bluuebunny/crossref_metadata_2025_split huggingface dataset:
Re-examination of kirwanite: a ferri-ferro-hornblende from Co. Down, Northern Ireland
Authors: Nawaz Rab , Ryback George 
Published: December 2006

AbstractX-ray powder, optical, infrared, and chemical data suggest that kirwanite is an amphibole of composition (Na,K)0.10Ca1.80(Fe2+,Mn)3.10Mg0.79Fe1.143+Al0.78Si7.18O22(OH)2 and thus corresponds to ferri-ferro-hornblende (Leake, 1978). The type locality, originally given as the NE coast of Ireland, is most likely Dunmore Head, Co. Down. Kirwanite occurs in the groundmass and the vesicles of variolitic andesite dykes of the Mourne dyke swarm. Thomson's original analysis of kirwanite was probably made on a mixture and the name should not be used for an amphibole species.
Non-metamict uranoan pyrochlore and uranpyrochlore from tuff near Ndale, Fort Portal area, Uganda
Authors: Hogarth D. D. , Horne J. E. T. 
Published: December 2006

AbstractA thin (100 m) cover of flat-lying, Recent, calcite-rich tuff at Ndale near Fort Portal, Uganda, unconformably overlies steeply dipping Precambrian metamorphic rocks. It is locally radioactive owing to uranium-rich pyrochlore minerals and lesser amounts of zircon, monazite, titanite, and an unidentified thorium phosphate. In one concentrate, four grains of uranpyrochlore and one grain of uranoan pyrochlore showed a positive linear correlation of Ti with U, and negative linear correlations of Ti with Na, F and Sr. Ta remained high and relatively constant [11 anal., ave. 14.5 (0.6)% Ta2O5]. In the same concentrate the composition of a separate grain of uranoan pyrochlore did not plot on these lines and Ta was comparatively low [2 anal., ave. 4.5 (0.3)% Ta2O5]. The data suggest two separate paths of differentiation. However, zoned grains were not observed. Unit cells were cubic with a = 10.351 ± 0.002 Å for a grain with 12.9% UO2tot and 10.333 ± 0.002 Å for a grain with 26.6% UO2tot. On heating in air the cell size decreased, possibly due to oxidation of U4+. The crystalline nature of these minerals can be attributed to a very young (4000–5000 yr) geological age.
Petrology and geothermometry of the Little Michiru Complex, Malawi
Authors: Morel S. W. 
Published: December 2006

AbstractThe Little Michiru complex is a composite intrusion of pyroxenite and pyroxene syenite which is located at the boundary between amphibolite and granulite facies gneisses in the Shire rift valley. Pyroxene and feldspar chemistry shows that the intrusion consolidated from two magmatic fractions, one a pyroxenite cumulate that equilibrated at 870–1000 °C, the other a partly anatectic pyroxene syenite magma which metasomatized the surrounding gneisses during granulite-facies metamorphism and equilibrated at a temperature of 730–830 °C at 7 kbar.
Yimengite of K–Ti metasomatic origin in kimberlitic rocks from Venezuela
Authors: Nixon Peter H. , Condliffe Eric 
Published: December 2006

AbstractThis second recorded occurrence of yimengite, K(Cr, Ti, Fe, Mg, Al)12O19, is in a Precambrian kimberlitic sill in the Guaniamo District of Bolivar Province, Venezuela. The paragenesis is similar to that of the type area in Shandong Province, China, where the mineral is in kimberlite dykes. At both localities the yimengite is a K, Ti-bearing metasomatic product of chromium-rich spinel. In the Venezuela rocks the spinels are of the type occurring both as diamond inclusions and as a component of diamond-related Cr-rich garnet harzburgite mantle xenoliths. Yimengite contains significant amounts of barium (up to 3.4wt.% BaO) and is thus transitional to the recently described mineral hawthorneite, Ba(Cr, Ti, Fe, Mg)12O19. Both members are part of a suite of titanate minerals found in kimberlites and their inclusions which has been described by Haggerty and coworkers; they formed as a result of mantle metasomatism generated by K- and Ba-rich fluids. In Venezuela, metasomatism of this type would appear to be deeper than that usually recorded, namely in the basal lithosphere. The metasomatizing fluids are derived from the underlying, more oxygenated asthenosphere. The host kimberlitic rocks are not significantly enriched in K and Ba, but these elements are concentrated in later micaceous dykes which are conjectured to have been generated within similar metasomatized mantle.
On the reported presence of potassium in clinopyroxene from potassium-rich lavas: a transmission electron microscope study
Authors: Mellini M. , Cundari A. 
Published: December 2006

