed, and the problem of determining the chemically combined water in amosite and other minerals of similar composition is considered.
Stability and relations of the Al-Fe epidotes
Authors: Strens R. G. J. 
Published: December 2006

SummaryThe various (P, T) stability fields of iron-free zoisite have been deduced for systems containing excess silica and water with Ca : Al ratios ranging from 1 : 2 (anorthite) to 3:2 (grossular). Zoisite is a possible phase in all systems with Ca:Al lower than 3:2, attaining its maximum stability at the zoisite (Ca:Al = 2:3) and prehnite (Ca:Al = 2:2) compositions.The consequences of varying the Al : Fe ratio are next examined. Zoisite with 4 % pistacite is stable to 525° at 2 kilobars, compared with ∼585° for clinozoisite and 620 to 630° for epidote (Ps35) at the same pressure. Increasing iron content also stabilizes epidote minerals relative to their low-temperature and high-pressure decomposition products.Examples of natural zoisite-clinozoisite, zoisite-epidote, and clinozoisite-epidote assemblages are described. It is concluded that zoisite-epidote mixtures result from the disproportionation of clinozoisite outside its own stability field, but within those of zoisite and epidote. The assemblage zoisite-clinozoisite is probably not stable, but further evidence is needed on this point. The assemblage clinozoisite-epidote is stable below 550° C, at which temperature the solvus in the Al-Fe series closes.
New material from, and a reconsideration of, the Dalgaranga meteorite and crater, Western Australia
Authors: McCall G. J. H. 
Published: December 2006

SummaryTwo small fragments of unpromising-looking ferruginous material, recovered from inside the Dalgaranga crater, near Mount Magnet, Western Australia, have been sectioned and, while one is largely composed of iron oxides and adds little to the record of this crater, the second fragment is one of the rare, predominantly stony ones reported by Nininger and Huss, and is sufficiently fresh for a thin section to be prepared. As far as is known no thin sections have been described of material from this crater. Microscopic study with transmitted light shows the stony material to be achondritic and to have affinities with the mesosiderites, and, in spite of the low nickel-iron content of this fragment, it seems preferable to regard it as representative of an iron-poor area within a mesosiderite than as true stony meteorite material. Although closely related to the howardites it cannot be classified with any known achondrite type because of the prominent olivine phenocrysts and it bears no resemblance at all to chondritic material. Mineralogical and petrographical details are described and illustrated, and the significance of this new evidence discussed. The origin of the crater is reconsidered.
Plagioclase twins in some mafic gneisses from Broken Hill, Australia
Authors: Vernon R. H. 
Published: December 2006

SummaryPlagioclase in mafic gneisses from Broken Hill, Australia, contains twins that can be divided into two groups on the basis of shape: firstly, lamellar twins that gradually change thickness across a grain or form lenticular terminations; and secondly, simple and lamellar twins that show angular steps in the twin interface or form abrupt, planar terminations. The former are interpreted as mechanical twins, and the latter as growth twins formed by grain growth in the solid state, arguing largely by analogy with twin shapes in experimentally produced aggregates, particularly metals. The only twin laws observed in lenticular twins are albite and pericline, these being of nearly equal abundance. Stepped twins are much less common than lenticular twins, and in rocks without lenticular twins most of the plagioclase is untwinned. Several twin laws occur among the stepped twins, but the albite law is the most common. Simple twins on the albite and albite-carlsbad laws are prominent.
Isotopic ages of the basic charnockite and khondalite from Kondapalli, Andhra Pradesh, India
Authors: Grasty R. L. , Leelanandam C. 
Published: December 2006

SummaryThe isotopic ages of three biotites from the Kondapalli area, Andhra Pradesh, India, have been determined by the 40Ar/40K method. The results (440–524 Myr) indicate that the basic charnockite and khondalite of pre-Cambrian age have been subjected to at least one subsequent metamorphism the age of which must be 440 Myr or younger. The significance of the results is discussed in the light of the available geochronological evidence from Peninsular India.
A continuous, laboratory-size density separator for granular materials
Authors: Jones M. P. 
Published: December 2006

