bluuebunny/crossref_metadata_2025 huggingface dataset:
Gonnardite and disordered natrolite-group minerals: their distinction and relations with mesolite, natrolite and thomsonite
Authors: Nawaz Rab
Published: December 2006

This paper presents a literature survey of compositions of the fibrous zeolites mesolite, natrolite, thomsonite and their derivatives such as pseudomesolite, high-Na mesolite, tetranatrolite, paranatrolite, ranite, and gonnardite, and evaluates them in the light of new electron probe analyses and X-ray powder data for gonnardites and associated minerals from Aci Castello, Gignat, Hills Port, Kladno, and Lamo. The analyses are plotted on the basis of bivalent vs. trivalent cations per 80 oxygen cell and a new chemical classification is tentatively proposed. It is concluded that ranite is definitely not synonymous with gonnardite and until species status is confirmed it is useful to retain this term as a Ca- and Al-rich disordered variety of natrolite. It is further concluded that natrolite and tetranatrolite contain up to 2 Ca, ranite 2–4 Ca, gonnardite 4–6 Ca and thomsonite 6–8 Ca atoms with corresponding limits on the Al atoms. Compositions are governed by NaSi = CaAl and to some extent by Na2 = Ca type replacements and the Al-content generally varies sympathetically with Ca-content. The plot reveals that most high-Na mesolites are ranites, a number of gonnardites are ranites and one or two are tetranatrolites. The compositional field of gonnardite crosses that of mesolite (and pseudomesolite), but these minerals can be easily distinguished optically and by their powder patterns. The unit cell volumes increase in the order tetranatrolite, ranite, gonnardite and paranatrolite, therefore if the 1040 (or 1460) line can be identified in the powder patterns one can distinguish between these minerals. New infrared spectra of gonnardite, ranite and tetranatrolite are compared with each other and with published spectra, and differences are noted. DSC results for gonnardite and ranite are compared and appear to be diagnostic.
Mössbauer effect study on the mixed valence state of iron in tourmaline
Authors: Ferrow E. A. , Annersten H. , Gunawardane R. P.
Published: December 2006

Mössbauer spectra of iron-bearing tourmaline, obtained at different temperatures, show the existence of thermally-activated charge delocalization among clusters of iron atoms situated in the Y and Z octahedra of the tourmaline structure. The temperature dependence indicates an unusually high activation energy for the delocalization process which suggests that the process takes place between crystallographically non-equivalent sites. Annealing of the tourmaline in hydrogen is observed to inhibit the delocalization process, thus localizing the electron into the Z-site.
Intracellular aragonite crystals in the flesh-water alga,Spirogyrasp.
Authors: Mann S. , Mann H. , Fyfe W. S.
Published: December 2006

Intracellular crystals of aragonite have been identified by selected area electron diffraction (SAED) in the freshwater filamentous algaSpirogyrasp. which grows sporadically as carpets in the Thames river, Ontario, Canada. The crystals are 2 to 24 µm in length, and characterized by a unique cross-shaped morphology, in which needle-like, or prismatic outgrowths develop from a common axis. Crystals may be dispersed through filaments, but tend to cluster as aggregates towards the centre.
Silicate Mineralogy of the Middle Zone Cumulates and Associated Gabbroic Rocks from the Insch Intrusion, NE Scotland
Authors: Wadsworth W. J.
Published: December 2006

