bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotopic ages of the basic charnockite and khondalite from Kondapalli, Andhra Pradesh, India
Authors: Grasty R. L. , Leelanandam C.
Published: December 2006

The 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

Details 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

A 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.
The transformation of ankerite during thermal treatment
Authors: Dasgupta D. R.
Published: December 2006

The transformation of ankerite during heat treatment has been studied by single-crystal and powder X-ray methods. The mechanisms of formation of calcite at 750° C and of periclase at 950° C are discussed from a structural viewpoint.
Crystallography of psilomelane, A3X6Mn8O16
Authors: Mukherjee Bibhuti
Published: December 2006

Psilomelane 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

Zonal 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

The 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

In 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

An 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

The 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

A 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

Four 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

Data 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

Electron-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.
The occurrence of platinoid bismuthotellurides in the Merensky Reef at Rustenburg platinum mine in the western Bushveld
Authors: Kingston G. A.
Published: December 2006

Four different palladium and platinum bismuthotellurides, one containing major mercury, have been identified in the ore from Rustenburg mine on the Merensky Reef. The composition of each phase was determined by electronprobe microanalysis, and X-ray powder data are presented for three of these phases. Quantitative spectral reflectivity values at 470, 546, 589, and 650 mμ were obtained on areas of 1–10µ. Similar phases have been located in the ore from Union mine.

Two of these phases are shown to be moncheïte and kotulskite. From two electronprobe microanalyses, kotulskite is shown to be Pd(Te,Bi). The other two phases are new minerals: analysis of one of them gives the composition (Pd,Pt)(Te, Bi)2, containing 23·1% Pd, 1·8% Pt, 50·8 % Te, 14·2 % Bi, with strongest X-ray powder lines at 2·92 (10), 2·10 (6), 2·02 (3), and 1·54Å (3), and cell parameters a 3·978±0·001, c 5·125±0·002; it is probably isostructural with moncheïte, and an isomorphous series may exist between them; the name merenskyite is proposed for this mineral, after Dr. Hans Merensky who was mainly responsible for discovering the platinoid bearing ‘reef’; it is commonly intergrown with kotulskite. For the second new phase (Mineral A), no X-ray data could be obtained, but a single electron-probe microanalysis gave a composition of Pd 27·8 %, Hg 12 %, Te 38·5 % and Bi 1·6 % suggesting the empirical formula (Pd,Hg)(Te,Bi).
A new Czechoslovak occurrence of stokesite
Authors: Černý P.
Published: December 2006

The third occurrence of stokesite was discovered in a desilicated pegmatite at Věžná, Western Moravia. In this locality, stokesite accompanies columbite, cassiterite, and stibian pyrochlore-microlite, in a miarolitic cavity of albite. The X-ray data and the optical properties of the Věžná stokesite agree well with those observed by previous authors.
The alkali feldspars from microsyenitic dylces of southern Greenland
Authors: Scharbert H. G.
Published: December 2006

26 b-axis oscillation photographs of alkali feldspars of microsyenitic dykes of Southern Greenland are presented. The crystals are rather restricted in composition (Or42·4 to Or35·3) but are rather rich in Ca (up to 14 % An). The range of variation of the optic axial angles, 2 V 45° to 71° (exceptions up to 87°), puts the crystals between sanidine-anorthoclase cryptoperthite and orthoclase microperthite, as classified by Tuttle (1952).

Since the syenitic magma cooled down rather rapidly some peculiarities in the structural state of the alkali feldspars are to be expected. The potassium-rich phase is (nearly) monoclinic. According to the values of the reciprocal lattice angles α* and γ* the sodium-rich phases can be divided into three groups: high-temperature pericline-twinned and high-temperature albite-twinned phases, high-temperature pericline-twinned and low-temperature albite-twinned phases, and high-temperature pericline-twinned and low-temperature albite-twinned phases with nearly identical values of the reciprocal lattice angle γ*.
Graphite in natural and experimental carbonate systems
Authors: Gellatly D. C.
Published: December 2006

Graphite occurs in the Darkainle nepheline syenite complex, Somali Republic, as small drop-like grains in an altered ankeritic carbonatite; it has been recorded previously from carbonate-bearing nepheline syenites and kimberlites. Experimental evidence indicates that siderite decomposes to a stable association of magnetite and graphite within the PT ranges 500 to 10 000 bars and 455 to 745° C. The graphite in carbonatite and other alkaline igneous rocks may have been formed similarly by the decomposition of siderite or iron-rich carbonates.
The feldspars of the Rosses Granite Complex, Donegal, Ireland
Authors: Hall A.
Published: December 2006

