bluuebunny/crossref_metadata_2025_split huggingface dataset:
Triple-chain pyriboles in Lewisian ultramafic rocks
Authors: Droop G. T. R. 
Published: December 2006

AbstractThe triple-chain pyriboles jimthompsonite, clinojimthompsonite, and probably chesterite and its monoclinic polytype occur in Lewisian amphibolite-facies ultramafic rocks near Achmelvich, N.W. Scotland. These minerals are intergrown with one another and with amphiboles in prismatic porphyroblasts up to 3 cm long, which are associated with chlorite, carbonate, magnetite and, in some cases, talc. Rocks containing triple-chain silicates have been found at three localities, in each case outcropping in a layer < 1.5 m thick. Clinojimthompsonite is the most abundant triple-chain silicate and generally forms euhedral wedge-shaped overgrowths, measuring up to 1 mm in the b-axis direction, on the {010} faces of actinolite cores. The mineral assemblages are probably of Inverian age.The identification of the triple-chain phases is based mainly on cleavage angle, extinction angle, backscattered electron intensity and, in the case of clinojimthompsonite, on X-ray diffraction data. Microprobe analyses support the identifications. The triple-chain silicates have compositions lying in the system MgO-FeO-SiO2-H2O, with only trace amounts of other components.The cell dimensions of the coarsest clinojimthompsonite are: a = 9.862 ± 0.002 Å, b = 27.184 ± 0.020 Å, c = 5.298 ± 0.004 Å, β = 109.61° ± 0.14° V = 1337.9 ± 1.8 Å3, and its optical properties are as follows: α = 1.600 β = 1.619 γ = 1.628 (all ± 0.001) and optic axial plane = (010). The 2Vα of clinojimthompsonite = 67 ±2°.Back-scattered electron microscopy reveals that although substantial volumes of single-phase clinojimthompsonite are common, (010) intergrowths of Mg,Fe-amphiboles, jimthompsonite polytypes and chesterite polytypes occur locally on scales down to 0.1 µm and probably smaller, indicating considerable chain-width disorder.The triple-chain pyriboles are not pseudomorphous after amphibole and probably grew during prograde Inverian metamorphism. Chemographic constraints suggest that they could have formed from forsterite-bearing assemblages, possibly as the result of infiltration of CO2-rich fluid. Thermodynamic calculations for associated high-variance ultramafic rocks place an upper limit of c. 600–700°C on the temperature of metamorphism.The large number of chemically similar pyriboles and their disposition within compound prisms suggests that crystallization was kinetically controlled. A simple ‘template’ model is propesed to explain the observed patterns, in which the identity of the Mg,Fe-pyribole nucleating at any point on a preexisting actinolite or Mg,Fe-pyribole substrate is controlled by silicate-chain width and/or symmetry (ortho vs. clino), depending on the orientation of the substrate crystal face.
Bismuth sulphosalts within quartz veining hosted by the Loch Shin monzogranite, Scotland
Authors: Lowry D. , Stephens W. E. , Herd D. A. , Stanley C. J. 
Published: December 2006

AbstractThe Loch Shin monzogranite is host to quartz veins bearing the sulphosalts aikinite, hammarite, lindströmite, krupkaite, gladite and pekoite, which belong to the aikinite-bismuthinite series, and represents the first significant occurrence of this series in the United Kingdom. Inclusions of the sulphotelluride tetradymite occur in krupkaite-gladite. Berryite is present as inclusions in chalcopyrite. Electron microprobe analyses reveal a range of compositions in individual crystal masses from hammarite to krupkaite in one sample, and from krupkaite to gladite in a second. Compositions between friedrichite and hammarite and gladite and pekoite are notably absent.
Parkinsonite, (Pb,Mo, □)8O8Cl2, a new mineral from Merehead Quarry, Somerset
Authors: Symes R. F. , Cressey G. , Griddle A. J. , Stanley C. J. , Francis J. G. , Jones G. C. 
Published: December 2006

