bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monazite-huttonite solid-solutions from the Vico Volcanic Complex, Latium, Italy
Authors: Ventura Giancarlo Della , Mottana Annibale , Parodi Gian Carlo , Raudsepp Mati , Bellatreccia Fabio , Caprilli Enrico , Rossi Paolo , Fiori Salvatore 
Published: December 2006

AbstractThe crystal-chemical relationships occurring within a single grain of monazite-(Ce) from Vetralla, Vico Volcanic Complex, north of Rome, are outlined. The sample is from a miarolitic cavity in a holocrystalline ejectum consisting of K-feldspar plus minor plagioclase, mica and Fe-oxides, collected from a pyroclastic explosive level. The Gandolfi film (Cu-Kα radiation) can be indexed in space group P21/n with a = 6.816(4); b = 6.976(4); c = 6.471(3) Å; β = 103.63(3)°; V = 299.0(6) Å3. Electron-probe microanalyses plot within the field of monazite along the huttonite-monazite edge of the huttonite-monazite-brabantite triangle. Despite patchy and irregular zoning, the grain shows a clear enrichment towards pure monazite at the outer rim. A constant Th:Si ratio of 1:1 indicates the existence of a simple solid-solution between huttonite and monazite. The substitution can be written as Th4+ + Si4+ → REE3+ + P5+ without requiring any electrostatic compensation by divalent cations, or by anionic groups. The REE distribution pattern is compatible with that of monazites from syenitic rocks.
Recognition and significance of multiple fluid inclusion generations in telogenetic calcites
Authors: Muchez Philippe , Slobodnik Marek 
Published: December 2006

AbstractFerroan and non-ferroan calcites occur in fractures in the Lower Carboniferous of the Variscan foreland of southern Belgium. These fractures post-date the Variscan orogeny and the calcites have a telogenetic origin. The non-ferroan calcites formed by recrystallization of the ferroan calcites. Two types of monophase aqueous fluid inclusions are present in the ferroan calcite cement. Although both types of inclusions formed at a temperature not exceeding 50°C, one type contains a moderately saline fluid (3.6–16.3 eq. wt.% NaCl) and the other type fresh water (Tm ice = 0°C). The fluid inclusions in the non-ferroan calcite also contain fresh water.Detailed petrography of the fluid inclusions indicate that the fresh water migrated through the crystals along opened cleavage planes and microfractures. Therefore, they have a secondary origin. The recrystallization of the ferroan calcites to non-ferroan calcites occurred in this fresh water. The saline fluid inclusions are not related to the above mentioned microstructures and although their origin remains unknown, they could represent the ambient fluid from which the ferroan calcites precipitated. The study of the relationship between the occurrence of fluid inclusions and the microstructures seems promising for the identification of fluid inclusions representing post mineral formation fluid and temperature conditions in calcite cements.
Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope
Authors: Prior David J. , Trimby Patrick W. , Weber Ursula D. , Dingley David J. 
Published: December 2006

AbstractWe have developed a system using ‘forescatter detectors’ for backscattered imaging of specimen surfaces inclined at 50–80° to the incident beam (inclined-scanning) in the SEM. These detectors comprise semiconductor chips placed below the tilted specimen. Forescatter detectors provide an orientation contrast (OC) image to complement quantitative crystallographic data from electron backscatter patterns (EBSP). Specimens were imaged using two detector geometries and these images were compared to those collected with the specimen surface normal to the incident beam (normal-scanning) using conventional backscattered electron detector geometries and also to an automated technique, orientation imaging microscopy (OIM). When normal-scanning, the component of the BSE signal relating to the mean atomic number (z) of the material is an order of magnitude greater than any OC component, making OC imaging in polyphase specimens almost impossible. Images formed in inclined-scanning, using forescatter detectors, have OC and z-contrast signals of similar magnitude, allowing OC imaging in polyphase specimens.OC imaging is purely qualitative, and by repeatedly imaging the same area using different specimen-beam geometries, we found that a single image picks out less than 60% of the total microstructural information and as many as 6 combined images are required to give the full data set. The OIM technique is limited by the EBSP resolution (1–2°) and subsequently misses a lot of microstructural information. The use of forescatter detectors is the most practical means of imaging OC in tilted specimens, but it is also a powerful tool in its own right for imaging microstructures in polyphase specimens, an essential asset for geological work.
Two new occurrences of benleonardite, a rare silver-tellurium sulphosalt, and a possible new occurrence of cervelleite
Authors: Spry Paul G. , Thieben Scotf E. 
Published: December 2006

