bluuebunny/crossref_metadata_2025 huggingface dataset:
The aqueous chemistry of uranium minerals. Part I. Divalent cation zippeïte
Authors: Haacke David F. , Williams Peter A.
Published: December 2006

Synopsis

Free energies of formation of divalent metal ion zippeïtes, M2(UO2)6(SO4)3(OH)10 ·nH2O, M = Mg,Co,Ni,Zn have been determined from solution studies and metal speciation calculations, in water. It is found that in the compounds, the number of molecules of water of crystallization is equal to 8. This is at variance with a previous report (Frondel et al., 1976), but it has been found that some at least of the water content of zippeite is either nonessential or very loosely bound in the structure. Based on the octahydrate formulation, values are −3506, −12695, −12683 and −12870±4 kJ mol−1 for the Mg,Co,Ni and Zn end-members, respectively. Almost all of the differences in the values are accounted for by those values for the metal ions alone with the exception of Znzippeïte where a discrepancy of some 22 kJ mol−1 is found. Even this value is small however, and the chemical studies indicate that extensive mutual solid solution between all end members is to be expected. These findings agree perfectly with observations on the composition of naturally occurring zippeite minerals of this group.
The occurrence of högbomite and taaffeite in a spinel-phlogopite schist from the Mount Painter Province of South Australia
Authors: Teale Graham S.
Published: December 2006

A spinel-phlogopite schist from the Mount Painter Province of South Australia forms part of a highly magnesium- and aluminium-rich unit and contains the minerals högbomite and taaffeite. Taaffeite nucleated in spinel during upper amphibolite facies metamorphism. During a subsequent upper amphibolite facies metamorphic event both spinel and taaffeite were partially replaced by högbomite. Chemical analyses of högbomite, taaffeite, and spinel are presented.
The occurrence of cebollite in kimberlite and included zeolitized crustal xenoliths
Authors: Kruger F. J.
Published: December 2006

Two different parageneses for cebollite, a rare hydrated calcium aluminium silicate, are described, both differing from all previously reported occurrences.

Cebollite forms concomitantly with natrolite from plagioclase in xenoliths of crustal material incorporated in kimberlite. The mineral also occurs as a late stage primary mineral in a phlogopite-rich kimberlite.

Tentative models for the genesis of the mineral in the environments described are proposed. It is suggested that the final stages in the crystallization of diatreme-facies kimberlite are dominated by fluids rich in lime and having a low partial pressure of CO2.
Petrogenesis of alnöitic rocks from Malaita, Solomon Islands, Melanesia
Authors: Nixon Peter H. , Mitchell Roger H. , Rogers Nicholas W.
Published: December 2006

Aphanitic and fragmental alnöitic rocks from Malaita contain ultrabasic xenoliths and discrete nodules (megacrysts) of pyroxenes and garnets. Primary minerals in the alnöites are olivine (Fo85), clinopyroxene (diopside-sahlite), natro-melilite (1/3 melilite-2/3 åkermanite), phlogopite (1–9% TiO2), perovskite, spinel (ulvö spinel-magnetite series) and accessory nepheline, melanite, and apatite. Alnöite olivines and clinopyroxenes are compositionally different from those phases in the xenoliths and megacrysts. Rare earth element distribution patterns are linear and indicate strong enrichment in the light rare earths (La/Yb = 42−49). The alnöites are possible primary melts of a pyrolite-type mantle formed by approximately 4% partial melting at depths greater than 120 km, under high carbon dioxide pressures. Despite containing a mantle xenolith assemblage similar to that found in kimberlites, the host Malaita rocks are minera-logically and geochemically different from kimberlite.
Apachite and gilalite, two new copper silicates from Christmas, Arizona
Authors: Cesbron F. P. , Williams S. A.
Published: December 2006

Both new species are retrograde or mesogene minerals that occur in tactites at the Christmas mine, Gila County, Arizona (USA). Gilalite is green, H = 2, D = 2.82. Biaxial (—), 2V small, α = 1.560, β = γ = 1.635. No single crystals found; strongest lines at 13.49 Å, (10); 10.97 (5); 7.786 (5). Analysis gave CuO 36.2%, MgO 2.3, CaO 3.8, MnO 0.5, SiO2 41.5, H2O 14.6, close to Cu5Si6O17·7H2O.

Apachite is blue, H = 2, D = 2.80. Biaxial (—), 2V small, α = 1.610, β = γ = 1.650. No single crystals found. Strongest lines are 12.90 Å (10); 3.168 (7); 7.663 (5). Analysis gave CuO 43.6%, FeO 0.3, MgO 1.7, CaO 1.8, SiO2 40.8, H2O 13.8, close to Cu9Si10O29·11H2O.
The aqueous chemistry of uranium minerals. Part 2. Minerals of the liebigite group
Authors: Alwan Alwan K. , Williams Peter A.
Published: December 2006