AbstractParkinsonite, ideally (Pb,Mo,□)8O8Cl2, is a new mineral from the Merehead Quarry, Cranmore, Somerset, England. It occurs as compact clusters or patches of red to purplish red bladed crystals, which have an adamantine lustre and a perfect {001} cleavage and occupy fractures and cavities in carbonate vughs in veins of manganese and iron oxide and hydroxide minerals. Associated minerals are mendipite, diaboleite, chloroxiphite, wulfenite, cerussite and hydrocerussite. Discrete crystals were not found; intergrown crystalline aggregates are the usual form of occurrence. The maximum grain size is about 300 × 100 µm, but most grains are appreciably smaller. Parkinsonite was synthesized using high purity chemicals. The measured density of the synthetic material is 7.32 g/cm3; the calculated density is 7.39 g/cm3, the difference being due to minor impurity and slight porosity in the synthetic sample. Parkinsonite is translucent. Reflectance spectra were obtained in air and in oil. Refractive indices calculated from these (at 589 nm) are for Ro, 2.58, and Re', 2.42, i.e. uniaxial negative. VHN50 is 113–133 from which the calculated Mobs hardness is 2–2.5.X-ray studies show that parkinsonite is tetragonal with space group I4/mmm, I4̄2m, I4̄m2, I4/mm, or I422 and a 3.9922(3), c 22.514(2) Å. It has a cell volume of 358.82(5) Å3 with Z = 1. The strongest six lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)] 2.823, 2.813(100) (110,008); 5.63(85) (004); 2.251(33) (116, 0.0.10); 2.988(27) (105); 3.750(15) (006); 1.994(11) (200,118). Averaged electron microprobe analyses give the empirical formula Pb6.34Mo0.89□0.77O8.02Cl1.98 on the basis of 10 atoms [O + Cl]. The name is for Reginald F. D. Parkinson, mineral collector of Somerset, UK, who first found the mineral.
Fiedlerite: revised chemical formula [Pb3Cl4F(OH)·H2O], OD description and crystal structure refinement of the two MDO polytypes
Authors: Merlino S. , Pasero M. , Perchiazzi N. 
Published: December 2006

AbstractThe chemical formula of fiedlerite, a rare hydrated lead halide, has been revised. The mineral is now known to contain also fluorine, and the new, correct formula is Pb3Cl4F(OH)·H2O. X-ray diffraction studies on fiedlerite from Laurion, Greece (the type locality), and from Baratti, Italy (the second known occurrence), revealed its Order-Disorder (OD) character. All structures within this OD family can be built up by layers of the same kind. The two polytypes with Maximum Degree of Order (MDO) display triclinic and monoclinic symmetry, with one and two OD layers, respectively, in the unit cell. On these grounds the nomenclature of fiedlerite has been revised, and the mineral is designated together with the polytype suffix (i.e. fiedlerite-1A, fiedlerite-2M). The crystal structures of the two MDO polytypes of fiedlerite have been solved and refined: fiedlerite-1A:P,a= 8.574(3) Å,b= 8.045(4),c= 7.276(2), α = 89.96(4)° β = 102.05(4), γ = 103.45(4),R= 0.092; fiedlerite-2M:P21/a,a= 16.681(4) Å,b= 8.043(3),c= 7.281(2), β = 102.56(4)°,R= 0.061. In both structures Pb is eight-coordinated by different ligands [CI−, F−, (OH)−, H2O] that define bicapped trigonal prisms.
Lattice perfection and growth history of doubly-terminated natural alpha quartz crystals
Authors: Lang A. R. , Makepeace A. P. W. , Moore M. 
Published: December 2006