An examination has been made of the composition and structural state of the feldspars in each of the units of the Rosses granite complex. The compositions of the plagioclases are systematically related to the compositions of the rocks, but the alkali feldspars are much more uniform as a result of postmagmatic recrystallization. In the granites both alkali feldspar and plagioclase are in low-temperature structural states, but alkali feldspar phenocrysts from one of the porphyry dykes associated with the complex show a higher-temperature state.
The analysis of molybdates and tungstates
Authors: Easton A. J. , Moss A. A.
Published: December 2006

The estimation of molybdenum and tungsten when present together has proved difficult, as is indicated by the large number of methods put forward for their determination. Many of the methods given are for one or other of these elements only, a note often being added that the presence of the other invalidates the method. The estimation of molybdate and tungstate in the mineral powellite has been briefly described by one of the authors (A. A. M.): molybdate and tungstate were precipitated as oxinates (Mo,W)O2(C9H6ON)2 and the molybdate (MoO4″) determined by measurement of the optical density at 230 mµ of a solution containing molybdate and tungstate. The amount of tungstate present was then estimated by difference. The property of the molybdate ion, MoO4″, to absorb strongly in the ultra-violet has been further investigated and it has been found that, if a wave-length of 240 mµ is chosen and the proper precautions taken, the MoO4″ ion can be estimated without significant interference by the WO4″ ion. Methods are given for the analysis of the common molybdate and tungstate minerals, together with results obtained during the course of this investigation.
Clinopyroxenes from the Square Top intrusion, Nundle, New South Wales
Authors: Wilkinson J. F. G.
Published: December 2006

Despite a wide range in parent rock compositions, from analcime-olivine theralite to analcime-tinguaite, clinopyroxene phenocrysts in the Square Top intrusion show limited compositional variation. The crystallization trend of the pyroxenes (principally sahlites) lies approximately parallel to the diopside-hedenbergite join of the pyroxene quadrilateral, and in addition reveals slight enrichment in acmite. The limited iron enrichment in the pyroxenes (and in olivine phenocrysts in the theralites and tinguaites) stemmed from progressively more hydrous liquid fractions whose ferric/ferrous iron ratios increased during differentiation.
The weathering of biotite in some Aberdeenshire soils
Authors: Wilson M. J.
Published: December 2006

The weathering of biotite in some freely drained soils developed from a biotite-rich quartz gabbro near Strathdon, Aberdeenshire, has been studied. Using a combination of X-ray, chemical, differential thermal, infra-red, and optical techniques, it was found that the biotite weathers to an intergrade aluminous vermiculite-chlorite together with zones of kaolinite and gibbsite. The crystallographic axes of biotite and included kaolinite are common and parallel and it is proposed that both kaolinite and gibbsite zones crystallized epitaxially within opened out cleavage spaces of the host biotite. The development of kaolinite and gibbsite in this manner could have occurred relatively quickly and the significance of this with regard to generalized pedogenic weathering reactions of biotite is discussed.
Experimental studies of apatite crystallization in parts of the system CaO-P2O5-H2O at 1000 bars
Authors: Biggar G. M.
Published: December 2006

Solid-liquid-vapour phase equilibria for the join Ca(OH)2-Ca3(PO4)2-H2O at 1000 bars are determined in the temperature range 700 to 950°C. The isobaric invariant equilibrium portlandite + hydroxyapatite → liquid on the join Ca(OH)2-Ca3(PO4)2 involves a liquid with the composition 96 wt. % Ca(OH)2, 4 wt. % Ca2(PO4)2 and occurs at 765°C. The isobaric invariant equilibrium portlandite + hydroxyapatite + vapour → liquid on the join Ca(OH)2-Ca3(PO4)2-H2O is encountered at 735°C, and involves a liquid containing 92 wt. % Ca(OH)2, 4 wt. % Ca3(PO4)2, and 4 wt. % H2O. The apatites are shown by X-ray diffraction techniques to vary in composition with changes in the bulk composition from which crystallization occurred.