AbstractTitanian aegirine in a pegmatoid differentiate from leucitite sensu stricto (i.e. without modal plagioclase) was found to contain significant K (up to 0.07K atoms per formula unit; 0.11 wt.% K2O) by electron probe microanalysis. A transmission electron microscope study showed that this pyroxene contained a lamellar amorphous phase and other more irregular, amorphous domains where K and Al are concentrated. The microstructures suggest that the aegirine-amorphous phase system did not achieve textural equilibrium. Also, the chemistry of this phase is variable, particularly in Ca and Mg, suggesting lack of chemical equilibrium within the liquid from which the phase derived. The average composition of the latter approaches that of the coexisting K-richterite and is interpreted as trapped residual liquid, i.e. glass, from pyroxene crystallization which failed to develop a crystalline amphibole. In view of the extensive stability of richterite coexisting with pyroxene to high pressure, the reported occurrence of ‘K-bearing pyroxene’ may not be considered as a homogeneous K-bearing phase and a predictable potassium carrier in the petrogenesis of K-rich rocks like leucitites and lamproites.
Ternary feldspars: two-feldspar assemblages at P(H2O) = 5 kbar
Authors: Jones Rhian H. 
Published: December 2006

AbstractIn a study of the liquidus surface in the silica-undersaturated part of the system Q-An-Ne-Ks at P(H2O) = 5 kbar, several two-feldspar plus liquid assemblages were obtained. The compositions of the feldspars were determined by electron microprobe analysis. The products of short runs (one or two days) consisted of fine intergrowths of two feldspars which may have crystallized during the heating period, or in the early stages of the run. Runs of four days were of sufficient length to coarsen these intergrowths such that individual euhedral crystals could be observed. However, analyses of the feldspar crystals from the longer runs showed a greater amount of ternary solid solution than expected. This may be attributed to the persistence of a small quantity of the second feldspar intergrown in the crystals. The slope of the tie-line joining one of the inferred pairs has been shown to be reproducible for gel and crystalline starting materials, hence the slopes of the tie-lines are believed to represent their equilibrium slopes.
The chemical stability of mimetite and distribution coefficients for pyromorphite–mimetite solid-solutions
Authors: Inegbenebor Adedayo I. , Thomas John H. , Williams Peter A. 
Published: December 2006

AbstractThe equilibrium solubility of mimetite has been determined in aqueous solution at 298.2K. For the reaction Pb5(ASO4)3Cl(s,mimetite)+6H+(aq)⇌5Pb2+(aq)+3H2AsO4−(aq)+Cl−(aq) at this temperature log KH+, extrapolated to zero ionic strength, is equal to −27.9(4). This value is equal, within experimental error, to that corresponding to pyromorphite, Pb5(PO4)3Cl, derived from the literature, and redetermined here under analogous conditions. Distribution coefficients in terms of both HXO42− and H2XO4−(aq) ions (X = P,As) have also been determined for solid phases of the pyromorphite-mimetite solid solution series containing from 5 to 95 mol. % mimetite. Although the two end-members are isostructural without being strictly isomorphous, the solid solution series behaves ideally over the whole compositional range; that is, the composition of the solid phase reflects the ratio of arsenate to phosphate species in aqueous solution at pH values corresponding to naturally-occurring aqueous solutions generally associated with the oxidized zones of base metal orebodies. Some relationships between mimetite and other secondary lead(II) and copper(II) arsenate minerals have been explored.
Thermal decomposition of Li8(Al6Si6O24)Cl2
Authors: Taylor D. 
Published: December 2006