AbstractSynchrotron X-ray topography was the principal perfection-assessment method employed. X-ray wavelengths were chosen that gave optimum penetration and diffraction contrast characteristics for the size of crystals examined. Two colourles transparent specimens were selected for comprehensive study. Both were of simple habit consisting of the prism {101̄0} terminated at each end by major and minor rhombohedral facets only. The larger specimen, volume ≈250 mm3, contained a moderately high but non-uniformly distributed dislocation population, totalling ≈103, all emanating from a roughly centrally located small nuclear volume. One apical region was dislocation-free. Optical microscopic observations including Nomarski interference contrast of features on one major rhombohedral facet in this region are described. The smaller specimen, volume ≈30 mm3, was remarkable for its low dislocation content, ≈20 in total, all radiating from a central point. Enhancement of dislocation image visibility relative to diffraction contrast images of severe surface damage on this crystal was demonstrated using higher-order X-ray reflections. Neither of the specimens studied in detail contained twinning or evident diffraction contrast from impurity zoning. Their lack of a microscopically visible or X-ray topographically detectable nucleating body favours a homogenous nucleation origin of these crystals.
Zaoyang chondrite cooling history from Fe2+-Mg intracrystalline ordering in pyroxenes
Authors: Molin Gian Mario , Tribaudino Mario , Brizi Elisabetta 
Published: December 2006

AbstractThe crystal chemistry of clinopyroxene, orthopyroxene and olivine from a crushed fragment of the H5 Zaoyang chondrite has been investigated by X-ray structure refinement and detailed microprobe analysis. The meteoritic pyroxenes have cell and polyhedral volumes which compare well with such data from terrestrial pyroxenes that typically crystallize at low-pressure. Fe2+ and Mg are rather disordered in M1 and M2 sites of clino- and orthopyroxenes; the closure temperatures of the exchange reaction are 600 and 512°C respectively, which is consistent with a reasonably fast cooling rate, estimated to be of the order of 1°C/day.The closure temperature for the intercrystalline Ca-Mg exchange reaction for clino- and orthopyroxenes is 900°C as calculated from clino- and orthopyroxene intergrowth.The cooling rates obtained from Fe2+-Mg intracrystalline partitioning suggest a cooling of the order of degrees per day at temperatures of 600–500°C due to a strong loss of heat by irradiation.
An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution
Authors: Schofield P. F. , Charnock J. M. , Cressey G. , Henderson C. M. B. 
Published: December 2006

AbstractEXAFS spectroscopy has been used to monitor changes in divalent cation site geometries across the P2/c-P1̄ phase transition in the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution at ambient and liquid nitrogen temperatures. In the ZnWO4 end member, Zn occupies axially-compressed ZnO6 octahedra with two axial Zn-O bonds at approximately 1.95 Å and four square planar Zn-O bonds at approximately 2.11 Å. The substitution of Zn by Cu generates a second Zn environment with four short square planar Zn-O bonds and two longer axial Zn-O bonds. The proportion of the latter site increases progressively as the Cu content increases. Cu EXAFS reveals that the CuO6 octahedra maintain their Jahn-Teller axially-elongate geometry throughout the majority of the solid solution and only occur as axially-compressed octahedra well within the stability field of the Zn-rich phase with monoclinic long-range order.
Compositional variation of cooperite, braggite, and vysotskite from the Bushveld Complex
Authors: Verryn Sabine M. C. , Merkle Roland K. W. 
Published: December 2006

AbstractThe compositions of coexisting and individual cooperite (ideally PtS) and braggite (ideally (Pt,Pd)S) grains from the Merensky Reef of the Bushveld Complex, as well as cooperite, braggite and vysotskite (ideally PdS) grains from the UG-2 of the Bushveld Complex were investigated. There is a clearly defined miscibility gap between cooperite and braggite, but no evident gap between braggite and vysotskite. Partition coefficients between cooperite and braggite are determined on coexisting phases. The KDbraggite/cooperite in atomic ratios are estimated to be 0.54 for Pt, 15.81 for Pd and 5.93 for Ni. For Rh and Co the KDbraggite/cooperite are estimated to be > 1.40 and > 1.46 respectively. No systematic behaviour is detected for Fe and Cu. Coupled substitutions of Pd + Ni for Pt in cooperite and braggite/vysotskite are indicated. Within the cooperite of the Merensky Reef, the Pd:Ni ratio is approximately 9:11. The substitution trend in braggite, which extends to vysotskite in the UG-2, is dependent on the base-metal sulphide (BMS) association. If pentlandite is the dominant Ni-bearing BMS, the Pd:Ni ratio is about 7:3 in the Merensky Reef and in the UG-2. Millerite as the dominant Ni-bearing BMS in the UG-2 changes this ratio to 3:1. It is concluded that the Ni-content in braggite/vysotskite from BMS assemblages does not depend on the NiS activity, but rather on temperature of formation.
A thermodynamic prediction on the stability of the nukundamite + chalcopyrite and bornite + pyrite assemblages
Authors: Kojima Shoji , Ueno Teiichi 
Published: December 2006

