bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Relative 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

Enrichments 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.
Mineralogical nomenclature: pseudorutile revalidated and neotype given
Authors: Grey Ian E. , Watts John A. , Bayliss Peter
Published: December 2006

Pseudorutile, , has recently been revalidated as a mineral species, and the neotype locality is now South Neptune Island, South Australia. Powder X-ray diffraction data are given on a hexagonal primitive unit cell with a = 2.8667(5) and c = 4.5985(9) Å. Leucoxene, arizonite and proarizonite are considered to be mixtures. Kleberite is considered to be a hydroxylian pseudorutile, .
Zr-rich non metamict perrierite-(Ce) from holocrystalline ejecta in the Sabatini volcanic complex (Latium, Italy)
Authors: Parodi G. C. , Della Ventura G. , Mottana A. , Raudsepp M.
Published: December 2006

This paper reports the first in-situ finding of perrierite-(Ce) in Latium. The mineral occurs as brownish-red, transparent, well-developed, euhedral, prismatic crystals inside the miarolitic cavities of a holocrystalline ejectum from La Mola, Monti dell'Anguillara district, Sabatini volcanic complex.

The cell parameters (from Gandolfi film) are (in Å): a = 13.629(9), b = 5.727(1), c = 11.715(6), β(°) = 113.74(2), V(Å3) = 835.5(9). The crystal-chemical formula, based on microprobe analysis of one grain, is:

This perrierite is the most Zr-rich described so far. The entry of Zr in the C site of the structure is related to the substitution of large amounts of Ca in the A site, according to the charge balancing relationship:

The genesis of perrierite-(Ce) from La Mola is linked to late pneumatolitic-pegmatitic hypabyssal stages of the regional volcanic activity.
Schwertmannite, a new iron oxyhydroxysulphate from Pyhäsalmi, Finland, and other localities
Authors: Bigham J. M. , Carlson L. , Murad E.
Published: December 2006

Schwertmannite is a new oxyhydroxysulphate of iron from the Pyhäisalmi sulphide mine, Province of Oulu, Finland. It occurs there, and elsewhere, as an ochreous precipitate from acid, sulphate-rich waters. Associated minerals at other localities may include jarosite, natrojarosite, goethite and ferrihydrite. Schwertmannite is a poorly crystalline, yellowish brown mineral with a fibrous morphology under the electron microscope. A high specific surface area in the range of 100 to 200 m2/g, rapid dissolution in cold, 5 M HCl or in ammonium oxalate at pH 3, and pronounced X-ray diffraction line broadening are consistent with its poorly crystalline character.

Colour parameters for the type specimen as related to CIE illuminant C are L* = 53.85, a* = + 15.93, and b* = +47.96. Chemical analysis gives Fe2O3, 62.6; SO3, 12.7; CO2, 1.5; H2O−, 10.2; H2O+, 12.9; total 99.9 wt.%. These data yield an empirical unit cell formula of Fe16O16(OH)9.6(SO4)3.2·10H2O after exclusion of CO2 and H2O−. The most general simplified formula is Fe16O16(OH)y(SO4)z·nH2O, where 16 − y = 2z and 2.0 ⩽ z ⩽ 3.5. Schwertmannite has a structure akin to that of akaganéite (nominally β-FeOOH) with a doubled c dimension. Its X-ray powder diffraction pattern consists of eight broad peaks [dobs in (Iobs) (hkl)] 4.86(37)(200,111); 3.39(46)(310); 2.55(100)(212); 2.28(23)(302); 1.95(12)(412); 1.66(21)(522); 1.51(24)(004); and 1.46(18)(204,542), giving a = 10.66(4), c = 6.04(1) Å, and V = 686(6) Å3 for a primitive, tetragonal unit cell. The probable space group is P4/m. Upon heating, schwertmannite transforms to hematite with Fe2(SO4)3 occurring as an intermediate phase. Bidentate bridging complexes between Fe and SO4 are apparent in infrared spectra. Mössbauer data show the Fe in schwertmannite to be exclusively trivalent and in octahedral coordination; it has a Néel temperature of 75 ± 5 K and a saturation magnetic hyperfine field of about 45.6 T. Pronounced asymmetry of the Mössbauer spectra indicates different locations for Fe atoms relative to SO4 groups in the structure. The name is for Udo Schwertmann, professor of soil science at the Technical University of Munich.
Mikasaite, (Fe3+, Al)2(SO4)3, a new ferric sulphate mineral from Mikasa city, Hokkaido, Japan
Authors: Miura Hiroyuki , Niida Kiyoaki , Hirama Tadao
Published: December 2006