The Middle Zone (MZ) of the Insch intrusion lies in a geographically intermediate position between the Lower Zone (LZ) and Upper Zone (UZ) cumulate sequences, but is more complicated than either in comprising two intricately associated, but texturally distinct, components, the MZ cumulates and the fine-grained granular gabbros (FGG). In addition, there is a minor group of porphyritic granular gabbros (PGG), containing abundant plagioclase phenocrysts. A further variety of gabbroic rock, namely quartz-biotite norite (QBN) occupies a similarly intermediate position in the Boganclogh extension of the main Insch mass. These principal components (MZ cumulates, FGG, and QBN) show considerable mineralogical overlap with each other and with the lower part of the UZ succession (UZa). Unlike the UZ rocks, they are essentially olivine-free (apart from the most basic granular gabbros) and consist mainly of plagioclase, orthopyroxene, and Ca-rich clinopyroxene, with accessory Fe-Tioxides and minor interstitial biotite and/or hornblende. Mineral compositions are in the range An70–55 (plagioclase), En71–44 (opx), and Ca46Mg42Fe12 to Ca45Mg30Fe25 (cpx), but in detail each rock group can be characterized mineralogically as well as texturally. It is concluded that the MZ cumulates and FGG (including PGG) are essentially complementary, formed in different locations, and under slightly different conditions, but in the same magma chamber. The complex relationships between them, and the apparently haphazard geographical variations in mineral compositions, may be the combined results of the magmatic events, possibly including the movement of large xenolithic fragments, and later block faulting. The substantial compositional overlap of the more evolved MZ cumulates by UZa is explained in terms of replenishment by magma of slightly more primitive (and potentially olivine-bearing) composition after the deposition of the MZ. The Boganclogh QBN is believed to represent a more hydrous fraction of the Insch MZ magma.
Roxbyite, a New Copper Sulphide Mineral from the Olympic Dam Deposit, Roxby Downs, South Australia
Authors: Mumme W. G. , Sparrow G. J. , Walker G. S.
Published: December 2006

Roxbyite (Cu1.74–1.82S), a new mineral, was isolated from drill core from the Olympic Dam deposit, from copper flotation concentrates from the Olympic Dam pilot plant, and from reaction residues obtained by treating certain concentrates with sulphuric acid. Powder X-ray diffraction data and the composition of the mineral are similar to results reported previously for the unnamed mineral of composition Cu1.83S (with a trace of iron) from the El Teniente deposit in Chile, and to copper sulphides of composition CuxS, 1.75 ⩽x⩽ 1.86, prepared electrochemically by several workers. A Weissenberg single-crystal study shows roxbyite to be monoclinic witha= 53.79,b= 30.90,c= 13.36Å, β = 90.0° and space group alternatives C2/m, Cmor C2. Some iron in the structure may stabilize the mineral.
Vanadium-Bearing Margarite from the Lachlan Fold Belt, New South Wales, Australia
Authors: Morand V. J.
Published: December 2006

Margarite occurs in Ordovician black slate within the contact aureole of the Wyangala Batholith, in the Lachlan Fold Belt in New South Wales. This occurrence is the first described from New South Wales. It is a regional metamorphic mineral replacing chiastolitic andalusite, and contains up to 1.07% V2O3 and up to 0.37% Cr2O3. Vanadium and chromium here substitute for octahedral aluminium. Margarite is produced by a local reaction in which Ca and H2O are introduced into andalusite grains. There is a significant paragonite component in the margarite but negligible muscovite solid solution.
Chemical Composition of Fluorapatite and Associated Minerals from Skarn Near Gatineau, Quebec
Authors: Hogarth D. D.
Published: December 2006

Sixteen fluorapatite specimens from regional skarns in granulite terrain were associated with Al-zoned diopside ± scapolite ± actinolite ± calcite(+ rare phlogopite). Apatite was low in Ce (ave. 0.19% Ce2O3) and enriched in LREE relative to HREE (La/Yb = 31 to 74 in 4 specimens). Some specimens showed small negative Eu anomalies and some crystals were zoned in REE. SrO averaged 0.36%. The mineral contained some carbonate (ave. 0.5% CO2 in 5 specimens), appreciable silica (ave. 0.5%), and variable sulphate (0.1 to 1.2% SO3). Excess charge due to S6+ was largely compensated by Si4+. Chlorine was minor and F accounted for 75–98% of the F, Cl and OH ions. Apatite from marble lacking amphiboles and pyroxenes has a similar chemical composition, but apatite from later carbonatite and fenite contains more Ce and Sr. Apatite from Gatineau fenite, Gatineau carbonatite and world-wide siliceous igneous rock generally contains less S. Apatite from Gatineau skarns normally contains more Cl and less S than that from phosphorite. Magnesian marble was silicated to skarn by reaction with siliceous gneiss. Phosphorus, REE, and Sr were removed from nearby rocks and transported in aqueous, carbonated solutions containing minor amounts of F, Cl and S at granulite-facies conditions. Apatite and calcite precipitation took place in skarns and marble during the Grenville (Proterozoic) orogeny.
Kaersutite-Bearing Xenoliths and Megacrysts in Volcanic Rocks from the Funk Seamount in the Southwest Indian Ocean
Authors: Reid Arch M. , le Roex Anton P.
Published: December 2006