Synopsis

Free energies of formation of liebigite, Ca2UO2 (Co3)3·10H2O, swartzite, CaMgUO2(Co3)3·12H2O, bayleyite, Mg2UO2(CO3)3·18H2O, and andersonite, Na2CaUO2(CO3)3·6H2O have been determined from solution studies at various temperatures. ΔGf(298.2K)° values for the above minerals are −6226±12, −6607±8, −7924±8 and −5651±24 KJ mol−1 respectively. ΔH0f(298.2K) values respectively are −7037±24, −7535±20, −9192±20, and −5916±36 kJ mol−1. These results have been used to construct the stability diagram for the four minerals shown in fig. I. Andersonite can only form when the activity of the sodium ion, aNa+, is relatively high and aCa2+ and aMg2+ are small. The interconversions of the sodium-free species are defined. When aMg2+/aCa2+ < 0.32 liebigite is the stable phase. If aMg2+/aCa2+ > 7.94, bayleyite forms preferentially. One might therefore expect the bayleyite-andersonite association to be more common than liebigite-andersonite, but this is entirely dependent upon the relative concentrations of Mg2+(aq) and Ca2+(aq) in the solutions from which the minerals form.
The uranium content of garnet lherzolite xenoliths from kimberlites
Authors: Carswell D. A. , Rice C. M.
Published: December 2006

Uranium contents ranging from 0.03–1.18 ppm have been determined by delayed neutron activation analysis in a suite of 19 ultrabasic xenoliths (mostly of the common garnet lherzolite type) from the kimberlites of southern Africa. Consideration of these and previous data lead us to conclude that the U content of uncontaminated garnet lherzolite in the uppermost mantle is on average roughly 0.04–0.05 ppm, levels which are sufficient to account for the observed U contents of fresh basalts. Higher U contents in mantle-derived ultrabasic xenoliths are the result of secondary alteration processes, most probably related to infiltration metasomatism stemming from contact with kimberlitic or carbonatitic magma fractions. This introduced U is concentrated along the boundaries of the primary mineral grains and is mostly readily removed by acid leaching. A partial analysis is given for a secondary uraniferous calcium phosphate phase observed in kelyphitic rims around garnets.
Anatexis and high-grade metamorphism in the Champira Dome, Malawi: petrological and Rb-Sr studies
Authors: Haslam H. W. , Brewer M. S. , Davis A. E. , Darbyshire D. P. F.
Published: December 2006

Banded gneisses and migmatites in the Champira Dome contain assemblages of the biotite-cordierite-almandine subfacies of the granulite facies. The banded gneisses represent a sequence of arkosic sediments metamorphosed to sillimanite-cordierite gneisses. The migmatites were derived from more argillaceous and potassic sediments, with lower oxidation ratios and lower Ba/Rb ratios. They consist of a quartzo-feldspathic leucosome, representing anatectic melt, with schlieren of the refractory minerals sillimanite, garnet, biotite, and oxide minerals. Cordierite developed from garnet and biotite, except in rocks of high FeO/(FeO + MgO) ratio. Both rock types contain assemblages of magnetite + hercynite + corundum + ilmenite + hematite, formed by unmixing of high-temperature solid solutions. Rb-Sr studies of the banded gneisses gave an age of 2327 ± 25 Ma, which is interpreted as the date of metamorphism, and an initial 87Sr/86Sr ratio of 0.7064 ± 0.0003. The migmatite samples plot close to this 2327 Ma regression line, but the strontium isotopes were considerably disturbed, though not homogenized on the scale of sampling, 962 ± 34 Ma ago. It is considered that the anatexis in the migmatites was contemporaneous with the metamorphism of the banded gneisses and that the 962 ± 34 Ma event may be correlated with recrystallization of the migmatites accompanying the growth of cordierite.
Ortho- and clinopyroxenes from the pyroxene granulites of Swat Kohistan, northern Pakistan
Authors: Qasim Jan M. , Howie R. A.
Published: December 2006

This paper presents wet chemical analyses of forty-one pyroxenes (thirty-nine of them new) from pyroxene granulites and a few neighbouring rocks from Swat Kohistan and the adjoining Indus Valley. The granulites, considered to be derived from plutonic norites of an island arc tholeiitic nature, constitute one of the most extensive belts of its kind in the world. The pyroxenes are not unusual in any respect but they bear a closer resemblance to metamorphic than to igneous pyroxenes crystallized from deep-seated tholeiitic magmas. The distribution of Mg, Fe, and Mn (average KDMg−Fe=0.57) and the tie-line intersections on the Wo-En join (generally from Wo80.5to Wo76.5) between the coexisting eighteen pyroxene pairs from the granulites are discussed. Based on eight different methods of geothermometry and other considerations, it is concluded that the pyroxene granulites were metamorphosed at around 800°C and 7 to 8 kbar.
Ferroan carrollites, cobaltian violarites, and other members of the linnaeite group: (Co,Ni, Fe,Cu)3S4
Authors: Riley John F.
Published: December 2006

Electron microprobe analyses and X-ray data are given for iron-rich carrollites, cobaltian violarites, and other members of the linnaeite group. The iron-rich carrollites (8.5 wt% Fe) occur as an unmixed phase in a copper linnaeite host from the Zambian Copperbelt. Primary and secondary cobaltian violarites are reported from Rhodesia and Australia respectively with the latter recording up to 19.2 wt% Co. A diagrammatic review is given of the extremes of composition reported within the group together with the more reliable cell sizes.
Analcime from the L. Lias on the W. Somerset coast
Authors: Alabaster C. J.
Published: December 2006

Analcime, occurring both as small, pale-brown trapezohedral crystals and pale-brown slaggy masses, is reported growing into and replacing aragonitic shell debris in a heavily faulted, 15-km long, coastal exposure of L. Jurassic marine sediments. Associated minerals include authigenic baryte, sphalerite, pyrite (some framboidal), celestine, aragonite, calcite, dolomite, quartz, and solid hydrocarbon. No other zeolites have been found. Its modes of occurrence, crystal morphology, and relationships to these minerals are described. The analcime appears to be restricted in occurrence to the W. Somerset coast. Partial chemical analysis of one sample is given. The brown colouration is suggested to be due to organic compounds. XRD analysis of five samples reveals progressive decrease in silica content towards western extremity of the exposure. No evidence of volcanic ash contamination of the sediments is found. A hydrothermal origin is discounted; formation of the analcime by purely diagenetic processes is suggested.
The nickel telluride mineral melonite from the Jaduguda uranium deposit, Singhbhum Shear Zone, Bihar, India
Authors: Krishna Rao N. , Narasimhan D. , Rao G. V. U.
Published: December 2006