AbstractBenleonardite, ideally Ag8(Sb,As)Te253, occurs in ore specimens from the Mayflower and Gies epithermal gold-silver telluride deposits in Montana commonly spatially associated with hessite and tetrahedrite. In these deposits, it is Cu-bearing (up to 2.7 wt.%) and exhibits a slight deficiency in Ag+Cu coupled with a slight excess in S. A cervelleite-like mineral coexists with benleonardite at Mayflower and is unusual in composition in that it is Se-bearing suggesting the possibility of solid solution with aguilarite (Ag4SeS).
The crystal structure of frankamenite
Authors: Rozhdestvenskaya I. V. , Nikishova L. V. , Lazebnik K. A. 
Published: December 2006

AbstractFrankamenite, K3Na3Ca5[Si12O30]F3(OH)1H2O, from the Yakutian charoitic rocks, has a triclinic unit cell with the dimensions: a = 10.094(3), b = 12.691(3), c = 7.240(1) Å, α = 90.00(2)°, β = 111.02(2)°, γ = 110.20(2)°, sp.gr. = P1, Z = 1. Its crystal structure has been refined to Raniso= 0.059 (Rw = 0.060) using the intensities of 2563 reflections.The bases of the structure are zig-zag walls of Ca, Na octahedra joined by infinite octagonal cross-sectioned tubes of SiO4 of the composition (Si12O30). Unlike canasite from the Khibini Mountains, the triclinic cell of frankamenite contains only one silicate tube. The atomic coordinates, interatomic distances and angles are topologically similar to those of canasite. Major differences are observed in the distribution of octahedral cations, which reflect the different anion compositions. Frankamenite exhibits six mixed Ca-Na positions, whereas canasite has only one such position. The H2O molecule is located in the centre of the silicate tube between K+ cations.
Compositional Variation of pyroxene and mica from the Little Murun ultrapotassic complex, Aldan Shield, Russia
Authors: Mitchell Roger H. , Vladykin Nikolai V. 
Published: December 2006

AbstractPyroxene and mica found in plutonic rocks of the Little Murun ultrapotassic pluton exhibit trends of compositional evolution that permit evaluation of the differentiation sequence of the complex. Pyroxene evolves from diopside in kalsilite and phlogopite pyroxenites through aegirine-diopside in shonkinite to aegirine in late stage charoitite and evolved hypabyssal rocks. The compositional trend is unusual in that the hedenbergite content of the pyroxenes never exceeds 15 mol.% and is thus unlike pyroxene compositional trends found in sodic alkaline complexes. Mica is Al- and Ti-poor and ranges in composition from Fe-rich phlogopite through biotite towards tetraferriannite. Compositional trends of mica found in ‘lamproite-like’ hypabyssal rocks are identical to those observed in the micaceous plutonic rocks; hence the former are considered to be representatives of the lamprophyric facies of the magmas which formed the plutonic series.
Sericitization of plagioclase in the Rosses Granite Complex, Co. Donegal, Ireland
Authors: Que Meideno , Allen Alistair R. 
Published: December 2006

AbstractSericitization in three separate pulses of the Rosses Granite Ring Complex, Co. Donegal, Ireland, has been investigated texturally and chemically using electron microscopy, electron microprobe and fluid inclusion thermometry. The sericitization, which is restricted to the cores of plagioclase, is associated with pores which are abundant in the cores, but absent in the margins. Alkali feldspar, although porous, is unaltered. Associated with the sericitization is alteration of the adjacent primary plagioclase within the cores of grains to a more sodic composition.It is postulated that the sericitization resulted from the action of externally derived secondary hydrothermal fluids, which gained access to the pores in the plagioclase via now sealed microfractures, formed either by contraction during cooling of the Rosses Complex, or more likely by hydraulic fracturing by the fluids themselves. Limited fluid/rock ratios restricted the degree of sericitization within the host plagioclase, whilst an absence of alteration in alkali feldspar may have been due to the inaccessibility of pores in the alkali feldspar to the hydrothermal fluids at the time of alteration. Fluid inclusion data suggest that the fluids were of low salinity, and that the sericitization took place at an early stage in the cooling history of the Rosses Complex at temperatures between 400 and 600°C. It is further contended that greisenization in the Rosses Complex predated the sericitization and that the greisenization may have been due solely to volatile-rich late-stage magmatic fluids.
Thermal expansion of cancrinite
Authors: Hassan Ishmael 
Published: December 2006