SummaryDetails are given for the construction of a continuous, density separator from standard laboratory glassware and equipment. The separator can treat up to 5 g/min of granular material from 150 to 2000 µ in grain size, and the liquid used is continually recirculated by a simple airlift.
The crystal structure of kalsilite, KAlSiO4
Authors: Perrotta A. J. , Smith J. V. 
Published: December 2006

SummaryA full-matrix, three-dimensional refinement of kalsilite, KAlSi04 (hexagonal, a 5·16, c 8.69 Å, P6a), shows that the silicon and aluminium atoms are ordered. The respective tetrahedral distances of 1·61 and 1·74 Å agree with values of 1·61 and 1·75 Å taken to be typical of framework structures. As in nepheline, an oxygen atom is statistically distributed over three sites displaced 0·25 Å from the ideal position on a triad axis. This decreases the bond angle from 180° to 163° in conformity with observations on some other crystal structures. The potassiumoxygen distances of 2·77, 2·93, and 2·99 Å are consistent with the wide range normally found for this weakly bonded atom.
Crystallography of psilomelane, A3X6Mn8O16
Authors: Mukherjee Bibhuti 
Published: December 2006

SummaryPsilomelane has been redefined from single crystal study to be of orthorhombic symmetry with the space group P222, the dimensions a 9·45, b 13·90, c 5·72 Å, and two molecules of per unit cell, where A represents Ba2+, Mn2+, Al3+, Fe3+, Si4+ etc., and X6 stands for (O,OH)6 with OH about 5. This formula is very closely followed by 14 analyses of psilomelane, and the calculated density agrees fairly well with the observed density. The powder data of psilomelane cannot be indexed with Wadsley's monoclinic cell and the conditions for the space group A2/m, proposed by Wadsley for his crystal, are not satisfied by the indexing. Wadsley's crystal was not psilomelane but probably an altered phase of Vaux's neotype specimen.The electron micrograph of shining platy crystals of psilomelane shows some almost square-faced crystals whereas that of the botryoidal material consists only of particles with irregular edges. The dehydration product of psilomelane shows gradual shrinkage of the orthorhombic cell up to 500° C, marked structural changes at 600° C, and transformation at 800° C to a monoclinic phase, similar to hollandite.
The significance of granophyric and myrmekitic textures in the Lundy Granites
Authors: Shelley D. 
Published: December 2006

SummaryZonal myrmekitic and granophyric intergrowths in plagioclase and K-feldspar phenocrysts are described. There are two such zones in the feldspars of the Late Granite, G2, but only one in the Early Granite, G1. The zonal granophyric intergrowths are the end-product of the replacement of myrmekitic plagioclases by K-feldspar. Transitional stages of this replacement, which took place in the solid state, are represented in numerous examples. The zones of myrmekite, which also represent growth in the solid state, occur between zones of magmatic plagioclase, which is oscillatory-zoned. It is concluded that the granites evolved at depth under the influence of at least three phases of volcanic activity. Each of these phases resulted in the partial melting of the country rocks with subsequent magmatic crystallization, followed further, under the slow cooling conditions, by extensive reaction in the solid state. During each of the final two phases, some of the granite was intruded as a crystal mush to form G1 and G2, in which the phenocrysts retain evidence of their evolution at depth whilst the ground-mass gives evidence of the final magmatic crystallization.
Origin of optical pleochroism in orthopyroxenes
Authors: Burns Roger G. 
Published: December 2006

SummaryThe necessary conditions for optical pleochroism in orthopyroxenes are: ordering of Fe2+ ions, with preferential occupation of M2 positions; presence of small, high-valence cations (Al3+, Fe3+, Ti4+) in M1 positions; replacement of Si by Al; and a sufficient Fe2+ content. These factors favour an intensification of the charge-transfer absorption bands in the ultra-violet that is more marked for the α vibration direction than for β and γ. This leads to absorption in the blue and a red colour in transmitted α-polarized light, while β and γ, remain green.
The use of An and Sr data on plagioclase in a study of basic xenoliths in a gabbroic mass at Hamar, Somalia
Authors: Butler J. R. , Skiba W. 
Published: December 2006