The rare nickel telluride mineral melonite is identified from Jaduguda uranium ore, Singhbhum Shear Zone, Bihar, India. Its physical, optical, chemical, and paragenetic characteristics are described. The composition as obtained by EPMA is NiTe1.66Bi0.06 or approximately Ni3(Te,Bi)5. The association of melonite with molybenite in this ore deposit is unusual, since melonite is generally associated with tellurides of gold and silver. This is the first reported occurrence of melonite from India.
Assimilation and metamorphism at a basalt-limestone contact, Tokatoka, New Zealand
Authors: Baker C. K. , Black Philippa M.
Published: December 2006

Small-scale assimilation of limestone during the intrusion of an olivine basalt feeder dyke into an Eocene argillaceous, siliceous biomicrite in the Tokatoka area has resulted in the incorporation of large amounts of calcium into the parent magma. Initial effects of assimilation have caused partial resorption of the early-formed igneous mineralogy and the precipitation of calcic, iron-rich clinopyroxenes (ferrosahlite to hedenbergite), wollastonite, schorlomite, and pyrrhotine. Pyroxene compositions show a trend of strong enrichment in Catschermak and ferrosilite components. Derivative hydrothermal solutions, rich in Ca, Si, Al and alkalis have precipitated and altered anhydrous phases to tobermorite, thomsonite, prehnite, pectolite, cebollite, hydrogrossular, gismondine, analcime, Sr- and Ba-bearing zeolites, and calcite.

Modelling of the basalt-limestone assimilation process by least-squares mixing methods has shown that the observed chemical variation can largely be accounted for by the dilution of the basalt with up to 30 wt. % decarbonated limestone. Desilication of the liquid, a result of this dilution effect, has been accommodated in the chemistry of the early-formed mineralogy rather than by the crystallization of minerals characteristic of an undersaturated rock type.

Contemporaneous with the intrusion of the basalt was the high-temperature contact metamorphism of the limestone. This produced assemblages of rankinite, kilchoanite, larnite, spurrite, grossular, and tobermorite. Subsequent injection of the basalt and hybrid phases into fractures has resulted in the alteration of the primary metamorphic assemblage to wollastonite, scawtite, foshagite, hydrogrossular, calcite, and vaterite.
Morphology, twinning, and optical orientation of gismondine
Authors: Nawaz Rab
Published: December 2006

Gismondine is a monoclinic mineral but prior to X-ray determination of its unit cell it was variously regarded as orthorhombic, monoclinic, or triclinic on account of its intricate twinning. A study of gismondine crystals from Osa Quarry, near Rome, indicates that the morphologically dominant form is {32} which by twinning about the normal to {100} produces penetration-twinned octahedral crystals united on (100) and (001). Gismondine has poor cleavage on {32} optic plane is (010) and γ:[001] = 42.5° (in obtuseβ).
Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales
Authors: Robinson D. , Nicholls R. A. , Thomas L. J.
Published: December 2006

Illite crystallinity determinations on Palaeozoic pelitic rocks, whose stratigraphic range runs from Lower Cambrian to Westphalian, indicate that anchimetamorphism has affected both the Lower and Upper Palaeozoic sequences. Two metamorphic episodes are in evidence, with the earlier, Caledonian, being of slightly higher grade. The higher anchizone crystallinity values are recorded from the Fishguard area in which mineral assemblages of the prehnite-pumpellyite facies have recently been recognized in basic igneous rocks. The later metamorphic episode has affected rocks to the south of the Variscan front. Here crystallinity values are low anchizone but some straddle the boundary with the diagenetic state. The Pembroke coalfield lies in this southern area and has coals largely of anthracite rank with volatile matter contents of between 10.1 and 5% Grade of metamorphism as indicated by crystallinity and by coal rank data from the Pembroke coalfield shows anomalous results to that described from the main South Wales coalfield. A neo-formed 2M illite from the Variscan spaced cleavage is described with analytical and X-ray diffraction data.
Bismutohauchecornite—new name: hauchecornite redefined
Authors: Just J.
Published: December 2006

The name hauchecornite has been applied in the literature to a group of minerals with similar crystal structures and the general formula (Ni,Co,Fe)9ABS8, where A and B are As, Sb, Bi, and Te in two nonequivalent structural sites. A classification of the group is proposed based on the relative abundance of the elements As, Sb, Bi, and Te in the two sites. Hauchecornite is redefined as Ni9BiSbS8, the end-member being closely approximated by the composition of the material from the type locality, and a new name, bismutohauchecornite, is proposed for the Ni9Bi2S8 end-member. The classification, redefinition, and the new name have been approved by the Commission on New Minerals and Mineral Names, IMA.
A re-examination of cheralite
Authors: Bowles J. F. W. , Jobbins E. A. , Young B. R.
Published: December 2006