AbstractThermal expansion coefficients were measured for a cancrinite from Bancroft, Ontario, Canada. Measurements of cell parameters and unit-cell volumes were obtained at room temperature and at heating intervals of 50°C over the temperature range from 50 to 1400°C. The unit-cell parameters for cancrinite increase non-linearly with temperature up to 1200°C and shortly thereafter, the mineral melted. The c parameter increases more rapidly than the a parameter, and the c/a ratio increases linearly with temperature. A plausible thermal expansion mechanism for cancrinite, which is based on the framework expansion that occurs as a function of cavity content, is presented. In the thermal expansion of cancrinite, the short Na-H2O in the H2O-Na—H2O chain expands to form equal distances to the two H2O molecules in the chain. This causes the Na atoms to move towards the plane of the six-membered rings and forces the tetrahedra to rotate and the rings become more planar. The Na atoms then form bonds to all six (O1 and O2) oxygen atoms in a ring; the Na-O1 bonds become shorter and the Na-O2 bonds become longer. These effects cause an increase in both a and c, and thus an increase in the c/a ratio. A similar thermal expansion mechanism operates in the sodalite-group minerals where the six-membered rings and Na-Cl bond are involved.
Experimental simulation of the formation of fibrous veins by localised dissolution-precipitation creep
Authors: Bons Paul D. , Jessell Mark W. 
Published: December 2006

AbstractFibrous veins are generally interpreted in terms of the crack-seal mechanism. Several aspects of fibrous veins (fibrous structure, curved fibres, symmetry of antitaxial veins) are however better explained by vein formation without fracturing. Mass transfer to such veins would be by diffusional transport rather than by fluid flow through the veins. Deformation by dissolution-precipitation creep can provide the driving force for the necessary mass transfer. Veins form when mass transfer is heterogeneous and precipitation is localised.Experiments were performed which enforced a chemical potential gradient, acting as the driving force for diffusional mass transfer. These experiments resulted in fibrous growths in aggregates of soluble salts (NaCl and KCl) saturated with brine. The experimental results support the theory that fibrous veins may form without fracturing and that rather than providing evidence for major fluid pathways, fibrous veins may instead represent localised precipitation during diffusional material transfer.
The crystal chemistry of the solid solution series between chalcostibite (CuSbS2) and emplectite (CuBiS2)
Authors: Razmara M. F. , Henderson C. M. B. , Pattrick R. A. D. , Bell A. M. T. , Charnock J. M. 
Published: December 2006

AbstractSulphosalts in the system CuSbS2-CuBiS2(chalcostibite-emplectite) form a complete solid solution series. Seven compositions with the general formula Cu(SbxBi1–x)S2have been synthesized using dry methods at 310°C. All members of the series are orthorhombic (space groupPnma) and show smoothly increasingaandbcell parameters with substitution of Bi for Sb; theccell parameter increases up to 50% CuBiS2substitution and then becomes constant. DSC experiments on CuBiS2show an endothermic heat effect (2.45 kJ/mol.) at 472°C due to the breakdown reaction to Cu3BiS3(wittichenite) plus Bi2S3(bismuthinite). With the addition of 10% CuSbS2to CuBiS2, the decomposition temperature increases and the endothermic peak is broadened but the energy remains essentially the same (2.53 kJ/mol.). No evidence of this decomposition was observed when the amount of the CuSbS2component was >30%. The local structure and co-ordination of Cu in the samples were studied by EXAFS analysis of the Cu-Kedge but no significant variation occurs in the local Cu environment. The Debye-Waller factor for the first shell of S atoms surrounding Cu in end member CuSbS2tends to be slightly smaller than for the intermediate solid solutions, suggesting that the tetrahedral Cu environments in the intermediate composition samples is somewhat more disordered than in the end-member. The low expansion characteristics alongcappear to be controlled by the linkages between the (CuS3+ BiS2) sheets perpendicular tocbeing relatively inflexible.
Post-magmatic alteration in eudialyte from the North Qôroq centre, South Greenland
Authors: Coulson Ian M. 
Published: December 2006