AbstractLi8(Al6Si6O24)Cl2, a synthetic member of the sodalite family (Henderson and Taylor, 1977), was prepared by heating natural sodalite, Na8(Al- 6Si6O24)Cl2 (from Låven, Norway), in molten LiC1 at 800 °C for 2h, washing uncombined LiC1 from the product and drying at 110 °C Chemical analyses of the natural sodalite and the Li-sodalite are given in Table 1. The cell edge of the Lisodalite was 8.4476(9) Å (Si as internal standard: a = 5.43065/Å at 25 °C in good agreement with literature values (Henderson and Taylor, 1977).
A calcian analcime-bytownite intergrowth in basalt, from Skye, Scotland, and calcian analcime relationships
Authors: Livingstone A. 
Published: December 2006

AbstractWithin a reyerite-tobermorite (11 Å) amygdale assemblage in olivine basalt blocks, near Drynock, Skye, is a porcellaneous material which either lines or completely fills the amygdales (Livingstone, 1988). Electron-probe microanalysis combined with back-scattered electron imaging identifies individual components of the porcellaneous material as calcian analcime and bytownite, (An74-79). Back-scattered electron imaging reveals a second generation analcime pervading the calcian analcime-bytownite intergrowth and forming patches and discrete veinlets (Fig. 1A).
Unit cell dimensions of the hydrated aluminium phosphate–sulphate minerals sanjuanite, kribergite, and hotsonite
Authors: De Bruiyn H. , Beukes G. J. , Van Der Westhuizen W. A. , Tordiffe E. A. W. 
Published: December 2006

AbstractAT the time when the hydrated aluminium phosphate-sulphate hotsonite (Beukes et al., 1984a) and its equally rare relative zaherite (Beukes et al., 1984b; De Bruiyn et al., 1985) were discovered near Pofadder, South Africa, very little was known about the unit cells of the other two hydrated aluminium phosphate-sulphate minerals sanjuanite and kribergite, originally described by De Abeledo et al. (1968) from Argentina and Sweden, respectively. Although the Powder Diffraction file (PDF) contains the X-ray diffraction patterns for sanjuanite and kribergite (PDF 20-47 and 20-48 respectively), they had not been indexed nor have their unit cell parameters been calculated thus far.
Niobian K–Ba–V titanates from micaceous kimberlite, Star mine, Orange Free State, South Africa
Authors: Mitchell Roger H. , Meyer Henry O. A. 
Published: December 2006

AbstractCompositional data are presented for Nb-Ba-K-V titanates from micaceous kimberlite (Star mine, S. Africa). These data significantly extend the previously known range of solid solutions in naturally occurring members of the hollandite group. Two distinct suites of crystals occur. One is a suite of primary groundmass prismatic crystals that are Ba-K-V-rich and represent solid-solutions from the priderite series towards mannardite. The second suite consists of anhedral xenocrysts that are Ba-free. In this suite relatively Nb-rich varieties (>4.0% Nb2O5) represent solid-solution towards a niobian-bearing potassian analogue of mannardite, whereas relative Nb-poor (<3.0% Nb2O5) varieties are Nb-bearing vanadian priderites. These hollandite-group minerals have compositions that differ significantly from priderites found in lamproites.
Holtite, (Si2.25Sb0.75)B [Al6(Al0.43Ta0.27□0.30) O15 (O,OH)2.25]: crystal structure and crystal chemistry
Authors: Hoskins B. F. , Mumme W. G. , Pryce M. W. 
Published: December 2006