A new analysis of the type material of cheralite specifies the individual rare earth elements. Unit cell contents are: (REE1.58Th1.15Ca1.03Pb0.05U0.15)3.96 (P3.67Si0.33)4.01O16. Refinement of the cell parameters based on new XRD data shows that a = 6.7515 ± 0,0005 Å, b = 6.9625 ± 0.0005, c = 6.468 ± 0.0005, β = 103° 53′, giving a cell volume of 295.2 Å3. Space group P21/n.
The diffusion of Fe2+ ions in spinels with relevance to the process of maghemitization
Authors: Freer W. , O'Reilly R.
Published: December 2006

The maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.
Changes in crystal morphology of synthetic reedmergnerite (NaBSi3O8) during ordering experiments
Authors: Mason R. A.
Published: December 2006

The morphologies of hydrothermally grown reedmergnerite crystals change systematically with time and rate of change of B, Si order. Three stages in this process are recognized: (1) Growth of well-faceted crystals. (2) Development of etching leading to the formation of irregular grains. (3) Modification of irregular grains to form rounded or ellipsoidal crystals. A solutionreprecipitation process is responsible for the morphological changes and the increase in degree of order of B and Si with time at constant temperature and pressure.
An optical anomaly possibly due to optical activity in some uniaxial opaque ore minerals
Authors: Hall A. J. , Cervelle B. D. , Simpson P. R.
Published: December 2006

Spectral reflectance measurements on three uniaxial ore minerals, tellurium, chalcopyrite, and stibioluzonite, which are opaque at least in the visible part of the spectrum have revealed that the reflectance curve of the ordinary ray varies with crystallographic orientation of the polished section. The three minerals possess symmetries capable of exhibiting optical activity in transmitted light. A possible explanation, therefore, of the anomalous behaviour is that the optical constants, i.e. the refractive index and the absorption coefficient, and thus also the reflectance, of the ordinary ray may differ for sections cut normal to c where optical activity probably has its maximum effect and for sections cut parallel to c where there is probably little or no complication due to optical activity. There would therefore appear to be a need to extend the theory of reflection from absorbing media to include reflection from optically active absorbing minerals.
An evaluation of the performance of an inductively coupled plasma source spectrometer for the determination of the major and trace constituents of silicate rocks and minerals
Authors: Walsh J. N. , Howie R. A.
Published: December 2006

The results of a study on the suitability of the inductively coupled plasma source spectrometer for the analysis of rocks and minerals are presented. The preparation of a stable solution of the elements to be measured is a prerequisite, and methods of sample preparation are described. It is shown that it is possible to measure all the major elements (excluding H2O and Fe2+) with acceptable precision and accuracy, and a wide range of trace elements down to the ppm level in the rock or mineral. Excluding sample preparation time, analysis and print-out of results as percent or ppm requires 1–2 minutes for complete analysis. Data on possible interferences (spectral line overlap etc.) are presented and, using some analyses of rocks and minerals comparisons are made with other analytical methods.
Ferroglaucophane- and chloritoid-bearing metapelites from the phyllite series, southern Peloponnese, Greece
Authors: Katagas Christos
Published: December 2006

The unusual assemblage ferroglaucophane-chloritoid-paragonite-garnet-muscovite-chlorite-quartz has been found in metapelites of the phyllite series, north-east of Neapolis, southern Peloponnese, Greece. The chemical compositions of the coexisting phases are given, and the physical and chemical constraints which may control the appearance of this assemblage are briefly discussed.
The structural role of Fe 3+ in biotites from the Euganean Hills, Italy
Authors: De Pieri Renzo
Published: December 2006

Plots of partition coefficient (mineral/matrix) against ionic radius of the elements in seventeen biotites from trachytes and rhyolites of the Euganean Hills do not show differences in the type of diagram between the biotites with tetrahedral sites completely filled by Si and Al, and those in which filling is only possible with the intervention of Fe3+ (or Ti4+) since these sites are incompletely filled by Si and Al. This behaviour seems to exclude, for the latter, the presence of Fe3+ (or Ti4+ in the tetrahedral site. Similar indications are given by structural analysis. The possibility of existence of [(OH)4]4− groups or, more probably, vacancies in these sites is therefore suggested. The consequences that these results would have on the possibility of correct calculation of the crystallo-chemical formula are discussed.
Petrofabrics of laminated gabbros from the Centre 3 igneous complex, Ardnamurchan, Scotland
Authors: Fortey N. J.
Published: December 2006

Petrofabric analysis of five specimens of laminated gabbro from the Centre 3 igneous complex, Ardnamurchan, was carried out by measuring orientations of grains of plagioclase, olivine, and augite with a Universal-stage. Linear alignments of primary precipitate mineral grains within the laminar fabrics were revealed by plots of data for coexisting plagioclase and olivine or augite. The plagioclase grains involved have tabular forms elongated parallel to their a-axes (rather than their c-axes). The olivine grains have flattened ovoid forms and the augite grains have sub-ophitic forms developed about prismatic primocrysts. In all specimens plagioclase displayed alignment of long grain-axes directed approximately down the dip of the lamination, save for one case in which a weak oblique alignment was observed. These lineations were reproduced by accompanying olivine and augite. The alignments are tentatively ascribed to flowage of a viscous boundary zone to the magma body in which crystal growth was taking place.
Hibonite and coexisting zoisite and clinozoisite in a calc-silicate granulite from southern Tanzania
Authors: Maaskant P. , Coolen J. J. M. M. M. , Burke E. A. J.
Published: December 2006

The third terrestrial occurrence of hibonite is reported from granulite-facies rocks in the Furua Granulite Complex in southern Tanzania. The mineral forms yellowish-brown lath-shaped crystals in a grossular-anorthite rock containing subordinate sphene (clino)zoisite, hercynite, apatite, ilmenite, and corundumilmenite intergrowths.