The new ferric sulphate mineral, mikasaite, the Fe analogue of millosevichite was found in Ikushunbe tsu, Mikasa city, Hokkaido, Japan. Mikasaite occurs as a sublimate around fractures from which coal gas escapes. The white-light brown coloured mineral shows aggregates of fine porous crystals. The SEM micrographs indicate that the aggregates are hollow spherical crystals of 100 µm average diameter and 1–5 µm thickness. Microprobe analysis, SO3 by wet analysis and H2O by moisture evolution analyser gives Fe2O3 24.3, Al2O3 4.3, Mn2O3 0.5, SO3 46.8, H2O(−) 23.0, total = 98.9 wt.%. The specimen adsorbed a large amount of H2O on its surface because of its strong deliquescence. As H2O is not essential to the mikasaite structure, the empirical formula on the basis of 3SO4 is (Fe1.56Al0.44Mn0.03)Σ2.03(SO4)3.00, ideally Fe2(SO4)3. The strongest 10 lines in the X-ray powder diffraction patterns, indexed on a hexagonal unit cell are (d,I/Io,hkl): 3.56, 100, 113; 5.99, 28, 012; 4.35, 23, 104; 2.97, 20, 024; 2.72, 20, 116; 2.64, 11, 211; 2.35, 7, 300; 2.24, 6, 303; 1.78, 6, 226; 3.68, 5, 006. It has space group R with hexagonal lattice parameters of a= 8.14(1) and c = 21.99(8) Å.
The roedderite-chayesite series from Spanish lamproites: crystal-chemical characterization
Authors: Alietii E. , Brigatti M. F. , Capedri S. , Poppi L.
Published: December 2006

Members of the roedderite-chayesite series in lamproites from Cancarix (SE Spain), crystallized from late magmatic residua under low PH2O, high temperature (∼ 1100°C), oxidizing conditions. They exhibit the following main chemical variations: 0.14 ⩽ Na ⩽ 0.62 atoms per formula unit (apfu); 0.80 ⩽ K⩽ 1.00 apfu; 2.97 ⩽ Mg ⩽ 4.33 apfu; 0.00 ⩽ Fe2+ ⩽ 1.19 apfu; 0.42 ⩽ Fe3+ ⩽ 0.87 apfu; they are hexagonal (10.120 ⩽ a ⩽ 10.135 Å, 14.305 ⩽ c ⩽ 14.326 Å), P6/mcc. The characteristic chemical substitution is: Fe3+ + □ ⇌ Fe2+ + (K+Na)+. Six crystal structures have been refined to 0.020 ⩽ Robs ⩽ 0.026. They have the osumilite/milarite-type structure, with Si entering the double tetrahedral T1 six-membered rings, and Mg and Fe entering both the ring-linking T2 tetrahedra, and the A octahedra. The 12-coordinated C site, located between two double rings of T1 tetrahedra, is occupied mainly by K and subordinately by Na. Furthermore, Na occupies the partially empty nine-fold coordinated B site which occurs both in the ideal (z = 0) and in a split-atom position along the c direction.
Sugilite in manganese silicate rocks from the Hoskins mine and Woods mine, New South Wales, Australia
Authors: Kawachi Y. , Ashley P. M. , Vince D. , Goodwin M.
Published: December 2006

Sugilite relatively rich in manganese has been found at two new localities, the Hoskins and Woods mines in New South Wales, Australia. The occurrences are in manganese-rich silicate rocks of middle to upper greenschist facies (Hoskins mine) and hornblende hornfels facies (Woods mine). Coexisting minerals are members of the namansilite-aegirine and pectolite-serandite series, Mn-rich alkali amphiboles, alkali feldspar, braunite, rhodonite, tephroite, albite, microcline, norrishite, witherite, manganoan calcite, quartz, and several unidentified minerals. Woods mine sugilite is colour-zoned with pale mauve cores and colourless rims, whereas Hoskins mine sugilite is only weakly colour-zoned and pink to mauve. Within single samples, the chemical compositions of sugilite from both localities show wide ranges in Al contents and less variable ranges of Fe and Mn, similar to trends in sugilite from other localities. The refractive indices and cell dimensions tend to show systematic increases progressing from Al-rich to Fe-Mn-rich. The formation of the sugilite is controlled by the high alkali (especially Li) and manganese contents of the country rock, reflected in the occurrences of coexisting high alkali- and manganese-bearing minerals, and by high fo2 conditions.
Image analysis of petrographic textures and fabrics using semivariance
Authors: Swan Andrew R. H. , Garratt Jane A.
Published: December 2006

Many subjective descriptive terms such as ‘smooth’, ‘coarse’ and ‘anisotropic’ are routinely used to convey properties of textures and fabrics, but these aspects of geological objects are not easily quantifiable. The use of directional semivariograms of image greylevels is assessed for this purpose. These quantify anisotropy of ‘coarseness/fineness’ by using semivariogram ranges, and ‘roughness/smoothness’ by using semivariogram sill values. These can be summarized by ellipses derived from semivariogram ranges and directions. The method will find applications in analysis of rock thin sections as well as analysis of surface texture of grains and microfossils.
The interpretation of granitic textures from serial thin sectioning, image analysis and three-dimensional reconstruction
Authors: Bryon D. N. , Atherton M. P. , Hunter R. H.
Published: December 2006

Textural development of the felsic phases in two granodioritic rocks from the zoned Linga superunit of the Peruvian Coastal Batholith has been characterized using serial thin sectioning, image analysis and three-dimensional reconstruction. The study has shown how each mineral phase contributed to the texture during the formation and development of a contiguous crystal framework and during subsequent restriction, isolation and occlusion of the melt-filled porosity. The work highlights the important factors and potential problems in the use of serial thin sections and imaging in the analysis of complex polyphase rock textures.
Precision serial lapping, imaging and three-dimensional reconstruction of minus-cement and post-cementation intergranular pore-systems in the Penrith Sandstone of north-western England
Authors: Cooper Mark R. , Hunter Robert H.
Published: December 2006