The apatite liquidus is steep; apatite is the first mineral to crystallize from calcium-hydroxide-rich liquids containing as little as 4 wt. % Ca2(PO4)2 (1·8 % P2O5) at temperatures as low as 735°C in the presence of vapour at 1000 bars pressure; and rapid crystal settling of apatite was experimentally noted. These observations suggest that concentrations of apatite in carbonatites are the result of crystal accumulation from liquids relatively poor in P2O5.
Paragenesis of the metasomatic actinolite-bearing rocks from the Khetri copper belt, Rajasthan, India
Authors: Das Gupta S. P.
Published: December 2006

In the south-eastern part of the Khetri copper belt, actinolite occurs in association with alteration assemblages resulting from the Fe-Mg metasomatism that accompanied sulphide mineralization, and more commonly with albite-bearing rocks formed by albitization of quartzites and schists near granitic rocks. Within the latter occur many coarse, massive, and unoriented aggregates of actinolite crystals, individuals being commonly more than 10 cm long. Locally fluorite-bearing veins oecur within granitic and albite-quartz rocks. The actinolite is pleochroic from pale pink to green; γ: [001] = 26°; γ = 1·642 ± 0·003; 2Vα = 80°. The composition of the analysed actinolite closely compares with those published in the literature excepting in (OH), which is low. The mineral assemblages, formed by metasomatic replacement of pre-existing rocks, are equivalent to those of albite-epidote-amphibolite facies. The metasomatic fluid was apparently rich in Ca, F (indicated by fluorite), and oxygen (indicated by magnetite, ilmenite, and hematite).
The mineralogy of the potassium-barium feldspar series. II. Studies on hydrothermally synthesized members
Authors: Roy N. N.
Published: December 2006

Members of the KAlSi3O8-BaAl2Si2O8feldspar series have been synthesized by hydrothermal methods. Although the products are too finely crystalline for complete detailed study, some X-ray and optical measurements have been made, together with some electron-diffraction observations.

The results presented confirm the existence of high structural states over the greater part of the series, and suggest that a simple solid-solution series is formed between the end-members at high temperatures.
Phosphates and other minerals in pegmatites of Rhodesia and Uganda
Authors: Gallagher M. J.
Published: December 2006

In the rich mineral assemblage found in the pegmatites of Rhodesia and Uganda are members of the amblygonite-montebrasite series with α 1·592–1·615, γ, 1·612–1·638, the highest values corresponding to montebrasite, Li1·98Al2·00 (P1·95O7·90)(OH1·90F0·20); apatite with up to 8·8 per cent MnO; heterosite (new analysis) and other manganese-iron phosphates; and a variety of niobium-tantalum and uranium minerals.
Genthelvite and bertrandite from the Cairngorm Mountains, Scotland
Authors: Morgan W. C.
Published: December 2006

A zinc-rich helvine (genthelvite) has been found with bertrandite in miarolitic cavities in adamellite at Coire an Lochain in the Cairngorm Mountains. The genthelvite occurs as green or brown tetrahedral crystals of sp. gr 3·58±0·01. It is isotropic, n 1·742±0·003, a 8·133±0·005 Å. Bertrandite crystals are pale brown with sp. gr. 2·60±0·01; biaxial negative with 2V 75°, and α 1·590, β 1·603, γ 1·613, all ±0·003.
Garnets as indices of progressive regional metamorphism
Authors: Nandi Kamal
Published: December 2006

Garnets undergo readjustment of ion-assemblages under external mechanical and thermal stresses; this adjustment favours those paths that annul the very cause to which it is due. Metal ions in garnets being replaceable, with rising metamorphism garnets become reluctant to accommodate ions of larger ionic radii.

Data from recent literature on chemical analyses of garnets from rocks belonging to different grades of regional metamorphism reveal that the (FeO + MgO) content of garnet varies linearly with (CaO + MnO) content. As the Fe/Mg ratio does not vary appreciably, a fair estimate of metamorphic grade can be made from a knowledge of (CaO + MnO) or of (FeO +MgO) individually or even, with less confidence, of FeO or MgO alone. From the study of the available data it is found that (CaO + MnO) and (FeO + MgO)/(CaO + MnO) provide the best indicators of progressive metamorphism. Cell edges of garnets decrease progressively with increasing metamorphism and this may also be used as a fairly good index of metamorphism. When cell edges are plotted against (FeO + MgO)/(CaO + MnO), a hyperbolic curve is obtained.
Measurement of the modal composition of a granitic rock powder by point-counting, infra-red spectroscopy, and X-ray diffraction
Authors: Bradshaw P. M. D.
Published: December 2006