Eight samples (seven volcanic rocks and one quartz sandstone) have been dredged from the Funk Seamount, 60 km NW of Marion Island in the southwest Indian Ocean (lat. 46° 15′S, long. 37° 20′ E). The volcanic rocks are fine-grained vesicular basanitoids and glass-rich volcanic breccias geochemically similar to the Marion Island lavas. Lavas and breccias contain a suite of megacryst minerals and of small polymineralic xenoliths, in both of which kaersutite is a prominent constituent.

The megacryst suite comprises large unzoned single grains of kaersutite, plagioclase, pyroxene, magnetite and ilmenite, all showing textural evidence of resorption/reaction with the basanitoid host. The megacrysts have a limited range of compositions except for the plagioclase which ranges from oligoclase to labradorite.

The small (2 mm to ∼ 3 cm) xenoliths are mostly two-pyroxene amphibole assemblages with or without olivine, magnetite, ilmenite, plagioclase and apatite. The xenoliths show some evidence of reaction with the basanitoid host and most have undergone recrystallization and/or localised decompression melting.

Xenolith and megacryst assemblages are interpreted as being associated with the formation and partial crystallization of a hydrous basanitoid melt at depth.
A Nitrogen-Rich Metamorphic Fluid and Coexisting Minerals in Slates from North Wales
Authors: Bottrell S. H. , Carr L. P. , Dubessy J.
Published: December 2006

Volatile species analysis of fluid inclusions in metamorphic quartz veins from the Llanbedr Formation, North Wales, show nitrogen to be an important component. Microthermometric and Laser Raman analysis indicates that the N2 is resident in a generation of very N2-rich inclusions and demonstrates the presence of both N2-rich and aqueous fluids during metamorphism of the Llanbedr Formation. N2-rich fluids do not appear to have been present in adjacent lithologies. Isotopic analysis of N2 in fluid inclusions and in the slates indicates that the N2 in the slates (thought to be present as substituting for K+ in muscovite and for Na+ in ) was probably originally derived from organic matter in the sediment and subsequently released to the fluid phase during metamorphism.

Mineral-fluid and fluid-phase equilibrium calculations show that the mineral assemblage in the slates could be in equilibrium with either N2-rich or aqueous fluid depending on redox conditions. The N2-rich and aqueous fluids in the veins could, therefore, have been trapped at different times under different conditions, though their coexistence as immiscible fluids is a possibility.
Fluid Inclusion Studies on the Ecton Hill Copper Deposits, North Staffordshire
Authors: Masheder R. , Rankin A. H.
Published: December 2006

Thermometric and D-ICP analysis of fluid inclusions in calcite and fluorite show that the fluids responsible for extensive carbonate-hosted copper mineralization in the Ecton Hill area were low-temperature (< 100 °C), high-salinity (19.5 to 23 wt. % NaCl equivalents) brines strongly enriched in calcium (mean Ca:Na wt. ratio = 1.9). Compared with the fluids responsible for classical ‘Mississippi Valley type’ lead-zinc deposits elsewhere in the south Pennine orefield, the Ecton ore-fluids were of lower temperature and slightly more enriched in potassium. Despite these subtle differences, the data are consistent with a basinal brine model for ore genesis in this western part of the orefield similar to that envisaged for the remainder of the orefield. These Ca-Na-K-Cl, copper-bearing brines were most probably derived from the Cheshire basin located to the west of the Derbyshire Dome.
The Occurrence of Robertsite in a Sedimentary Phosphate Ore from Thailand
Authors: Van Kauwenbergh Steven J. , Cooper-Fleck Michelle , Williams Marilyn R.
Published: December 2006

During a mineralogical study of guano-derived sedimentary phosphate ore from the Lamphun area of northwest Thailand, robertsite [Ca6(H2O)6Mn3+9O6(PO4)9.3H2O] was identified and concentrated to a level suitable for X-ray diffraction and chemical analysis. Robertsite has previously been described only in association with altered phosphatic pegmatites. This new occurrence in a phosphate deposit indicates that it may be found in a broad spectrum of sedimentary rocks.
Sieleckiite, a New Copper Aluminium Phosphate from Mt Oxide, Queensland, Australia
Authors: Birch W. D. , Pring A.
Published: December 2006