Electron-microprobe analyses indicate a generalized formula (Ca1−xREx)[(Al,Fe3+)12−2a+x(Ti,Si)(Ti,Si)a−x(Fe2+, Mg)a]O19, with RE = Ce + La + Nd, x = 0.2, and a = 0.8. Individual mineral analyses show a cation substitution of Ca + Ti + Fe3+ = RE + 2Al. Relatively high RE and Fe contents represent the main chemical differences with meteoritic hibonite. The hexagonal unit cell has a = 5.61 Å, c = 22.18, in good agreement with the other terrestrial hibonites.

Three compositional types of (clino)zoisite are distinguished: 1.8–3.1 wt% Fe2O3 (orthorhombic and monoclinic), 3.9–6.0 wt% Fe2O3 (monoclinic), and 5.8–7.9 wt% Fe2O3 with an average of 6.3 wt% RE2O3 (monoclinic).

Thermometric and barometric data for coexisting pyroxenes and garnet from adjacent rocks indicate granulite-facies equilibration conditions of 750 to 850 °C and 6 to 11 kb. During retrogression with increasing partial H2O pressures, hibonite reacted with plagioclase and garnet to form spinel, sphene, and RE-bearing clinozoisite. Corundum-ilmenite inter-growths probably resulted from the breakdown of an Fe-högbomite.
Zoisite-clinozoisite relations in low- to medium-grade high-pressure metamorphic rocks and their implications
Authors: Enami Masaki , Banno Shohei
Published: December 2006

Coexisting zoisite and clinozoisite in seventeen specimens from six localities in Japan have been studied with the electron-probe microanalyser. Zoisite and clinozoisite are commonly zoned, but compositional gaps between them are systematic. Referring to the metamorphic grade of the host rocks, a temporary and schematic phase-diagram for the system Ca2Al3Si3O12-(OH)-Ca2Al2Fe3+Si3O12(OH) is presented. With increasing temperature, in the range of low- to medium-grade metamorphism, the compositional gap between the two epidote-group minerals shifts towards higher Fe3+ compositions.
The eosphorite-childrenite series associated with the Li-Mn-Fe phosphate minerals from the Buranga pegmatite, Rwanda
Authors: Fransolet A.-M.
Published: December 2006

From the Buranga pegmatite, Rwanda, three occurrences of eosphorite-childrenite series minerals are described in assemblages of Li-Fe-Mn-bearing phosphates and in relationship with quartz-feldspar masses in close association with these assemblages.

Electron-microprobe analyses of these terms (Mn,Fe) AlPO4(OH)2 · H2O afford the following Fet/(Fet + Mn) ratios: 0.548, 0.341, and 0.200. However, thanks to an investigation of the refractive indices and pleochroism, the presence of ferric iron is demonstrated and an oxidation phenomenon, similar to that previously known in rockbridgeite, is suggested to explain the existence of oxidized eosphorite. The oxychildrenite problem is raised again.

The Fet/(Fet + Mn) ratios characterizing the eosphorite sensu lato would be correlated with the Fe and Mn content of the associated major phosphates, the chemical analyses of which are also provided. The investigation of the structural relationships shows that eosphorite might form a paragenesis with montebrasite and that these phosphates replace Na- or K-feldspars by a hydrothermal process. Owing to the apparent dependence of the chemical properties of the couple eosphorite-montebrasite on those of the earlier-formed phosphates, it seems likely that the formation period of eosphorite-childrenite series minerals was prior to the oxidation and ferrisickleriteheterosite formation.
Continuity in the monazite-huttonite series
Authors: Kucha Henryk
Published: December 2006

Electron diffraction and electron-microprobe investigations have revealed the presence of order in the monazite-huttonite series. Chemical analyses from the literature and electron-microprobe analyses in this study show that the monazite-huttonite series, REPO4-ThSiO4, is only continuous if the contribution of F, M2+, and OH to the charge balance is taken into account. The electron-diffraction study points to ordered domain structures in the series.
A further study of analcime solid solutions in the system NaAlSi3O8-NaAISiO4-H20, with particular note of an analcime phase transformation
Authors: Kim Ki-Tae , Burley B. J.
Published: December 2006

The stability field of analcime solid solutions in the system NaAlSi3O8-NaAlSiO4-H2O has been previously determined by Kim and Burley (1971a). These experiments are re-examined with a view to determining the variations of the room-temperature cell parameters of analcime as a function of temperature of synthesis and composition. It is shown from this evidence that most of the analcime solid solutions in these experiments are equilibrium compositions. The increase in the cell dimension of quenched analcime solid solution is found to be 5 × 10−5 Å/°C. It is suggested that birefringence in analcime is induced by low water-pressure relative to total pressure. A phase transition appears to be observed in quenched analcimes of this study and is thought to be the same as that in the Golden analcime reported by Yoder and Weir (1960).
Contact metamorphism and fluid movement around the Easky adamellite, Ox Mountains, Ireland
Authors: Yardley Bruce W. D. , Barry Long C.
Published: December 2006