AbstractThe North Qôroq centre comprises a series of nested nepheline syenite intrusions and forms part of the mid-late Proterozoic Gardar province of South Greenland. Within the centre fractionation has produced varied rock types ranging from augite-syenite to lujavrite, a eudialyte microsyenite. Samples of eudialyte from the lujavrites of unit SN1B of the centre show evidence for two-stage alteration. This alteration ranges from slight modification along crystal margins to complete breakdown and replacement by new pseudomorphing phases. Modification to crystal margins is accompanied by increasing Nb and Zr contents and is related to metasomatism produced by the intrusion of younger syenite units of the North Qôroq centre. More extensive alteration is as a result of metasomatism followed by lower-temperature supergene alteration. Simplified reactions for this breakdown include eudialyte + metasomatic fluid = allanite + nepheline; eudialyte + metasomatic fluid = titanite + aegirine + møsandrite + wöhlerite; eudialyte + fluid = zirfesite + fluid. Mass balance calculations for altered compared with unaltered samples of lujavrite show that alteration took place at approximately constant volume with an overall increase in Fe (+2.41 g/100g), Si and K (+0.65 and +0.61 g/100g), whilst Na (−2.67 g/100g) and all trace elements, particularly La, Y, Nb and Zr (−5.6 to −166 g/10000g) are lost from the system.
The crystal structure of kintoreite, PbFe3(PO4)2(OH,H2O)6
Authors: Kharisu  , Taylor M. R. , Bevan D. J. M. , Pring A. 
Published: December 2006

AbstractThe crystal structure of kintoreite, PbFe3(PO4)2(OH,H2O)6, has been refined. The mineral is rhombohedral, Rm with a = 7.3310(7), c = 16.885(2) Å, Z = 3; the structure has been refined to R = 3.0% and Rw = 3.0% using 183 observed reflections [I > 2σ(I)]. Kintoreite has the alunite-type structure which consists of sheets of corner-sharing Fe(O,OH)6 octahedra parallel to (001). The sheets are composed of clusters of three corner-linked octahedra which are tilted so that the three apical O atoms form the base of the XO4 tetrahedra. The clusters of octahedra are linked to similar groups by corner-sharing to form six membered rings. The Pb cations occupy the cavities between pairs of octahedral sheets and are surrounded by six oxygen atoms from the tetrahedra and six oxygen atoms from the octahedra to form a very distorted icosahedron. The mean bond lengths for the various coordination polyhedra are X–O 1.55 Å, (X= P, As, S); Fe–(O, OH) 2.01 Å; Pb–O 2.84 Å. The composition of the crystal used in the refinement was PbFe3(PO4)1.3(AsO4)0.4(SO4)0.3(OH,H2O)6. The XO4 anions are disordered, as in beudantite, rather than being ordered, as they are claimed to be in corkite.
Juabite, Cu5(Te6+O4)2(As5+O4)2.3H2O. a new mineral species from the Centennial Eureka mine, Juab County, Utah
Authors: Roberts Andrew C. , Gault Robert A. , Jensen Martin C. , Criddle Alan J. , Moffatx Elizabeth A. 
Published: December 2006