Sieleckiite is a new copper aluminium phosphate discovered at the Mt Oxide Copper Mine, 150 km north of Mt Isa, Queensland, Australia. It occurs with variscite, turquoise, libethenite and minor pseudomalachite in a fracture in a boulder of quartzite and shale. Sieleckiite forms deep sky blue to royal blue spheres up to 0.5 mm in diameter, made up of fibrous radiating crystals between 20 and 100 µm long and 1 to 2 µm wide. The mineral has a very pale blue streak and a pearly lustre on uneven fracture surfaces. Hardness is about 3 and the measured density is 3.02 g cm−3. The average of nine electron microprobe analyses gave CuO 32.39, Al2O3 26.57, P2O5 19.42%. Separate analyses gave H2O 18.1, CO2 1.6% (carbonate impurity). These data gave an empirical formula of Cu3.1Al4.0(PO4)2.1(OH)12.1.7H2O, calculated on the basis of 22 oxygen atoms. The simplified formula is Cu3Al4.0(PO4)2.1(OH)12.2H2O. The strongest lines in the X-ray powder diffraction pattern are {d(I)(hkl)}; 9.12(50)(100), 5.06(100)(101), 3.852(100)(111), 3.276(30)(2¯20), 2.827(50)(1¯02,102), 2.460(50)(3¯21). These data were indexed on a triclinic cell with a 9.41(8), b 7.56(5), c 5.95(6) Å, α 90.25(12)° β 91.27(12)° γ 104.02(7)° and a volume of 410.8(5) Å3. For Z = 1, the calculated density is 2.94 g cm−3. Optical properties could not be determined in full; the refractive indices are between 1.63 and 1.66, pleochroism is very weak from colourless to very pale blue.

The mineral is named for the discoverer, Robert Sielecki (1958- ). Type specimens are preserved at the Museum of Victoria and the South Australian Museum. Sieleckiite was approved by the IMA Commission on New Minerals and Mineral Names prior to publication.
A New Look at the Galim (a) and Galim (b) Meteorites
Authors: Michel-Lévy Mireille Christophe , Bourot-Denise Michèle
Published: December 2006

Small stones were recovered from a meteorite shower observed in Cameroon on November 13, 1952. The majority are LL6 specimens, Galim (a), but one is a chondrule-rich enstatite chondrite, Galim (b). Petrology and mineral chemistry were determined on polished sections of both types. Galim (a) has undergone multiple brecciation. During the first, chromite apparently recrystallized in healed fractures under more reducing conditions than those which prevailed when the silicates recrystallized. Galim (b) shows some features of petrologic type 3 but differs considerably from the other unequilibrated E chondrites. It is suggested that Galim (a) and Galim (b) belong to the same meteorite shower.
Nomenclature of Pyroxenes
Authors: Morimoto N. , Fabries J. , Ferguson A. K. , Ginzburg I. V. , Ross M. , Seifert F. A. , Zussman J. , Aoki K. , Gottardi G.
Published: December 2006

This is the final report on the nomenclature of pyroxenes by the Subcommittee on Pyroxenes established by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The recommendations of the Subcommittee as put forward in this report have been formally accepted by the Commission. Accepted and widely used names have been chemically defined, by combining new and conventional methods, to agree as far as possible with the consensus of present use. Twenty names are formally accepted, among which thirteen are used to represent the end-members of definite chemical compositions. In common binary solid-solution series, species names are given to the two end-members by the ‘50% rule’. Adjectival modifiers for pyroxene mineral names are defined to indicate unusual amounts of chemical constituents. This report includes a list of 105 previously used pyroxene names that have been formally discarded by the Commission.
The Petrology and Geochemistry of the St. David's Granophyre and the Cwm Bach Rhyolite, Pembrokeshire, Dyfed
Authors: Bloxam T. W. , Dirk M. H. J.
Published: December 2006