Contact metamorphism in the aureole of the Easky adamellite produced andalusite at the expense of regional staurolite, kyanite, and garnet. In the inner aureole sillimanite and K-feldspar also grew. Cordierite is only rarely present. Conditions of metamorphism in the inner aureole have been deduced from five independent criteria as 595 ± 30 °C and 2.5 ± 0.5kb. The nearby Lough Talt adamellite was emplaced at slightly higher pressures. Some aureole rocks have undergone oxidation with conversion of regional garnet to magnetite and andalusite. The reacting assemblage buffered ƒO2 near 10−17 bars. It is inferred that oxidation was caused by movement of H2O from the country rocks into the intrusion.
Duhamelite, Cu4Pb2Bi(VO4)4(OH)3.8H2O, a new Arizona mineral
Authors: Williams S. A.
Published: December 2006

Found by J. E. DuHamel, at a prospect near Payson, Arizona, where it occurs with chrysocolla, malachite, rare fornacite, wulfenite, and bismutite. Colour chartreuse green (RHS 1A), H = 3, D = 5.80. Pleochroism in yellow weak; α = 2.08, β = 2.11. Crystals are minute orthorhombic fibres a = 7.49 Å, b = 9.66, c = 5.87, Z = 1, Dcalc 5.99 g/cm3. Strongest lines: 5.014(4), 4.828(3), 3.493(5), 3.159(7), 2.950(10), 2.642(9), 1.870(3), 1.755(3). Wet analysis (avg. of 3) gave CuO 20.4%, PbO 28.4, Bi2O3 15.9, V2O5 23.1, H2O 11.8.
The metasomatic development of zoned ultramafic balls from Fiskenaesset, West Greenland
Authors: Fowler M. B. , Williams H. R. , Windley B. F.
Published: December 2006

This paper presents new data on the metasomatic development of zoned ultramafic balls from Fiskenaesset, West Greenland. Field and petrographic evidence indicate retrogression of original ultrabasic inclusions in acid country rock gneisses to serpentinemagnesite assemblages, followed by regional metamorphism and consequent development of the zonal structure upon metasomatic re-equilibration via a supercritical aqueous fluid phase confined to grain boundaries. The balls show varying degrees of deviation from an ideal sequence (antigorite-talc-tremolite-hornblende-chlorite-country rock) intimated by non-equilibrium thermo-dynamics, the currently accepted conceptual framework for the discussion of diffusion metasomatism.

Major and trace-element variations behave in a similar manner to those reported from other zoned ultramafic balls but fail to define the original country rock ultrabasic discontinuity unambiguously. It is tentatively suggested that application of the apparently systematic deviations from ideality may provide additional evidence.

The presence of a hornblende zone and absence of a continuous biotite zone are two significant differences from other zoned ultramafic bodies. The former may suggest increased mobility of the aluminium species at Fiskenaesset, the latter a lower temperature of formation or smaller K2O content of the gneissic hosts.
The composition of solid inclusions and the occurrence of shortite in apatites from the Tororo carbonatite complex of eastern Uganda
Authors: Aspden J. A.
Published: December 2006

Apatite concentrates obtained from a carbonatite of the Tororo complex contain cogenetic fluid and solid primary inclusions. The solid inclusions are commonly composed of calcite and shortite and these minerals, together with the host apatite, were deposited from aqueous fluids at approximately 400°C.
Pyribole structure types
Authors: Chisholm J. E.
Published: December 2006

A set of pyribole structures can be derived from a model I-beam containing two distinct silicate chains in which the tetrahedra are rotated by different amounts. The model allows some tetrahedral distortion and is not bound by the parity rule (Thompson, 1970). A subset of pyribole structures which includes all the commonly occurring types can be defined using a new rule: that the structure may contain two types of tetrahedral layer, but no tetrahedral layer may contain two types of tetrahedral chain. This rule is more fundamental than the parity rule and has its origin in the optimization of the edge-to-edge packing of the tetrahedral chains into layers. Pnm21 (amphibole) and Pbc21 (pyroxene) emerge as space groups for ‘low protopyriboles’. The approach used here leads naturally to the − and × -chains notation of Thompson used by Veblen and Burnham (1978).
Columbite from the Carrock Fell tungsten deposit
Authors: Beddoe-Stephens B. , Fortey N. J.
Published: December 2006

Minute crystals of columbite occur in tungstate ore in the quartz veins at Carrock Fell Mine. Accompanying wolframite crystals show pronounced niobium enrichment adjacent to growth faces. The columbite grains, however, occur as inclusions in minerals formed during metasomatic replacement of the wolframite. They are chemically variable, containing 7–18 % WO3 by weight, up to 1.9% Sc2O3, and up to 4.7% TiO2. Tin, a common minor element in columbite, was not detected. The columbite grains are spatially associated with carbonate minerals involved in wolframite replacement, and it is suggested that their formation occurred principally when carbonate precipitation caused a reduction in the stability of dissolved niobium complexes.
Orientation and geometry of the thomsonite unit cell: a re-study
Authors: Nawaz Rab , Malone John F.
Published: December 2006

New X-ray and optical studies show that thomsonite has a < b < c and its optical orientation is α = b, β = c, and γ = a. The refined cell dimensions of Old Kilpatrick thomsonite are a = 13.051, b = 13.092, and c = 13.263 Å. The systematic absences h+l odd for h0l, h + k odd for odd for hk0, and l odd for 0kl uniquely determine the space group as Pcnn for which the arrangement of the alumino-silicate framework is suggested. The exceptions to the above absences are the 704 reflection (due to Renninger effect) and many weak hk0 reflections which suggest that the space group might be Pcnm or Pcn2. The observed habit, cleavage, and parallel growth are discussed in the light of the proposed framework structure.
Native antimony and bournonite intergrowths in galena from the English Lake District
Authors: Stanley Chris J. , Vaughan David J.
Published: December 2006