The application of serial lapping, imaging and image processing, and three-dimensional reconstruction techniques are discussed using the quartz-cemented Penrith Sandstone as an example. The study involves the characterization of the three-dimensional pore system microgeometry using combined back-scattered scanning electron and cathodoluminescence microscopy and focuses on the definition of post-compaction and post-cementation intergranular porosity networks. Sample preparation, section spacing and re-orientation and data presentation are described. Aspects of the application of serial section datasets and their limitations are discussed in relation to permeability studies.
A new procedure for relocating mineral grains for microprobe analysis
Authors: Potts P. J. , Tindle A. G. , Stanford D.
Published: December 2006

A new procedure is described for locating mineral grains in geological samples prepared for microprobe analysis. This procedure uses a digital image of the entire sample surface to select points of interest. These features of interest must be visible in this external image. Once the sample is mounted on the specimen stage of the microprobe, the digital image is used as a ‘map’ to relocate minerals for analysis. The image can be recorded using either a video camera, fitted with a macro zoom lens, or a flat-bed scanner. A calibration procedure has been developed in which two indexing points are used to calculate the instrument stage coordinates from the pixel coordinates of the digital image. Following this calibration, the stage coordinates of any feature visible in the digital image can be displayed to facilitate rapid relocation. The procedure was evaluated by relocating magnetite grains visible in an optical image of a geological thin section. The repositioning accuracy in relocating 28 magnetite grains distributed over an area of about 20 × 30 mm was found to be 157 ± 102 µm (one standard deviation) from the video camera image and 48 ± 28 µm from a flat bed scanner image. The former image was thought to suffer from some optical distortion. The procedure may be applied to any microprobe instrument fitted with a digital x-y specimen stage. Future applications in relocating features visible in autoradiographs are currently being evaluated.
Genesis of chemical sediments in Birimian greenstone belts: evidence from gondites and related manganese-bearing rocks from Northern Ghana
Authors: Melcher Frank
Published: December 2006

Early Proterozoic chemical sediments of the Birimian Supergroup in northern Ghana host several types of metamorphosed manganese-bearing rocks. Differences in the mineralogy and geochemistry can be attributed to facies changes in a mixed volcanic-volcaniclastic depositional environment. Manganese oxide-bearing phyllite, which is enriched in transition metals (Cu, Ni, Co, Zn), formed on the flanks of submarine volcanic edifices above an oxidation boundary. Towards the deeper basin, manganese silicate-rich gondites occur. These consist either of spessartine + quartz + ilmenite, or of spessartine + quartz + Mn amphiboles ± rhodonite ± hyalophane ± Mn stilpnomelane ± ilmenite. The Mn amphiboles are identified as manganoan actinolite, tirodite, and dannemorite. Sulphides are widespread as premetamorphic inclusions in Mn garnet grains. In the basin centre, chlorite schist containing garnet with 50–60 mol.% spessartine represents the most distal manganese-bearing rock which is highly diluted by volcanogenic background sedimentation. The origin of Mn-rich rocks is explained by heat-driven seawater convection systems active in submarine volcanic centres that provided hydrothermal solutions. Precipitation of different minerals depended on the geochemical conditions prevailing on the seafloor. During the Eburnean event (around 2000 Ma), the chemical sediments were metamorphosed to upper greenschist or lower amphibolite facies. Mineral assemblages in the gondites point to metamorphic conditions in the range of 450–500°C at 2–3 kbar.
Deposition and transport of gold by thiosulphates, Veitsch, Austria
Authors: Kucha H. , Prohaska W. , Stumpfl E. F.
Published: December 2006

Two types of gold can be distinguished in tetrahedrite from the Veitsch magnesite deposit, Austria. Primary gold present in unfractured massive tetrahedrite, has a grain size up to 18 μm and contains, on average, Cu 8.73, Ag 7.01, Au 78.63 and Hg 2.35 (wt.%). Secondary gold is present in fractures and is directly intergrown with digenite, covellite, Cu-thiosulphate, cuprite and chrysocolla but not with malachite or azurite. The secondary gold is up to 200 µm in size with an average composition of Cu 3.06, Ag 6.82, Au 86.41 and Hg 3.51 (wt.%). It is usually closely intergrown with thiosulphates containing up to 0.21 wt.% Au. This, together with the presence of ‘dirty’ gold with cloudy thiosulphate inclusions, directly indicates the transport and deposition of Au by a thiosulphate ligand. We believe this is the first reported direct evidence of gold transport and deposition by thiosulphate complexes in a natural environment.
A fusion method for preparing glass samples of peridotitic and picritic rock compositions for bulk analysis
Authors: Odling N. W. A.
Published: December 2006