A rapid method for determining the mode of a four-component powder (microcline, orthoclase, plagioclase, and quartz) was sought to aid the interpretation of geochemical results. An accuracy of about ±5 % (absolute) was required. Three methods were tried : point counting proved too long as well as destroying the sample; infra-red spectroscopy was not sufficiently accurate for this particular type of rock powder; X-ray diffraction proved the most rapid and, although less accurate than point counting, was within acceptable limits and had the advantage of giving additional information about the composition of the feldspars.
Methods for the chemical analysis of meteorites: II. The major and some minor constituents of chondrites
Authors: Moss A. A. , Hey M. H. , Elliott C. J. , Easton A. J.
Published: December 2006

Pure dry chlorine at 250 to 350° C is shown to have no action on the principal silicate and phosphate phases of meteorites, but reacts quantitatively with the sulphide and phosphide phases and with kamacite; taenite does not react if it contains more than about 20 to 25 % Ni; some rare meteoritic minerals have not yet been tested. Volatile chlorides (including SiCl4) distil, and non-volatile chlorides can be leached out with water. Based on these observations, a method has been devised and applied to the analysis of a number of chondrites and to the purification of olivine and pyroxene separated by physical methods. The amount of Si present in the metal of enstatite chondrites, and the distribution of P, Ga, Ge, Ti, Cr, Mn, Ca, and Mg between oxidized and non-oxidized phases can readily be determined, and some results are presented. From the limited data so far available, Co appears to be concentrated in kamacite; gallium in the metallic phase is mainly in the taenite; germanium is strongly siderophile in the common chondrites but some is present in the silicate of the enstatite chondrites; titanium is markedly chalcophile in the enstatite chondrites, less so in the common chondrites, and the same applies to chromium; phosphorus is present as phosphide in the enstatite chondrites, but as phosphate in the hypersthene chondrites.
The Woodbine meteorite, with notes on silicates in iron meteorites
Authors: Mason Brian
Published: December 2006

The Woodbine meteorite, ploughed up in Illinois in 1953, is a fine octahedrite with numerous inclusions of silicate minerals. The minerals present include kamacite, taenite, troilite, schreibersite, orthopyroxene (Fs6), diopside, olivine (Fa4), plagioclase (An9), and graphite. The chemical analysis is: Fe 73·06, Ni 9·08, Co 0·15, P 0·47, C 0·21, FeS 1·65, SiO2 8·55, TiO2 0·02, Al2O3 0·53, Cr2O3 0·03, FeO 0·49, MnO 0·03, MgO 5·19, CaO 0·34, Na2O 0·29, K2O 0·02, sum 100·11. Woodbine is compared with other meteorites of similar composition. The silicate material has chondritic composition, and is quite different from the silicate material of the mesosiderites, with which some of these meteorites have been classed.
Chemical study of pyroxenes from the charnockitic rocks of Kondapalli (Andhra Pradesh), India, with emphasis, on the distribution of elements in coexisting pyroxenes
Authors: Leelanandam C.
Published: December 2006

The chemical analyses, structural formulae, and trace element data are presented for 18 orthopyroxenes and 9 clinopyroxenes from the charnockitie rocks of Kondapalli, Andhra Pradesh, India. The chemistry of these pyroxenes is discussed and conclusions are drawn. The data are compared with the similar data available for the pyroxenes of the charnockites of the type area near Madras, some 200 miles south of Kondapalli. The element-distributional relationships between the coexisting pyroxenes are discussed and inferences are made regarding the temperature of crystallization of charnockite pyroxenes.
Vlasovite: a second occurrence and a triclinic to monoclinic inversion
Authors: Fleet S. G. , Cann J. R.
Published: December 2006

Vlasovite, Na2ZrSi4O11, previously reported as monoclinic by Pyatenko and Voronkov from an occurrence in the Kola Peninsula, Russia, has been found in rocks from Ascension Island in a triclinic twinned modification. The obliquity is very slight (α and γ, differ from 90° by less than 1°), and X-ray photographs show arrays of paired spots corresponding to diffraction by different parts of the crystal related by the twinning operation, reflexion across (010).

On heating, this vlasovite is found to transform to the monoclinic variety at 29° C. The phase change has been followed on a single-crystal X-ray heating camera, and the obliquity is found to have successively smaller values as the crystal is heated from temperatures below room temperature to 29° C. The obliquity is characteristic of the particular temperature over the transformation range and is not affected by thermal history.