AbstractHoltite, (Si2.25Sb0.75)B[Al6(Al0.43Ta0.27□0.30)O15(O,OH)2.25], is orthorhombic a = 4.6914(5), b = 11.896(2), c = 20.383(4)Å, space group Pnma. Full-matrix least-squares refinement yielded a final R = 0.030, for 1664 reflections with I ⩾ 3σ(I). Its crystal structure is closely related to that of dumortierite, but with the difference that extensive substitution of Si by Sb occurs in holtite. SbO3 triangular pyramids replace the SiO4 tetrahedra arranged around the inside edge of the hexagonally shaped tunnels which are the feature of the dumortierite and holtite structures. Associated with these replacements is the replacement of Al by Ta in the octahedral site centred in these tunnels, and the development of vacancies in this metal site and its attached oxygens.
Time-dependent Landau theory for order/disorder processes in minerals
Authors: Carpenter M. A. , Salje E. 
Published: December 2006

AbstractRecent advances in the use of time-dependent order parameter theory to describe the kinetics of order/disorder transitions are reviewed. The time dependence of a macroscopic order parameter,Q, follows, to a good approximation:For systems in which the order parameter has a long correlation length (large ξ) and is not conserved (small ξC), the Ginzburg-Landau equation provides a general kinetic solution:Specific rate laws can be derived from this general solution depending on whether the crystals remain homogeneous with respect to the order parameter,Q. The advantages of the overall approach are, firstly, that it does not depend on the detailed structure of the material being examined; secondly, that the order parameter can be followed experimentally through its relationship with other properties, such as spontaneous strain, excess entropy, intensities of superlattice reflections, etc.; and, finally, that conventional Landau expansions inQmay be used to describe the thermodynamic driving forces.For a simple second-order transition in crystals which remain homogeneous inQthe rate law is:If the free energy of activation varies with the state of order of the crystal, this becomes:Simplifying assumptions can be introduced into the mathematics, or the integrals can be solved numerically. For crystals which remain homogeneous, the simplest solution valid only over small deviations from equilibrium is:For crystals which develop heterogeneities inQ, the rate laws change significantly and we find as an extreme case:where theAcoefficient may be temperature dependent.Experimental data available for a limited number of minerals (omphacite, anorthite, albite, cordierite and nepheline) are used to demonstrate the practical implications of the overall approach. As anticipated from the theory, modulated structures commonly develop during kinetic experiments, the observed rate laws depend on whether the critical point of the ordering is located at the centre or boundary of the Brillouin zone, and the rate laws for ordering and disordering can be quite different. The importance of different length scales, not only in the different techniques for characterizing states of order (IR, NMR, calorimetry, X-ray diffraction, etc.) but also for interpreting observed mechanisms and rate laws, is also outlined.Use of the order parameter in Landau expansions and in Ginzburg-Landau rate laws provides, in principle, a means of predicting the equilibrium and non-equilibrium evolution of minerals in nature.
Lead isotope and trace element variation in Tenerife pumices: evidence for recycling within an ocean island volcano
Authors: Wolff J. A. , Palacz Z. A. 
Published: December 2006

AbstractThree voluminous Quaternary phonolitic pumice fall deposits erupted from the compositionally-zoned Tenerife magma chamber exhibit variability in Sr and Pb isotope ratios. It has been previously argued that the Sr isotope variations are due to syn-eruptive interaction between magma and hydrothermal fluids (Palacz and Wolff, 1989). Pb compositions are not correlated with Sr, and are believed to reflect magmatic values. Pb isotope ratios exhibit regular variation with degree of fractionation, and one zoned deposit is heterogeneous in Pb. The highest values seem to characterize the most fractionated upper parts of the zoned system. This is unlikely to be a consequence of magmatic recharge. Isotopic and trace element behaviour is instead consistent with combined assimilation and fractional crystalliza- tion, involving the recycling of material containing relatively radiogenic Pb, from within the volcanic edifice. Assimilation of sediment intercalated within the submarine portion of the pile is ruled out by the isotopic data. The most probable contaminant is a felsic igneous rock. Early trachytes reported by Sun (1980) have the required Pb isotope compositions and may approximately represent the assimilant.
An apparatus for the study of fast precipitation reactions
Authors: Rickard David 
Published: December 2006