A design for a micro furnace and a fusion technique are described by which silicate materials (in particular picritic and peridotitic rock compositions) may be fused and quenched to a homogeneous glass without significant loss of components, for the purposes of bulk analysis. The furnace consists of a Pt wire electrical resistance heater mounted in a furnace assembly which is fitted to a microscope stage. Microscopic examination of the sample during the fusion process allows the sample to be quenched as soon as all crystalline material has been fused and thus minimizes the loss of iron and alkalis due either to over-heating or prolonged fusion time. Analysis of glass beads of a model peridotite composition (analysed independently by X-ray fluorescence analysis) shows that for typical fusion times (5–10 seconds) the bulk composition is preserved at distances of > 25 µm from the margins of the glass beads. Analysis of natural rock powders of known composition shows that the method can be used to analyse whole rock compositions. The furnace is simple to construct and cheap to run and provides a simple and rapid method of producing glass samples for bulk analysis.
Enclaves and their bearing on the origin of the Cornubian batholith, southwest England
Authors: Stimac James A. , Clark Alan H. , Chen Yanshao , Garcia Sammy
Published: December 2006

Enclaves of diverse origin are present in minor amounts in the coarse-grained biotite granites of the Cornubian batholith, southwest England. The most common enclave type is layered, rich in biotite, cordierite and aluminosilicates, and has textures and compositions that reveal variable degrees of melt extraction from metasedimentary source rocks. Rare sillimanite-bearing enclaves represent residual material, either from the region of magma generation or its ascent path, but most such enclaves were probably derived from the contact aureole closer to the present level of exposure. These non-igneous enclaves (NIE) and their disaggregation products are present in all major plutons, comprising from < 2 to 5 vol.% of the granites. Enclaves of igneous origin are also present in all major plutons except Carnmenellis, generally comprising < 1 vol.% of the granites. The most common type is intermediate in composition, with microgranular texture, and mineral compositions and textures consistent with an origin by magma mixing. Large crystals of K-feldspar, plagioclase and quartz, common in these microgranular enclaves (ME) but absent in NIE, represent phenocrysts derived from the silicic end-member during magma mixing events rather than products of metasomatism as suggested previously. Although the composition of the mafic end-member (basaltic or lamprophyric) involved in the mixing process is poorly constrained, the presence of ME in the granites, and the preponderance of mantle-derived mafic rocks in the coeval Exeter Volcanics, indicate that mafic magma injection into the crust was a factor in the generation of the batholith. Advection of sub-crustal heat provides an explanation for large-volume crustal melting in regions of relatively thin crust such as southwest England.
Shannonite, Pb2OCO3, a new mineral from the Grand Reef Mine, Graham County, Arizona, USA
Authors: Roberts A. C. , Stirling J. A. R. , Carpenter G. J. C. , Criddle A. J. , Jones G. C. , Birkett T. C. , Birch W. D.
Published: December 2006

Shannonite, ideally Pb2OCO3, is a new mineral species that occurs as mm-sized white porcellanous crusts, associated with fluorite, at the Grand Reef mine, Graham County, Arizona, USA. Other associated minerals are plumbojarosite, hematite, Mn-oxides, muscovite-2M1, quartz, litharge, massicot, hydrocerussite, minium, and unnamed PbCO3·2PbO. Shannonite is orthorhombic, space group P21221 or P212121, with unit-cell parameters (refined from X-ray powder data): a 9.294(3), b 9.000(3), c 5.133(2) Å, V 429.3(3) Å3, a:b:c 1.0327:1:0.5703, Z = 4. The strongest five lines in the X-ray powder pattern [d in Å (I)(hkl)] are: 4.02(40)(111); 3.215(100)(211); 3.181(90)(121); 2.858(40)(130); 2.564(35)(002). The average of eight electron microprobe analyses is PbO 89.9(5), CO2 (by CHN elemental analyser) 9.70, total 99.60 wt.%. With O = 4, the empirical formula is Pb1.91C1.05O4.00. The calculated density for the empirical formula is 7.31 and for the idealized formula is 7.59 g/cm3. In reflected light, shannonite is colourless-grey to white, with ubiquitous white internal reflections (× 16 objectives), weak anisotropy, barely detectable bireflectance, and no evidence of pleochroism. The calculated refractive index (at 590 nm) is 2.09. Measured reflectance values in air and in oil (× 4 objectives) are tabulated. Transmission electron-microscopy studies reveal that individual crystallites range in size from 10–400 nm, are platy, and are anhedral. Physical properties for cryptocrystalline crusts include: white streak; waxy lustre; opaque; nonfluorescent under both long- and short-wave ultraviolet light; uneven fracture; brittle; VHN100 97 (range 93–100); calculated Mohs’ hardness 3–3½. Shannonite is soluble in concentrated HCl and in dilute HNO3 and H2SO4. The mineral name is for David M. Shannon, who helped collect the samples and who initiated this study.
Stable coexistence of grandidierite and kornerupine during medium pressure granulite facies metamorphism
Authors: Carson C. J. , Hand M. , Dirks P. H. G. M.
Published: December 2006

Petrological and mineral chemical data are presented for two new occurrences of co-existing borosilicate minerals in the Larsemann Hills, East Antarctica. The assemblages contain kornerupine and the rare borosilicate, grandidierite (Mg,Fe)A13BSiO9. Two distinct associations occur: (1) At McCarthy Point, 1–10 mm thick tourmaline-kornerupine-grandidierite layers are hosted within quartzofeldspathic gneiss; and (2) Seal Cove, where coexisting kornerupine and grandidierite occur within coarse-grained, metamorphic segregations with Mg-rich cores of cordierite-garnet-spinel-biotite-ilmenite and variably developed plagioclase halos. The segregations are hosted within biotite-bearing, plagio-feldspathic gneiss. Textural relationships from these localities indicate the stability of co-existing kornerupine and grandidierite.