The transformation appears to be a displacive one, similar in some respects to α → β tridymite and α → β cristobalite, and some information has been obtained by X-ray structural investigations about the nature of the atomic movements involved.
Some manganese oxide pseudomorphs
Authors: Davis R. J.
Published: December 2006

Pyrolusite pseudomorphous after manganite occurs at Serro do Navio, Amapa, Brazil. It consists of wedges, flattened on (100) and elongated along [010], twinned on (011) and showing forms d{210}, , b{010}, and f{021} (all indices referred to manganite, in the setting of Dana, 7th edn). The difficulty of distinguishing between pyrolusite pseudomorphous after manganite and after groutite is discussed and also the possible existence of the latter. The distinction was made here by measuring the twinning angle between the pyrolusite lattices using (0kl) precession photographs. Specimens of manganite intergrown with pyrolusite are described and their relative orientations determined. On heating, manganite partly decomposes to a monoclinic phase, a 9·9 Å, b 5·73 Å, c 4·89 Å, β 98°, space group I2, Im, or I2/m.
X-ray data on some calcium-iron-oxygen compounds
Authors: Hughes H. , Roos P. , Goldring D. C.
Published: December 2006

Synthetic mixtures of CaO and Fe2O3 fired in air at temperatures in the range 1180° C to 1240° C in some cases lost oxygen and formed ferrous-iron-bearing compounds. Samples after firing were examined by incident light microscopy and X-ray diffraction; new powder data are presented for the phases reported. In addition to α-Fe2O3, CaFe2O4, and Ca2Fe2O53. four distinct phases have been identified. These are and two forms of , described previously by Braun and Kwestroo (1960). The likely compositions of these phases are given.
The olivine, pyroxene, and metal content of chondritic meteorites as a consequence of Prior's rule
Authors: Mueller Robert F. , Olsen Edward J.
Published: December 2006

There is an important corollary to Prior's rule to the effect that as the state of oxidation of meteorites is increased the quantity of olivine increases relative to pyroxene and metallic iron. We have derived a rigorous parametric expression for this corollary and find that, as in the case of the quantitative interpretation of the rule itself, there is in this case also a fair correspondence to the observational data, so that the validity of the rule is further supported.
An exceptionally large chondrule in the Parnallee meteorite
Authors: Binns R. A.
Published: December 2006

A giant chondrule, nearly 4 cm in diameter, has been found in the Parnallee meteorite, and is described, with analysis. An estimate of the composition of the partly devitrified groundmass falls within the known compositional range of chondrule glasses. The bulk composition of the chondrule is very close to the bulk composition of the meteorite excluding metal and sulphide.
The hydroxyl-stretching region of the biotite mica spectrum
Authors: Wilkins R. W. T.
Published: December 2006

An interpretation of part of the hydroxyl-stretching region of the infra-red absorption spectrum of biotite is proposed. A consideration of band shapes enables the interpretation to be quantified and tested against a series of natural biotites. The equation derived may be used to determine the atomic ratio Mg2+/(Mg2++Fe2+) in biotites but the necessary assumptions and simplifications make it unlikely that the method will be very useful in practice.
The petrochemistry of some Lewisian granitic rocks
Authors: Bowes D. R.
Published: December 2006

The chemical compositions of eighty granitic rocks from the Lewisian of the North-West Highlands of Scotland, particularly from the Gairloch district, are set out in relation to geological occurrence and their normative proportions of albite, orthoclase, quartz, and anorthite compared with experimental data relating to the systems NaAlSi3O8-KAlSi3O8-SiO2-H2O and KAlSi3O8-NaAlSi2O8-CaAl2Si2O8-SiO2. The field of composition for these Lewisian rocks moves from Ab-Q-rich for autochthonous granites to Ab = Or = Q (approximately) for parautochthonous granites to Or-rich for intrusive granites. This trend is related to the varying roles of mineral solubility under stress, selective melting, and potassium metasomatism.
Trace elements in pyroxenes and amphiboles from ultramafic rocks of the Urals
Authors: Borisenko L. F. , Борисенко Λ. Φ.
Published: December 2006

The minor elements Li, Sc, V, Cr, Co, Ni, Ga, Rb, and Sr have been determined in a number of diopsides and horneblendes from ultramafic rocks of the Gussevogorsk, Baranchinsk, and Nizhne-Tagilsk massifs in the Urals. Actinolite and anthophyllite are rare contact metamorphic products ; they too were analysed. The diopside and hornblende from the earlier-formed rocks, richer in olivine, contain more Cr and less V and Ti than those from the later-formed rocks.
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

Earlier 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

The 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

The 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

Myrmekite-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

Some 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

Some 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

Phase 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

For 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

A 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

The 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

The 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

Calcium 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

These 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

The 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

An 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

Thermal 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

Calzirtite, 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

A 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.