bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zoisite-clinozoisite relations in low- to medium-grade high-pressure metamorphic rocks and their implications
Authors: Enami Masaki , Banno Shohei 
Published: December 2006

SummaryCoexisting 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

SummaryFrom 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

SummaryElectron 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

SummaryThe 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

AbstractContact 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

AbstractFound 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

AbstractThis 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

AbstractApatite 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

AbstractA 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

AbstractMinute 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

AbstractNew 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

AbstractThe 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

AbstractStrontium-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

AbstractExamination 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

AbstractGahnite 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

AbstractIn 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

AbstractClinopyroxenes 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

AbstractHonessite 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

AbstractMountkeithite [(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.
A review of the geochronology of the Precambrian of Saskatchewan—some clues to uranium mineralization
Authors: Bell Keith 
Published: December 2006

AbstractAssessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.