The grandidierite- and kornerupine-bearing segregations from Seal Cove largely postdate structures developed during a crustal thickening event (D2) which was coeval with peak metamorphism. At McCarthy Point, grandidierite, kornerupine and late-tourmaline growth predates, or is synchronous, with F3 fold structures developed during a extensive granulite grade, normal shearing event (D3) which occurred prior to, and synchronous with, near-isothermal decompression. Average pressure calculations on assemblages that coexist with the borosilicates at Seal Cove, indicate the prevailing conditions were 5.2–5.5 kbar at ∼ 750°C for formation of the grandidierite-kornerupine assemblage.
Mineralogy of a unique graphite-containing fragment in the Krymka chondrite (LL3)
Authors: Semenenko V. P. , Girich A. L.
Published: December 2006

The Krymka chondrite contains an exotic graphite-bearing fragment that appears to be of a new type of material added to unequilibrated LL-chondrite during agglomeration on the surface of the parent body. The fine-granular texture without chondrules, two morphological groups of graphite crystals which differ in size and occurence, high content of troilite (11.3 vol.%), the high Ni (55.5–66.6 wt.%) and Co (1.59–2.87 wt.%) contents of the taenite and absence of kamacite, the presence of F-apatite, which is rare for meteorites but common for lunar and terrestrial igneous rocks, are the main features of the fragment.

The mineralogy and texture indicate: (1) the fragment probably formed by crystallization from a highly reduced silicate melt, which had been enriched in carbon; 2) the subsequent metal sulphidization lowered its abundance and resulted in the formation of troilite and the compositional features of the residual metal; (3) terrestrial weathering of an exotic fragment and the host part of the chondrite produced iron hydroxides, pentlandite and quite possibly magnetite.
Tungusite: new data, relationship with gyrolite and structural model
Authors: Ferraris Giovanni , Pavese Alessandro , Soboleva Svetlana V.
Published: December 2006

New chemical analyses, electron and X-ray powder diffraction data, and comparison with gyrolite and reyerite show that tungusite has the ideal formula , symmetry P and a = 9.714(9), b = 9.721(9), c = 22.09(3), α = 90.13(1)°, β = 98.3(2)°, γ = 120.0(1)°, Z = 1. A structural model for tungusite is derived by splitting the double tetrahedral layer of reyerite and inserting a trioctahedral X sheet which is ideally occupied by Fe2+. Polytypism phenomena due to different relative positions between tetrahedral and X sheets are discussed. A substitutional solid solution represented by the formula [Ca14(OH)8]Si24−yAlyO60[NaxM9−(x+z)□z(OH)14−(x+y+2z)·(x+y+2z)H2O] includes tungusite (x = y = z = 0, M = Fe2+ and gyrolite (x = 1, y = 1, z = 6, M = Ca).
Wupatkiite from the Cameron Uranium District, Arizona, a new member of the halotrichite group
Authors: Williams Sidney A. , Cesbron Fabien P.
Published: December 2006

Wupatkiite (Co,Mg,Ni)Al2(SO4)4.22H2O is a new member of the halotrichite group. It occurs 8 miles ESE of Gray Mountain, Arizona, near the prehistoric pueblo dwelling Wupatki. It occurs as cross-fibre veinlets with fibres up to 8mm long. Colour: empire rose (RHS48C), streak white, H. = 1 ½. G = 1.92, D(calc) = 1.87g/cm3. Nonpleochroic with α = 1.477, γ = 1.484, Z^fibre axis = 12°. Wet chemistry gave MgO 1.63, CaO 0.10, MnO 0.17, FeO 0.15, NiO 0.52, CuO 0.12, CoO 3.41, Al2O3 11.30, SO3 35.97, H2O 42.26 (total 95.63%); rem. = montmorillonite and quartz. Parameters refinedo from the powder pattern are close to those of halotrichite. Wupatkiite is monoclinic P21/c with a = 6.189 Å, b = 24.23 Å, c = 21.20 Å, β = 100.33°. Strongest lines are 4.790, 100 (024); 4.295, 27 (140); 3.945, 26 (025); 3.768, 33 (062); 3.494, 92 (124, 063).
Advances in computer modelling of mineral properties
Authors: Redfern Simon A. T.
Published: December 2006

The following six papers were presented at a meeting, held in September 1994, which reviewed some of the recent advances in the application of computational methods to mineralogy. Talks covered the developing and challenging field of ab initio quantum mechanical computations as well as new applications and insights afforded by the use and refinement of the more established methods of empirical simulation and modelling. The former attempt to solve Schrdinger's equation for the material in question, and in doing so determine the energy surface and electronic structure. The latter use parameterized interatomic potentials to describe the energy of interaction between pairs or groups of atoms, the parameters typically derived either by fitting to the results of quantum mechanical calculations of small clusters, or empirically determined from fitting to the known physical properties of crystals (e.g. to the elastic constants, structural parameters or dielectric constants). A certain rivalry and antipathy occasionally surfaces between computational theorists from either camp.
Molecular dynamics: some recent developments in classical and quantum mechanical simulation of minerals
Authors: Vočadlo Lidunka , Patel Atul , Price Geoffrey D.
Published: December 2006