AbstractAn apparatus is described for the measurement of the rates of fast precipitation reactions. It consists of a T-tube, where reactants are added to the arms of the T, mixed rapidly at the junction, and the rates of disappearance of reactants or appearance of products are measured along the stem of the T. The geometry of the system results in a steady state being established in the apparatus, enabling detailed analysis of reaction progress. The apparatus has been used to investigate the kinetics and mechanism of iron sulphide precipitation reactions. It has enabled measurements to be made with relatively high precision and good accuracy of the first 130 ms of reaction time.
Bernardite, a new thallium arsenic sulphosalt from Allchar, Macedonia, with a determination of the crystal structure
Authors: Pašava J. , Pertlik F. , Stumpfl E. F. , Zemann J. 
Published: December 2006

AbstractThe new mineral bernardite has been identified on one specimen from Allchar, Macedonia, Yugoslavia, together with orpiment and realgar. It forms black crystals, the size of which may exceed 1 mm. The streak is deep red; on an arbitrarily oriented section R(589nm) ranges from 23.8 to 24.7% in air, from 10.2 to 11.6% in oil. Microprobe analyses together with an X-ray structure analysis suggest the ideal formula TlAs5S8, with a possible replacement of As by Sb up to 15 wt. %. Monoclinic; a 15.647(4), b 8.038(3), c 10.750(3) Å, β 91.27(3)°; space group P21/c; Z = 4; R = 0.049, wR = 0.036 for 2410 reflections. The atomic arrangement consists of a 3-dimensional As5S8 framework with eight-coordinated T1 in its holes. The mineral is named for Doc. Dr Jan H. Bernard, Prague, Czechoslovakia.
Fluid and mineral inclusions in corundum from gem gravels in Sri Lanka
Authors: de Maesschalck A. A. , Oen I. S. 
Published: December 2006

AbstractMineral and fluid inclusions were studied in seven gem corundums from gravels of three areas in Sri Lanka. All fluid inclusions are pure CO2. Microthermometry results on primary fluid inclusions suggest formation of corundum under granulite facies metamorphism (>630°C, 5.5 kbar). Secondary fluid inclusions indicate different retrograde events of post-metamorphic cooling and uplift for different source areas.
Deerite from Ile de Groix, Brittany, France
Authors: Dudek K. , Kienast J. R. 
Published: December 2006

AbstractDeerite has been found in layers of Fe-rich metasediments, metamorphosed under conditions of blueschist to eclogite facies (T = ca. 480°C). Geochemical comparisons with other deerites described in the literature show that the Ile de Groix deerites most closely resemble the Mn-poor, alpine type, and Sifnos deerites. The P-T conditions of the Ile de Groix metamorphism do not conform with the stability field of deerite. In the assemblages examined here deerite seems to be a relic from earlier stages of prograde metamorphism.
Mn-silicate skarns from the Gåsborn area, West Bergslagen, central Sweden
Authors: Damman Arend H. 
Published: December 2006