A petrological and geochemical study has been made of the late Precambrian St. David's granophyre (SDG) and the Cwm Bach rhyolites (CBR). The SDG is trondhjemitic, peraluminous, and chemically zoned with lower Na/K ratios in its interior portions. Although the SDG contains only minor amounts of K, the Rb content is relatively high and ratios of immobile versus mobile elements indicate that K has been removed. The CBR are flow-banded and autobrecciated subaerial rhyolite flows which are more K-rich and less altered than the SDG, lying close to the ternary minimum composition of the system Q-Or-Ab-(H2O). K mobility is considered to result from the reaction K-feldspar→ K-mica which released excess K ions, imparting peraluminous compositions to the rocks. On the basis of this reaction the original K content of the rocks has been estimated, the values for which are more compatible with immobile element abundances and with normal igneous trends. Similar abundances of the relatively immobile elements Ti, Zr, Sr, Y and Nb, together with K-corrected K/Rb ratios, suggest that the SDG and CBR may be comagmatic volcanic-arc-collision-type granite and rhyolite.
Differential Scanning Calorimetry of Minerals of the Dolomite-Ferroan-Dolomite-Ankerite Series in Flowing Carbon Dioxide
Authors: Dubrawski J. V. , Warne S. St. J.
Published: December 2006

The dolomite-ferroan-dolomite-ankerite series of carbonate minerals has been investigated in flowing carbon dioxide using high-temperature DSC. Decomposition products were analysed by X-ray diffraction. The minerals studied included dolomite containing no iron, and members substituted by iron in the molar ratio range of 0.082 to 0.49. Complete resolution of the three main endothermic features was observed and enthalpy values ΔH, determined from each. The individual and total enthalpy values showed a linear dependence upon the Fe and Mg content of the members across the series. A decrease in the enthalpy of decomposition occurs with increasing Fe content. The effect of Fe substitution was readily observed and the estimated limit of detection is less than 1% FeO. Accuracy of the measurements was limited by the purity of the minerals themselves.
Ashoverite, a New Mineral, and Other Polymorphs of Zn(OH)2 from Milltown, Ashover, Derbyshire
Authors: Clark A. M. , Fejer E. E. , Cressey G. , Tandy P. C.
Published: December 2006

Four polymorphs of Zn(OH)2 have now been recorded from an oxidised vein exposure near Milltown, Ashover, Derbyshire; sweetite, wülfingite, γ-Zn(OH)2, and ashoverite. The last is a new mineral, a tetragonal modification of Zn(OH)2 containing minor quantities of Pb, Cd and Ca. Its unit cell dimensions are a 6.825(2) and c 33.36(4) Å, giving V = 1554 Å3; Z = 32; space group I41/amd, I41md, or I4¯2d; Dmeas. 3.3, Dcalc 3.44 g cm−3. Ashoverite occurs as colourless platy crystals associated with fluorite; it is uniaxial positive with ω 1.629(2), ε 1.639(2). The chemical composition of sweetite is compared with that of ashoverite.
Alkali feldspars: ordering rates, phase transformations and behaviour diagrams for igneous rocks
Authors: Brown William L. , Parsons Ian
Published: December 2006

Homogeneous and heterogeneous phase relationships in the alkali feldspars are reviewed, and behaviour diagrams developed. Al,Si ordering is almost certainly continuous and higher order in both albite and potassium feldspar and has been established reversibly or nearly so down to below 500°C in albite and possibly to ∼ 200°C in potassium feldspar. The degree of order in intermediate albite changes strongly over a range of ∼ 75–150°C depending on pressure, low albite being stable up to about 620–650°C and high albite above about 725°C at low pressure. Symmetry is broken at ∼ 980°C mainly by a cooperative shearing of the whole framework and not by Al,Si ordering alone; there is a thermal crossover near 700°C shearing being dominant above (high albite) and ordering dominant below (intermediate albite).