We review some of the most recent developments in classical and quantum mechanical molecular dynamics simulations, in particular as applied to Earth-forming phases at conditions prevalent in the Earth's deep interior. We pay special attention to the modelling of high pressures and temperatures, elucidating the problems associated with both the classical and quantum approaches in view of the empirical potentials required for the former, and the limitations of finite temperature calculations for the latter. We show the current status of such calculations for major phases such as MgSiO3 perovskite.
Modelling the morphology of minerals by computer
Authors: Rohl A. L. , Gay D. H.
Published: December 2006

A new computer code (MARVIN) has been developed for the simulation of surfaces and interfaces. The models and methodologies employed within the program are briefly discussed. One application of the code, calculating crystal morphologies, is explored using zircon, quartz and α-Al2O3 as examples. The new code enables the use of covalent type force fields and the effect of surface relaxation on the growth morphology to be calculated for the first time. It is found that relaxation does affect the attachment energy but not by a large enough amount to significantly change the growth morphology for the three examples discussed here. Finally, the calculated surface relaxation for the basal plane of α-Al2O3 is found to be in complete agreement with Hartree-Fock ab initio calculations, verifying that the potentials, which are derived from bulk properties, transfer well to this surface.
Deriving empirical potentials for molecular ionic materials
Authors: Jackson R. A. , Meenan P. A. , Price G. D. , Roberts K. J. , Telfer G. B. , Wilde P. J.
Published: December 2006

The procedure for deriving interatomic potentials for molecular ionic materials, using empirical fitting procedures, is described. Potentials are obtained for carbonates, phosphates and perchlorates, and used to calculate crystal and lattice properties which are compared with available experimental data.
Microstructures and mineral chemistry in amphibolites from the western Tauern Window (Eastern Alps), and P-T deformation paths of the Alpine greenschist-amphibolite facies metamorphism
Authors: Schulz Bernhard , Triboulet Claude , Audren Claude
Published: December 2006

Amphibolites in the Mesozoic part of the parautochthonous Lower Schieferhülle (LSH), the allochthonous Upper Schieferhülle (USH) and the overlying Austroalpine basement (AA) in and around the western Tauern Window (Eastern Alps) suffered a progressive Alpine deformation. Lineations and foliations L1-S1, L2-S2 defined by preferentially oriented (Na-Ca) amphiboles as well as F3 folds and further foliations Smyl and S4 in the metabasites are structures of successive deformational stages with a constant W-E main extension axis of strain. The (Na-Ca) amphiboles in assemblages with epidote, chlorite, albite/oligoclase and quartz are zoned with similar continuous zonation trends from early actinolite in the cores to magnesio-hornblende and tschermakitic hornblende, and from magnesio-hornblende to late actinolite in the rims in the three lithostratigraphic units. Geothermobarometry involving tremolite-edenite and (pargasite-hastingsite)-tremolite end-member equilibria in amphiboles allowed us to reconstruct prograde-retrograde P-T paths for the Alpine greenschist-amphibolite facies event. The paths passed P/Tmax at 6–7 kbar/600°C. Similar shapes of the paths in AA, USH and Mesozoic LSH indicate a common metamorphic history and a stacking of these units prior to or during the pre-Pmax evolution. Moderate P-T ratios are characteristic for the temperature-dominated compression paths and indicate continental collisional rather than subduction zone metamorphism. The middle to late Alpine greenschist-amphibolite facies event appears as an independent metamorphism along a complete P-T loop which may have followed an earlier and poorly documented high-pressure/low-temperature event.
Megacrysts and ultramafic xenoliths from Kundelungu kimberlites (Shaba, Zaire)
Authors: Kampata M. D. , Moreau J. , Hertogen J. , Demaiffe D. , Condliffe E. , Mvuemba N. F.
Published: December 2006

Some twenty kimberlite pipes outcrop along the eastern and western borders of the Kundelungu plateau, Shaba Province, Zaire. They are arranged roughly along two north-south trending alignments. The pipes probably intruded the Bangweulu Block, which stabilized around 1800 Ma. The exceptionally fresh kimberlites contain mantle-derived nodules (peridotites and eclogites), as well as megacrysts which may reach up to several cm in diameter. The most important megacrysts are garnets, ilmenites, clinopyroxenes, orthopyroxenes and olivines. Micas and diamonds are rarely observed. The clinopyroxenes can be subdivided in two groups: (1) a Ca-rich, low-T type, similar to the Cr-rich diopsides found in ‘depleted’ (granular) peridotites; and (2) subcalcic clinopyroxene comparable to the megacrysts and to the clinopyroxenes of ‘fertile’ (sheared) peridotites. The orthopyroxenes are less frequent and are Ca-poor enstatites (0.07–0.42 wt.% CaO) and Ti-bronzites (CaO <1.3 wt.%). All the analysed garnets are Ca-rich (>4.5 wt.% CaO) and all fall in the lherzolite field defined by Sobolev et al., 1973. The low-Ca garnets which appear in many diamond-bearing kimberlites have never been observed in Zaire, neither in the diamond-poor Kundelungu pipes nor in the diamond-rich Mbuji-Mayi pipes. The ilmenites define a trend close to the ‘magmatic Mg-enrichment trend';. The olivine macrocrysts have Fo contents comparable to those of peridotites (Fo90–93). The ultramafic nodules comprise lherzolites, harzburgites, pyroxenites, wehrlites and dunites. The granular textures and P-T equilibrium conditions (770–1380°C and 28–61 kbar) deduced from their mineral compositions, show clearly that they were derived from a mantle zone on the continental geotherm (90–190 km depth). The eclogite nodules, which are less frequent, contain only two mineral phases (pyrope-almandine-grossular and omphacite), and the texture and the mineral compositions are similar to those of Roberts Victor eclogites. Our findings support the conclusion of Nixon and Condliffe (1989) that low-T peridotites, eclogites and pyroxenites derived from ‘depleted’ lithosphere, while Cr-poor garnet, subcalcic diopside and bronzite megacrysts cristallized from fertile asthenosphere.
Magnetic hausmannite from hydrothermally altered manganese ore in the Palaeoproterozoic Kalahari manganese deposit, Transvaal Supergroup, South Africa
Authors: Gutzmmer J. , Beukes N. J. , Kleyenstuber A. S. E. , Burger A. M.
Published: December 2006