The Driggith vein is representative of the lead-zinc mineralization in the Caldbeck Fells area, with a primary mineral assemblage consisting of quartz, baryte, calcite, chalcedony, pyrite, arsenopyrite, galena, sphalerire, bournonite, argentian tetrahedrite, and native antimony. Broadly similar assemblages are found in Pb-Zn mineralization of Upper Devonian to Permian age else-where in the Lake District. The paragenetic sequence appears to have been early pyrite and minor arsenopyrite associated with quartz; with later baryte, calcite, sphalerite, and chalcopyrite enclosed by galena. Within the galena occur inclusions of tetrahedrite, bournonite, and native antimony. A later stage of baryte mineralization was followed by the alteration of primary sulphides to secondary minerals. Elsewhere in the Lake District, galena occurring in this association also contains inclusions of native antimony, bournonite, and other sulphosalts, and in this respect differs from galena associated with earlier veins composed dominantly of chalcopyrite, pyrite, and arsenopyrite. The inclusions make a major contribution to the high antimony values reported in trace element analyses of galena from the Lake District. The occurrence of these inclusions, which in some cases display preferred orientation within the host galena, is discussed in terms of phase relations involving PbS and AgSbS2.
Strontian melilite in a nephelinite lava from Etinde, Cameroon
Authors: Fitton J. G. , Hughes D. J.
Published: December 2006

Strontium-rich (up to 16 wt% SrO) melilite occurs as microphenocrysts in a nosean-leucite-nephelinite lava from Etinde, Cameroon. Electron microprobe analyses show that the melilite is very strongly zoned with Sr, Fe, and Na enrichment towards the crystal rims. Sodium melilite and sodium ferrimelilite are the dominant end-member molecules and together account for up to 76 mole%. The crystals are optically negative and strongly birefringent with birefringence ranging from 0.014 in the cores to 0.032 at the crystal rims. Refractive indices measured at the rim of one crystal gave ω = 1.656, ɛ = 1.628. The cell dimensions of strontian melilite are a = 7.765Å, c = 5.054Å.
Cosmochlore—a new examination
Authors: Couper A. G. , Hey M. H. , Hutchison R.
Published: December 2006

Examination of cotype cosmochlore from the Toluca meteorite confirms Laspeyres's observations (1897) in every respect, except that what he determined as iron was largely titanium. His data are completed by an electron-probe analysis and by full optical and X-ray data. Accepting the identity of cosmochlore and ureyite, the optical data of Frondel and Klein (1965) for the latter are partly in error or misprinted.
Gahnite and columbite in an alkali-feldspar granite from New Zealand
Authors: Tulloch A. J.
Published: December 2006

Gahnite and columbite with compositions (Zn5.96Fe1.55Mg0.21Mn0.13)Σ7.85Al16.09O32and (Nb7.36Ta0.60Mn2.95Fe0.98Ti0.09)Σ11.98O24occur as accessory phases in a highly evolved garnetiferous muscovite alkalifeldspar granite. Both phases have developed as a result of a concentration of Zn, Nb, and Ta during the fmal stages of the fractional crystallization which led to the formation of the pluton, and the lack of a major mafic mineral such as biotite, in which these elements are normally camouflaged in granitoid rocks.
Garnet zoning and re-equilibration in the Strontian area, Scotland
Authors: Tyler I. M. , Ashworth J. R.
Published: December 2006

In Moinian metasediments regionally metamorphosed to sillimanite grade, garnet has subsequently been re-equilibrated in the inner (cordierite-potash feldspar) zone of the aureole of the Strontian Granodiorite. Zoning profiles of garnet from the aureole, and from surrounding regional assemblages, show retrograde Mnrich rims. Some regional garnets are also internally zoned. In the aureole as a whole, the partition measure for Fe and Mg between garnet and biotite shows a correlation with that for Ca between garnet and plagioclase. If interpreted in terms of a simple equilibrium model, this might suggest that pressure decreased with increasing temperature towards the granodiorite, but the trend can more plausibly be attributed to deviation from ideal solid-solution behaviour of Ca in garnet and plagioclase, with incomplete homogenization of garnet as a complicating factor in the outer parts of the aureole. From the difference in the temperature thresholds for garnet core equilibration, the timescale t2 of the thermal event relative to the regional t1 is estimated as t2/t1 ≅ 10−1.1±0.7, consistent with emplacement of the intrusion at an early stage of regional cooling.
Upper-mantle metasomatism beneath a continental rift: clinopyroxenes in alkali mafic lavas and nodules from Sruth West Uganda
Authors: Lloyd F. E.
Published: December 2006

Clinopyroxenes are dominant in highly potassic, silica undersaturated mafic volcanics occurring on the western rim of the uplifted, rifted East African craton. A kimbcrlite style of eruption provides nodules of alkali clinopyroxenite (clinopyroxene + titaniferous phlogopite+titanomagnetite, apatite, sphene, and rare corroded olivine) which have similar bulk chemistry to the feldspathoid-bearing lavas. Many nodules display metasomatic textures supporting a formation from the alteration of pre-existing material; clinopyroxene growth is characterized by complex, non-oscillatory colour zoning. Comparison of natural clinopyroxene chemistry with published data for elinopyroxenes crystallized from synthetic potassium-rich mafic material, suggests that a significant proportion of the nodules crystallized at upper-mantle pressures. Neither garnet- nor orthopyroxene-bearing nodules have ever been recorded from south-west Uganda, suggesting that metasomatism of the local mantle has proceeded far enough to obliterate all recognizable remnants of four-phase lherzolite.
The crystal chemistry and paragenesis of honessite and hydrohonessite: the sulphate analogues of reevesite
Authors: Bish D. L. , Livingstone A.
Published: December 2006