AbstractA thermodynamic prediction of the Gibbs free energy of formation (ΔGfo) of nukundamite (empirical composition Cu5.5FeS6.5) was made in order to specify whether the nukundamite + chalcopyrite or the bornite + pyrite assemblage is stable in the Cu-Fe-S system. The results of calculations using previously reported data of ΔGfo values of some Cu-Fe-sulphide minerals in equilibrium with nukundamite indicate that the total free energy of the nukundamite + chalcopyrite assemblage is appreciably higher than that of the bornite + pyrite assemblage in the temperature range 250–400°C. This means that nukundamite + chalcopyrite is a metastable assemblage under common ore-forming conditions.The occurrence of nukundamite is not uncommon in the Fijian kuroko deposits in contrast to the Japanese kuroko deposits. A thermochemical treatment for this phenomenon leads to the interpretation that the black ore containing nukundamite in the Fijian deposit was formed under relatively highsulphidation and low-pH conditions. This suggestion is in good agreement with the present experimental result that the bornite + pyrite assemblage was produced in the temperature range 350–250°C by using near-neutral hydrothermal solutions.
Crystal chemistry and intracrystalline relationships of orthopyroxene in a suite of high pressure ultramafic nodules from the ‘Newer Volcanics’ of Victoria, Australia
Authors: Molin Gianmario , Stimpfl Marilena 
Published: December 2006

AbstractA suite of orthopyroxenes from spinel Iherzolite xenoliths associated with basanites occurring in the Victorian (Australia) post-Pliocene ‘Newer Volcanics’ province was investigated by means of a crystal chemical methodology which provides accurate site occupancy and site configuration parameters.The M1 configuration is essentially constrained by AlVI rather than Fe2+. In addition, Fe3+, Cr3+ and Ti4+ are confined to M1 (Molin, 1989) and AlIV to TB. M2 is controlled by FeM22+ ⇌ MgM2, constrained by (Fe2+ + Ca)M2 > 0.14 atoms per formula unit (p.f.u.). Cation substitution in TB and M2 constrains the sum of the volumes of the respective polyhedra VTB+VM2 to remain essentially constant. Therefore, M2 favours the retention of the large Fe2+ up to melting-point, causing non-ideality of this iron-depleted orthopyroxene. As a consequence, the investigated orthopyroxene can be considered an ultimate Fe2+ carrier during partial mantle melting.
Occurrence and genetic implications of hyalophane in manganese-rich iron-formation, Cuyuna Iron Range, Minnesota, USA
Authors: McSwiggen Peter L. , Morey G. B. , Cleland Jane M. 
Published: December 2006