AbstractIn the Gåsborn area, West Bergslagen, central Sweden, Mn-silicate-magnetite-jacobsite skarns were formed as the result of three successive processes. (1) Deposition of exhalative-sedimentary manganiferous iron-ore-bearing sediments together with cherts and volcanics. (2) Intrusion of a synvolcanic anorogenic granite and some slightly younger gabbros and tonalites: under influence of these intrusives the manganiferous iron-ore-bearing sediments were metamorphosed into (a) rhodonite(I)-magnetite-pyrophanite-garnet assemblages; (b) (manganiferous) hedenbergite(I)-allanite-titanite-garnet-magnetite assemblages; (c) tephroite-jacobsite-pyrophanite-garnet assemblages and (d) magnetite-bearing quartzites. (3) Release of hydrothermal fluids from the granite and subsequent alteration of the above assemblages into metasomatic infiltration skarns, consisting of rhodonite(II), garnet, hedenbergite(II), biotite, actinolite or edenite (with up to 20.11 wt.% MnO), chlorite, bementite, fluorite, helvite, rhodochrosite, hematite, rutile and accessory galena, sphalerite, wittichenite, aikinite, pyrrhotite, chalcopyrite and pyrite.The maximum temperature (T) and pressure (P) during contact metamorphism are estimated at 550°C and 1.0 kbar respectively. The fluid under influence of which the metasomatic infiltration skarns were formed was relatively rich in Fe, Cl and F and carried little or no Mg and Mn.During early diagenesis (beginning of stage 2) fo2 was between the hematite/magnetite (hm/mt) and the hausmannite + hematite = jacobsite buffers (h + m = j). During stage 2, with increasing T, fo2 changed from above to below hm/mt. Magnetite and jacobsite at some distance from the hydrothermal veins from which the metasomatic skarn-forming fluids were released, were altered during stage 3 into hematite. Magnetite in, and close to the hydrothermal veins was not altered to hematite, implying an increase in fo2 to above hm/mt with increasing distance from these veins.
The cyclic unit beneath the UG1 chromitite (UGIFW unit) at RPM Union Section Platinum Mine—Rosetta Stone of the Bushveld Upper Critical Zone?
Authors: Eales H. V. , de Klerk W. J. , Butcher A. R. 
Published: December 2006

AbstractThe UG1 Footwall unit is a layered pyroxenite-norite-leuconorite-anorthosite sequence between the Middle Group 4 and Upper Group 1 chromitites of the Upper Critical Zone, and is c. 300 m thick at Rustenburg Platinum Mines, Union Section, where it shows an oscillatory fluctuation in whole-rock Mg/(Mg + Fe), Cr/Co, Ni/V and Fe/Ti ratios with stratigraphic height. This permits subdivision into 8 sub-cycles which match a subdivision based on cyclical variations in orthopyroxene and feldspar compositions. Constituent pyroxene grains of pyroxenites, norites and leuconorites alike contain rounded and embayed plagioclase inclusions in abundance. Sr-isotope disequilibrium prevails in some samples between the orthopyroxene and feldspar populations. Chemical and isotopic data support a model of pulsatory injection of limited volumes of a more primitive, mafic liquid into a resident column of depleted residua, from which sodic labradorite and Mg-poor bronzite were crystallizing. The depleted liquid is equated with the supernatant liquid residuum of buried cumulates (Sric. 0.7054) and the primitive liquid with magma parental to the UG1-UG2 lineage (Sri ⩾ 0.7068). The increase in leucocratic character of the 300 m column, with height, is attributed to the rising of low-density liquids enriched in the components of feldspar during separation of the pyroxenites. Deposition of the UG1 chromitite layers is attributed to mixing of a major influx of primitive liquid with a feldspathic residuum at the top of the UG1 Footwall unit. There is no evidence to indicate the participation of a discrete A-type liquid (Irvine and Sharpe, 1982) in this process.
Indium-bearing chalcopyrite and sphalerite from the Gåsborn area, West Bergslagen, central Sweden
Authors: Kieft Kees , Damman Arend H. 
Published: December 2006

AbstractIn the Gåsborn area, West Bergslagen, central Sweden, Fe-rich, indium-bearing (0.1–2.0wt.% In) sphalerite is replaced by Fe-poor sphalerite containing minute inclusions of chalcopyrite, roquesite and an unnamed In-Zn-rich phase. Fe-rich, In-bearing sphalerite is primary; indium occurs as a roquesite molecule in solid solution. Fe-poor sphalerite, roquesite, chalcopyrite and the unnamed In-Zn-rich phase were formed from In-bearing sphalerite by secondary processes, characterized by the so-called ‘chalcopyrite disease’.