Hausmannite (Mn3O4), a manganese oxide with a tetragonally distorted spinel structure, is considered to be ferrimagnetic with a very low Curie temperature of 42.5 K. However, strongly magnetic hausmannite has been discovered in some of the hydrothermally altered high-grade manganese ores of the giant Kalahari manganese deposit in South Africa. EDS-electron microprobe analyses indicate magnetic hausmannite to contain on average between 3 and 11.3 wt.% Fe2O3. In contrast non-magnetic hausmannite contains on average about 1–3 wt.% Fe2O3. X-ray powder diffraction analyses reveal small changes in cell dimensions of the magnetic hausmannite related to the high iron content. Mössbauer spectroscopy suggests that all iron is in the trivalent state. Optical microscopy and scanning electron microscopy (electron back-scatter imaging) proved the magnetic hausmannite to be homogeneous in composition, containing only a few minute inclusions of hematite. Magnetic blocking temperatures of the iron-rich hausmannite, approximating the Curie temperature, are of the order of 750 K. It is suggested that the ferrimagnetic state of hausmannite is stabilized and enhanced by replacement of Mn3+ by Fe3+.
Chlorites in a spectrum of igneous rocks: mineral chemistry and paragenesis
Authors: Abdel-Rahman Abdel-Fattah M.
Published: December 2006

The chlorite data presented are from four igneous complexes covering the compositional spectrum of igneous rocks (gabbro to granite) of orogenic and anorogenic settings. The four igneous complexes are; early orogenic gabbro-diorite-tonalite (D-T) suite, late orogenic granodiorite-adamellite (G-A) suite (both are calc-alkaline suites), high-alumina trondhjemite (TR), and anorogenic peralkaline granite (PGR).

Chlorites in these igneous rocks show characteristic compositional fields. The Mg vs Fe plot provides the best discriminant, as data points define three compositionally different groups. Phases in the PGR are Fe-rich, siliceous, interlayered chlorite-smectite (Fe/Mg = 8.6), and differ significantly from those in the calc-alkaline D-T and G-A rocks which are Mg-rich chlorites (Fe/Mg = 0.6–0.8). The X-ray diffraction data for the peralkaline granite samples show superlattice reflections at approximately 31 Å (air-dried) and 34 Å (ethylene glycollated), thus suggesting the presence of an expandable (smectite-like) component in this interlayered (chlorite-smectite) phyllosilicate phase. Chlorites in the peraluminous TR rocks contain Fe/Mg values intermediate between the other two types (Fe/Mg = 1.3). Tetrahedral Al (AlZ) values are remarkably low (0–0.5) in phyllosilicates in the PGR, but vary from 1.9–2.5 in chlorites from the other suites. Yet, these chlorite groups with their generally low AlZ values are distinct from the more stable (type IIb) metamorphic chlorites. Sedimentary chlorites are somewhat similar, in their low AlZ values and metastable structural type, to chlorites in igneous rocks.

In the calc-alkaline rocks, chlorite may have been formed at the expense of both biotite [biotite + 3M + 3H2O = chlorite + A], and calcic amphibole [2 Ca-amphibole + 6H2O + 5O2 + 1.8Al = 1 chlorite + 8SiO2 + A], where M = Fe, Mg, Al, and A = K, Na, Ca. The alteration of alkali amphibole in the peralkaline rocks may have produced interlayered chlorite-smectite via this reaction; [1 Na-amphibole + 7H2O + 2.5O2 + M = 1 chlorite-smectite + A]. The presence of such interlayered chlorite-smectite which typically form at low T (150–200°C) suggests that the region was not affected by any major reheating events, which is consistent with the nature of the feldspars.
The crystal structure and chemistry of high-aluminium phlogopite
Authors: Alietti Elisa , Brigatti Maria Franca , Poppi Luciano
Published: December 2006