AbstractThe recent discovery of hyalophane [(K,Ba)Al1−2Si3−2O8] on the North range segment of the Early Proterozoic Cuyuna Iron Range of east-central Minnesota has shed new light on the depositional environment of these rocks. This Ba-feldspar occurs in a 10 m thick interval within the main iron-formation and typically contains between 8 and 26 mol.% celsian (BaAl2Si2O8). Its occurrence in several textural settings suggests that barium was being deposited at various stages in the paragenetic history of the iron-formation. Some of the hyalophane grains occur as the cores of micronodules, which are structurally similar to oolites or oncolites, but mineralogically are very complex. The hyalophane also occurs as rims on core grains of diverse mineral composition and as discrete phases in late crosscutting veins.Hyalophane, like other Ba-silicates, has a very restricted paragenesis. They are associated typically either with sedimentary manganese and ferromanganese deposits, or with Cu-Pb-Zn-Ba deposits. The presence of hyalophane in the Early Proterozoic manganiferous iron ores of east-central Minnesota casts doubt on the historic interpretation of these deposits as typical Superior-type sedimentary iron-formations and instead supports the view that these deposits, at least in part, consist of chemical sediments from a hydrothermal fumarolic system. The suggested involvement of a hydrothermal system is also supported by the occurrence of aegirine within the hyalophane-rich layer, and the occurrence of tourmalinites and Sr-rich baryte veins elsewhere in the Cuyuna North range.
Mcalpineite, Cu3TeO6·H2O, a new mineral from the McAlpine mine, Tuolumne County, California, and from the Centennial Eureka mine, Juab County, Utah
Authors: Roberts Andrew C. , Scott Ercit T. , Criddle Alan J. , Jones Gary C. , Scott Williams R. , Cureton Forrest F. , Jensen Martin C. 
Published: December 2006

AbstractMcalpineite, ideally Cu3TeO6·H2O, occurs as isolated 0.5 mm-sized emerald green cryptocrystalline crusts on white quartz at the long-abandoned McAlpine mine, Tuolumne County, California, U.S.A. Associated nonmetallic phases are muscovite (mariposite), calcite, goethite, hematite, chlorargyrite, choloalite, keystoneite, mimetite, malachite, azurite, annabergite and a host of unidentified crusts, both crystalline and amorphous. Associated metallic minerals include pyrite, acanthite, hessite, electrum, altaite, native silver, galena, pyrargyrite, sphalerite and owyheeite. The mineral has also been identified at the Centennial Eureka mine, Juab County, Utah, U.S.A., where it occurs as interstitial olive-green coatings and as millimetre-sized dark green-black cryptocrystalline nodules lining drusy quartz vugs. Associated minerals are xocomecatlite, hinsdalite-svanbergite, goethite and several new species including two hydrated copper tellurates, a hydrated copper-zinc tellurate/tellurite, and a hydrated copper-zinc tellurate/tellurite-arsenate-chloride. Mcalpineite is cubic, P-lattice (space group unknown), a = 9.555(2) Å, V = 872.4(4) Å. The strongest six lines in the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 4.26(40)(210), 2.763(100)(222), 2.384(70)(400), 1.873(40)(431,510), 1.689(80)(440) and 1.440(60)(622). The average of four electron-microprobe analyses (McAlpine mine) is CuO 50.84, NiO 0.17, PbO 4.68, SiO2 0.65, TeO3 39.05, H2O (calc.) [4.51], total [100.00] wt. %. With O = 7, the empirical formula is (Cu2.79Pb0.09Ni0.01)∑2.89(Te0.97Si0.05)∑1.02O5.90·1.10H2O. This gives a calculated density of 6.65. g/cm3 for Z = 8. The average of two electron-microprobe analyses (Centennial Eureka mine) is CuO 51.2, ZnO 3.1, TeO3 39.0, SiO2 0.2, As2O5 0.8, H2O (by CHN elemental analyser) 7, total 101.3 wt. %, leading to the empirical formula (Cu2.56Zn0.15)∑2.71 (Te0.88Si0.02As0.02)∑0.92O5.47·1.53H2O. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centred at 3320 cm−1 and a H-O-H flexing frequency centred at 1600 cm−1. In reflected light Mcalpineite is isotropic, nondescript grey, with ubiquitous brilliant apple to lime green internal reflections. The refractive index calculated from Fresnel equations is 2.01. Measured reflectance values in air and in oil are tabulated. Reflectance study also shows that cryptocrystalline aggregates are composed of micron-sized sheaves of fibrous or prismatic crystals. Other physical properties include: adamantine lustre; light green streak; brittle; uneven fracture; translucent to transparent and nonfluorescent under both long- and short-wave ultraviolet light. The name is for the first known locality, the McAlpine mine.
Crystal structures of synthetic 7 Å and 10 Å manganates substituted by mono- and divalent cations
Authors: Kuma Kenshi , Usui Akira , Paplawsky William , Gedulin Benjamin , Arrhenius Gustaf 
Published: December 2006