AbstractJuabite, ideally Cu5(Te6+O4)2(As5+O4)2·3H2O, is triclinic, space-group choices P1(1) or P(2), with unit-cell parameters refined from powder data: a = 8.984(5), b = 10.079(7), c = 8.975(5) Å, α = 102.68(7)°, β = 92.45(6)°, γ = 70.45(5)° V = 746.8(8) Å3, a:b:c = 0.8914:1:0.8905, Z = 2. The strongest seven reflections of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 9.28 (70)(010), 4.65 (70)(020), 3.097 (100)(030,11), 3.018 (60)(212), 2.658 (50)(01), 2.468 (50)(2) and 1.740 (50)(1, 521, 5). The mineral is an extremely rare constituent on the dumps of the Centennial Eureka mine, Juab County, Utah, U.S.A., where it occurs as crystalline platy masses that average 0.2–0.3 mm in longest dimension within small interconnected vugs of drusy quartz. Associated minerals are enargite, beudantite, and an undefined, possible Pb-analogue of arsenobismite. Individual crystals are subhedral to euhedral and average 125 × 100 × 1–2 µm in size. Cleavage {010} perfect. Forms are: {010} major; {100}, {01}, and {101} minor. The mineral is translucent (masses) to transparent (crystals), emerald-green, with a pale green streak, and an uneven to subconchoidal fracture. Juabite is vitreous to adamantine (almost gemmy) on cleavage faces, brittle, and nonfluorescent; H (Mohs) 3–4; D (calc.) 4.59 g/cm3 for the idealised formula. In polished section, juabite is white in plane-polarised reflected light in air with ubiquitous turquoise-blue internal reflections; bireflectance and anisotropy are unknown (due to interference from internal reflections). Averaged electronmicroprobe analyses yielded CuO 38.25, PbO 0.57, TeO3 32.58, As2O5 22.81, H2O (calc. assuming 3H2O) [5.19], total [99.40] wt.%, leading to the empirical formula (Cu5.01Pb0.03)Σ5.04(TeO4)l.93(AsO4)2.07·3.00H2O based on O = 19. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centred at 3283 cm−1 and a H-O-H flexing frequency centred at 1642 cm−1. The mineral name is for the county within the state of Utah in which the Centennial Eureka mine is located.
Mineralogy and mineral chemistry of oxide-facies manganese ores of the Postmasburg manganese field, South Africa
Authors: Gutzmer J. , Beukes N. J. 
Published: December 2006

AbstractThe diagenetic to very low-grade metamorphic manganese ores of the Postmasburg manganese field provide a unique example of oxide-facies manganese ores in a Palaeoproterozoic palaeokarst setting. The ores are composed mainly of braunite group minerals, including braunite, partridgeite and bixbyite, with rare braunite II and Ca-poor, silica-depleted braunite. Iron-poor partridgeite is distinguished from Fe-rich bixbyite and the occurrence of Ca-poor, silica-depleted braunite is reported for the first time. Braunite and partridgeite formed during early diagenesis but remained stable under greenschist facies metamorphic conditions. In contrast, bixbyite is apparently a product of metasomatic remobilisation under peak metamorphic conditions. It is suggested that local variations of the metamorphic mineral association reflect variations of the host rock composition and that they are not related to changing P-T conditions of metamorphic alteration, a model promoted by previous authors. The phase chemistry of braunite, braunite II and bixbyite is explained by the existing polysomatic stacking model for the braunite group. However, the chemical composition of partridgeite and Ca-poor, silica-depleted braunite can only be explained by introducing a distinct module layer, with partridgeite composition, to the existing polysomatic stacking model.
Bismuth and bismuth–antimony sulphosalts from Neogene vein mineralisation, Baia Borşa area, Maramureş, Romania
Authors: Cook Nigel J. 
Published: December 2006

AbstractSeveral complex Cu-Pb-Bi, Cu-Pb-Bi-Sb and Ag-Pb-Bi sulphosalt minerals have been identified in samples from hydrothermal vein mineralisation associated with the Toroiaga sub-volcanic body in the Baia Borşa area of Maramureş County, northwest Romania. This is the first chemically-documented report of Bi-sulphosalts in the Neogene metallogenic province around Baia Mare. The investigated samples contain abundant amounts of matildite solid solution within galena, the Cu-Pb/Bi sulphosalts aikinite, friedrichite, krupkaite, hammarite, lindströmite and gladite as well as nuffieldite and berryite. Within the Ag-Pb/Bi group, the majority of analysed grains can be regarded as members of the lillianite homologous series. Three distinct lillianite homologues were identified, which correspond to (i) phases along the lillianite-gustavite solid solution join (Pb3Bi2S6-AgPbBi3S6), (ii) phases within solid solution field of heyrovskyite, and (iii) compositions which best correspond to ‘schirmerite’,sensuMakovicky and Karup-Møller (1977b), but may represent disordered gustavite, vikingite or eskimoite. Some of the analysed lillianite homologues contain excess Cu, which may occupy interstitial sites. Furthermore, a large proportion of the lillianite homologues display significant substitution of Sb for Bi within the limits predicted by experimental investigations. Cosalite, also showing a range of compositions including Sb-rich varieties is recognised. Izoklakeite, Cu2Pb22(Sb,Bi)22S57, is an abundant phase throughout the analysed samples, its composition is in good agreement with previously published analyses, except for excess Cu and Fe beyond the limits previously reported. The description of several minerals from this new occurrence and compositional data on them, including the Sb-bearing varieties, provides valuable additional information on compositional limits in natural samples.