Crystal structure refinements were performed on five Al-rich phlogopite-1M crystals (1.50 ⩽ Al3+ ⩽ 1.97 atoms per formula unit) from skarns of the Predazzo and Monzoni Hills petrographic area (north-east Italy) with the aim of characterizing geometrical variation produced by Al3+ increase. The charge imbalance was mostly compensated for by substitutions of highly charged cations in the octahedral sheet (Al3+ and/or Fe3+ for Mg2+). The refinements were carried out in the mean space group C2/m and gave agreement values (R) between 0.025 and 0.030. For some additional crystals, only chemistry and/or unit cell parameters were determined. In all samples the tetrahedra are more regular and larger than those previously reported in the literature for phlogopite crystals and the misfit between tetrahedral and octahedral sheets, produced by the increase in the tetrahedral edges, is mostly compensated for by the tetrahedral ring angle rotation α (10.2 °⩽ α ⩽ 12.5°), whereas the octahedral sheet features seem affected only by local crystal-chemical variations.
Crystallization from stratified magmas in the Honningsvåg Intrusive Suite, northern norway: a reappraisal
Authors: Tegner Christian , Robins Brian , Sørensen Henning S.
Published: December 2006

Wedge-shaped layers of ultramafic and mafic cumulates in Intrusion II of the Caledonian Honningsvåg Intrusive Suite suggest crystallization on an inclined magma chamber floor from a compositionally-zoned and density-stratified magma.

Cyclic unit 8 (140–100 m thick) consists of a distally-thinning olivine gabbro (denoted paoC) macrolayer overlain by a distally-thickening gabbronorite, pahC. New mineral data in four traverses across cyclic unit 8 show systematic compositional changes; the Mg# of the mafic phases decreases upwards through the unit and distally, both along the base and along the paoC/pahC interface.

A crystallization model based on an effectively continuously-zoned magma chamber with numerous, relatively thin, double-diffusive magma layers is proposed. Differential migration of horizontal isopleths (e.g. Mg# and aSiO2) in response to fractional crystallization and assimilation of country rock can explain the variations in the Mg# of the cumulates.
Compositional convection caused by olivine crystallization in a synthetic basalt melt
Authors: Seedhouse Jon K. , Donaldson Colin H.
Published: December 2006

Compositional convection in magma chambers is thought to be an important process in the fractionation of liquid from crystals during the differentiation of magmas. It has been tested for in this study by undertaking isothermal crystal growth experiments in a silicate melt at atmospheric pressure in air. The melt used is a synthetic basalt in which iron is replaced by cobalt to minimise redox problems. Co-Mg olivine rims were overgrown on forsteritic olivine seeds cemented to the floor of a 2.4 cm deep alumina crucible. Following quenching and sectioning, glasses were examined optically for colour variations and by EPMA for compositional variations. It had been expected that the colour intensity of the blue glass would diminish in the Co-depleted zone that develops around crystal overgrowths, whereas in fact little difference is normally found, except for a slight fading of colour in glass above the apex of a seed in a few experiments. By contrast EPMA revealed zones up to 50 μm wide around seeds that are depleted in Co and Mg by up to 25 % at the crystal-glass interface and in patches above some crystals. Contour maps of X-ray count-rate data obtained in grids of analytical points show Co- and Mg-depleted glass around the overgrowths and in patches above the highest point of each seed, demonstrating that convection in the melt does occur during growth of individual crystals. As the experiments were carried out in a stable temperature gradient and the crystal seeds had no contact with the melt meniscus, thermal and surface-tensional convection are both eliminated, and the convection is inferred to be caused by a density difference resulting from compositional variation across the chemical boundary layer around a growing crystal. The density difference between the inside and outside of a boundary layer is calculated to be approximately −1%.
Re-evaluation of magma compositions and processes in the uppermost Critical Zone of the Bushveld Complex
Authors: Grant Cawthorn R.
Published: December 2006

A detailed geochemical study is presented of the uppermost Critical Zone, especially of the footwall and hanging wall to the Merensky Reef, at Impala Platinum Mines in the Bushveld Complex. The approximately 100 m-thick sequence below the Merensky Reef consists of 13 distinct layers which have sharp boundaries. They are adcumulates with varying proportions of cumulus plagioclase, orthopyroxene and chromite.

Experimental studies on the composition of coexisting orthopyroxene liquid indicate that the magma which produced this sequence contained between 4 and 6% MgO. The magma from which the Merensky Reef formed was more evolved than the footwall magma.

Significant variations exist for both the En content of orthopyroxene and mg# number of whole-rock analyses in short vertical sections. Pyroxenite and norite always have higher values than anorthosite. Extremely sharp breaks in these values correlate with changes in modal proportions, and argue against both significant fractionation within the studied interval, and infiltration metasomatism. Quantitative modelling shows that the entire footwall section could have contained pyroxene with a uniform primary composition of En82, and that all the variation now observed reflects the effect of reaction with trapped magma.

Two independent methods for determining the proportion of trapped liquid are presented, based on mg# number and incompatible element abundances. Both yield a uniform proportion in all samples of approximately 10%. Immiscible sulphide liquid from the Merensky Reef can be shown to have infiltrated downwards for <5 m, despite its high density contrast with silicate magma, very low viscosity and low crystallization temperature. Residual silicate magma would have had even more restricted mobility. The migration of residual liquid or fluid through pothole structures in the floor of the Merensky Reef is not supported by the present data.