AbstractThe crystal structures of synthetic 7 Å and 10 Å manganates, synthetic birnessite and buserite, substituted by mono- and divalent cations were investigated by X-ray and electron diffractions. The monoclinic unit cell parameters of the subcell of lithium 7 Å manganate, which is one of the best ordered manganates, were obtained by computing the X-ray powder diffraction data: a = 5.152 Å, b = 2.845 Å, c = 7.196 Å, β = 103.08°. On the basis of the indices obtained by computing the X-ray diffraction data of Li 7 Å manganate, monovalent Na, K and Cs and divalent Be, Sr and Ba 7 Å manganates were interpreted as the same monoclinic structure with β = 100–103° as that of Li 7 Å manganate, from their X-ray diffraction data. In addition, divalent Mg, Ca and Ni 10 Å manganates were also interpreted as the same monoclinic crystal system with β = 90–94° The unit cell parameters, especially a, c and β, change possibly with the type of substituent cation probably because of the different ionic radius, hydration energy and molar ratio of substituent cation to manganese. However, these diffraction data, except for those of Sr and Ba 7 Å and Ca and Ni 10 Å manganates, reveal only some parts of the host manganese structure with the edge-shared [MnO6] octahedral layer. On the other hand, one of the superlattice reflections observed in the electron diffractions was found in the X-ray diffraction lines for heavier divalent cations Sr and Ba 7 Å and Ca and Ni 10 Å manganates. The reflection presumably results from the substituent cation position in the interlayer which is associated with the vacancies in the edge-shared [MnO6] layer and indicates that the essential vacancies are linearly arranged parallel to the b-axis. Furthermore, the characteristic superlattice reflection patterns for several cations, Li, Mg, Ca, Sr, Ba and Ni, manganates were interpreted that the substituent cations are regularly distributed in the interlayer according to the exchange percentage of substituent cation to Na+. In contrast, the streaking in the a-direction observed strongly in the electron diffractions for heavier monovalent cations, K and Cs, manganates probably results from the disordering of their cations in the a-direction in the interlayer.
Use of element-mineral correlations to investigate fractionation of rare earth elements in fine-grained sediments
Authors: Temple J. T. , Walsh J. N. 
Published: December 2006

AbstractRelative concentrations of elements in the minerals of fine-grained sediments can be inferred from element-mineral correlation coefficients. The technique is applied to the distribution of REE in Middle Ordovician shales from South Wales analysed by ICPAES, Leco C/S125 and XRD. Phosphate and chlorite show mid-REE enrichment; muscovite + biotite shows mid-REE depletion. The complementarity of the chlorite and muscovite + biotite patterns may be due to fractionation during diagenetic recrystallisation. Partial correlation analysis is used to infer the presence of zircon.
Hollandite in Hawaiian basalt: a relocation site for weathering-mobilized elements
Authors: Fodor R. V. , Jacobs R. S. , Bauer G. R. 
Published: December 2006

AbstractEnrichments in Ba, REE and Y abundances, occurrences of REE, Y-bearing phosphate, depletions in K and Rb, and negative Ce anomalies in some lavas on Kahoolawe (Hawaii) reflect secondary mobilization of Ba, REE, Y, K and Rb. Hollandite (Ba-Mn-oxide) in the groundmass of a Kahoolawe lava contains nearly 10 wt.% BaO, ∼ 1.1 wt.% CeO2, and small amounts of La, Nd, Y, K, Na, P, Cl and Cu to provide an example of where elements mobilized during weathering processes on the Hawaiian Islands find residence. Fe-vernadite, a second Mn-oxide, also hosts mobilized REE and Ba. A positive Ce anomaly in the hollandite complements the negative Ce anomaly in some Kahoolawe lavas, this is analogous to Ce accumulation in todorokite of manganese nodules complementing Ce-depleted seawater. Mn-oxides, then, can serve as links between lavas depleted and enriched in certain elements.