Honessite and hydrohonessite from Unst, Shetland, and Linden, Wisconsin, are sulphate-containing members of the pyroaurite group and are analogous to reevesite. The structural formula can be written (Ni5.55Mg0.10Fe2.353+)(OH)16(SO4)1.18.xH2O for the Unst material, with sulphate groups replacing the interlayer carbonate groups in reevesite. Microprobe analyses of the Unst material show amounts of SO3 in excess of that required to balance all trivalent cations and this may be due to the presence of an amorphous nickel sulphate material. We find no evidence for the presence of trivalent nickel in honessite.

The Unst material occurs in both 8.8 (honessite) and 11.1 Å (hydrohonessite) forms, depending on composition, humidity, and temperature, similar to carrboydite, motukoreaite, and SO4-exchanged takovite. The Wisconsin material occurs only with an 8.8 A basal spacing. The increase from the 7.7 Å basal spacing of reevesite is due to the difference in molecular geometry of carbonate and sulphate groups. The presence of the sulphate molecule is unambiguously shown by the infra-red spectra, and the observed bands are consistent with the sulphate groups lying in the interlayer with their trigonal axes parallel to c. The Unst material is found intimately mixed in variable proportions with reevesite, distributed in patches on chromite, and the mixed nature is revealed by X-ray powder diffraction, by variations in total SO3 content, and by the presence of absorptions due to both SO2-4 and CO2-3 in the infra-red spectra.
Mountkeithite, a new pyroaurite-related mineral with an expanded interlayer containing exchangeable MgSO4
Authors: Hudson D. R. , Bussell M.
Published: December 2006

Mountkeithite [(Mg,Ni)9(Fe3+,Cr,Al)3(OH)24]3+[(CO{in3,SO4)1.5(Mg,Ni)2(SO4)2(H2O)11]3− occurs with pyrite, magnetite, magnesite, hexahydrite, and morenosite in a low-temperature hydrothermal vein system in the Mount Keith disseminated nickel sulphide deposit, Western Australia. Electron-microprobe analyses gave the following average composition: MgO 31.7, NiO 6.1, CuO 0.1, Cr2O3 6.1, Fe2O3 8.3, Al2O3 2.6, SO3 14.7; microanalysis for C and H gave CO2 3.9, H2O 30.6; total 104.1. The X-ray powder diffraction pattern has the following strongest lines: 11.30(10), 5.63(8), 4.63(2), 3.765(6), 2.645(4), 2.545(4), 1.554(5), and 1.505(3); these can be indexed on a hexagonal cell with a = 10.698 Å, c = 22.545 Å.

Mountkeithite occurs as friable aggregates and rosettes composed of soft, pearly to translucent, pale pink to white flakes with perfect basal cleavage. Optical properties are uniaxial negative with ɛ = 1.51 and ω = 1.52; weakly dichroic from colourless to palest pink. Specific gravity is 2.12 (calc. 1.95). Mountkeithite is soluble, with efferves-cence, in dilute HCl. Mountkeithite changes to a pyroaurite-like phase, with a 7.8.Å basal spacing when immersed in water, but can be changed back to an 11.3 Å phase by immersion in 1M MgSO4; mountkeithite also collapses to a 7.8 Å basal spacing under vacuum. Phases similar to mountkeithite have been synthesized by immersing grains of stichtite in 1M MgSO4, at 20, 50, 105, and 200°C.

The structure of mountkeithite is interpreted as consisting of positively charged brucite-like hydroxyl layers, containing both divalent and trivalent cations, separated by about 7 Å-thick, negatively charged interlayers containing carbonate and sulphate anions, magnesium sulphate, and water. Carrboydite, motukoreaite, and hydrohonessite are minerals with similarly large basal spacings of 10–11 Å, and are also believed to have pyroaurite-related structures with expanded interlayers.
Atomic arrangements on the twin boundaries of orthoclase twins
Authors: Wooster W.A.
Published: December 2006

In the extensive literature dealing with the growth twinning in crystals, two approaches have been followed. Friedel (1926) related twinning to a lattice common to both parts of the twin, while others have considered how the atoms at the junction must be packed to give substantially the same interatomic distance and bond angles as in the Z single crystal. The second approach has been adopted in this paper.

This investigation has been carried out by constructing ball-and-spoke models of the various twins. The balls constituting the boundary between the two parts of the twin have been drilled to accord with the full symmetry of the twinned crystal, while the rest of the model has the normal symmetry of the untwinned crystal. The orientation of the two sets of crystallographic axes is determined by the twin law. Only when it was possible to construct a model in which the environment of the boundary balls closely approximated to the normal environment, was the proposed atomic arrangement accepted.
New determinations of tin and tungsten in granites from south-west England
Authors: Alderton D. H. M. , Moore F.
Published: December 2006

Recent studies on the development of Sn-W mineralization in south-west England (Sheppard, 1977; Simpson et al., 1979; Jackson et al., 1979) indicate that the hydrothermal fluids dominantly consisted of local meteoric waters. These waters were heated up and drawn into the granite in a convective hydrothermal system. It is proposed that the fluids leached Sn and W from minerals such as the dark micas, during their passage through the granite. These metals were then deposited in veins at higher levels in the system.