SummaryIn this paper we give data for An and Sr in plagioclase to demonstrate the presence of numerous amphibolite xenoliths within parts of a basic igneous mass where, after initial reconnaissance mapping, none was suspected. The data also show that the concentration of Sr in plagioclase from the margin of some amphibolite xenoliths is appreciably higher than in plagioclase from either the cores of the xenoliths or the enclosing metagabbro even though the modes and An contents of the plagioclase are similar. An explanation is offered, which implies that some of the xenoliths were amphibolites rather than anhydrous equivalents prior to their enclosure in the basic magma.
Delafossite and the system Cu–Fe–O
Authors: Buist D. S. , Gadalla A. M. M. , White J. 
Published: December 2006

SummaryAn investigation of the system Cu-Fe-O has established the existence of a phase near 3Cu2O.Fe3O4 and the non-existence of Cu2O.Fe2O3 a in the system over the range of oxygen pressures investigated.The X-ray diffraction patterns obtained from four samples of natural delafossite have been found to be similar to that obtained from a synthetic sample of the 3Cu2O.Fe3O4 phase. It has also been shown that, when heated under equilibrium conditions in the thermobalance in air, a sample of natural delafossite and the synthetic 3Cu2O.Fe3O4 behaved similarly.
Subsolidus solubility between : a hydrothermal investigation
Authors: Bradley R. S. , Engel P. , Munro D. C. 
Published: December 2006

SummaryThe subsolidus phase equilibrium of the lithiophilite-tephroite system was studied in the temperature range 500 to 900° C. The solubility of tephroite in lithiophilite is limited and increases with temperature. The reaction is very sluggish and has peculiar kinetic properties. No reverse solubility was observed. Similar asymmetry was found in the LiMgPO4-forsterite system of which a preliminary study was made. Apparent absences of silicate phosphate olivine solid solutions in nature are related to our experimental findings and to geological factors.
A test of the linearity of a photomultiplier used for reflectivity measurement
Authors: Phillips R. , Bradshaw P. M. D. 
Published: December 2006

SummaryA test of the linearity of a photomultiplier has been made using crossed polars as an optical attenuator. An expression is derived that allows for the measurable transmission of a polarizing filter in directions other than the permitted vibration direction. The linearity is shown to be adequate for accurate reflectivity measurement.
Distribution of magnesium and iron between metamorphic pyroxenes from Saltora, West Bengal, India
Authors: Sen S. K. , Rege S. M. 
Published: December 2006

SummaryFour orthopyroxene: calcic-pyroxene pairs from pyroxene-hornblende- and pyroxene-granulites from the Precambrians around Saltora, eastern India, have been chemically analysed. The distribution coefficients with respect to Mg-Fe (KD) are found to be 0·56, 0·57, 0·60, and 0·61, a set of values well within the limits characteristic of metamorphic parentage.
Rare earths in the aeschynite–priorite series. The status of lyndochite
Authors: Fleischer Michael 
Published: December 2006

SummaryData on the contents of individual rare earths are summarized for 24 members of the aeschynite-priorite series and 3 lyndochites. It is shown that the data are in accord with the assignment of lyndochite to the aeschynite-priorite series. The available X-ray data are not definitive, but indicate at least strong similarity of lyndochite to aeschynite ; the classification of lyndochite as a variety of euxenite is excluded.
A comparative electron-diffraction study of sillimanite and some natural and artificial mullites
Authors: Smith D. G. W. , McConnell J. D. C. 
Published: December 2006

SummaryElectron-diffraction photographs of some natural and synthetic mullites and a typical sillimanite have been obtained and are interpreted using diffraction data due to Agrell and Smith. The position and diffuseness of mullite reflections (h0l) with l = ½ have been re-studied. In such reciprocal lattice sections maxima are symmetrically disposed in pairs about the positions of sillimanite reflections with l odd. They lie on a* rows and show different separations in the specimens studied. These diffraction conditions are closely analogous to those observed in the intermediate plagioclases (paired ‘e’ maxima) and in nepheline, and a similar explanation is envisaged in terms of antiphase domain structure. Intimate association of a mullite-type phase and sillimanite is shown to result from the breakdown of muscovite in a thermal metamorphic aureole, and a chemical analysis of a natural Fe,Ti-bearing mullite from a spinel-mullite buchite in the same aureole, is presented.