In potassium feldspar symmetry is broken by Al,Si ordering at a temperature of about 500°C The change in degree of order with respect to temperature has been followed easily and reversibly in sanidine from ∼ 1075 to ∼ 550°C and to a lesser extent in microcline from 450 to 200°C. Ordering rates in sanidine down to 500°C and ordering rates in microcline between 450 and 200°C are almostas fast as in albite. Ordering in sanidine at 500°C and below slows and then stops with the development of the tweed orthoclase domain texture. The tweed texture acts as a barrier to further order because the strain energy associated with the (incipient) twin domain texture balances or nearly balances the free energy decrease resulting from ordering. Ordering stops not because of the kinetics of Al,Si diffusion, but because the totaldriving forceis very small or nil. Ordering can readily proceed to completion, with the formation of low microcline, only if the domain-texture barrier is overcome by processes involving fluids or strong external stresses. There is no barrier in albite.

The symmetry-breaking process in alkali feldspar changes with composition from mainly shearing in albite to ordering in potassium feldspar. Symmetry is broken equally at a compositional crossover (metastable with respect to exsolution) near Ab80-75at low pressure and progressively displaced towards Or at higher pressures. Ordering in pure albite occurs by a (nearly) one-step path which progressively becomes two-step with substitution of Or. Diagrams showing the near-equilibrium variation of the order parameters at low pressure with composition andTare given, as well as two extreme phase andbehaviourdiagrams for complete coherent and complete incoherent (strain-free) relationships. These diagrams can be used to understand feldspar relationships and microtextures in hypersolvus and subsolvus rocks, the occurrence of orthoclase, and of intermediate and low microcline.
Magma mixing in undersaturated alkaline volcanics, Cantal, Massif Central, France
Authors: Downes H.
Published: December 2006

Several examples of magma mixing exist within the undersaturated alkaline magma series of the Tertiary/Quaternary volcanics in the French Massif Central. This study describes magma mixing in the Puy Griou/Griounot area of the Cantal volcano (10-3 Ma). Petrographic evidence for injection of blebs of basic magma into phonolitic host magmas is abundant (cauliform inclusions, liquid-liquid contacts, vesiculation and chilling). Compositions of the inclusions are basic tephrite, whereas the hosts are miaskitic phonolites. Petrographic examination reveals the presence of disequilibrium mineralogical features (e.g. Mg-rich olivine in phonolites) and strong zoning in many clinopyroxenes. Transfer of phenocrysts between basic inclusions and phonolite hosts was common, and can be seen clearly in the wide range of compositions of clinopyroxene. Hornblende, magnetite and olivine were also transferred from inclusions to host.

Sr and Nd isotope data indicate that, unlike most other fractionated magmas of the region, phonolites which show evidence for magma mixing are uncontaminated by the continental crust and have isotopic ratios similar to local primitive basic magmas. This leads to the suggestion that the magma mixing event took place at great depth, rather than being a high-level phenomenon. The phonolites were thus generated by high-pressure fractional crystallisation of an earlier basanitic or tephritic parent, perhaps at upper-mantle depths. This conclusion may explain why some phonolites elsewhere in the world have entrained spinel Iherzolite mantle xenoliths.
Zoning in granitoid accessory minerals as revealed by backscattered electron imagery
Authors: Paterson B. A. , Stephens W. E. , Herd D. A.
Published: December 2006

Accessory minerals are often difficult to investigate with light optics as the mineral grains tend to be small and the refractive indices high. Textural features due to variations in composition are well displayed in such minerals by backscattered electron imagery under circumstances designed to select only the composition contribution to electron backscattering and displayed as atomic number (Z)-contrast imagery (ZCI). It is shown by this technique that compositional zonation patterns are very common and sector zoning in titanite is described for the first time. The compositional basis for zonation of titanites in this study is shown to be controlled by coupled substitutions involving the REE. The technique is particularly good at revealing rounded cores to zircon grains which are normally taken to be refractory grains from the magma source region, and ZCI studies may improve targeting of grains for U-Pb geochronological investigations. Several examples are presented of applications of the technique to accessory minerals encountered in polished thin sections of granitoids in the Caledonian of Scotland. The consequences of ZCI studies for trace element modelling of REE in granitoid petrogenesis are discussed.
Vaughanite, TlHgSb4S7, a new mineral from Hemlo, Ontario, Canada
Authors: Harris Donald C. , Roberts Andrew C. , Criddle Alan J.
Published: December 2006

Vaughanite, idealized formula T1HgSb4S7, is a very rare primary constituent of the Golden Giant orebody of the Hemlo gold deposit, Hemlo, Ontario, Canada. It was found in two polished sections from one drill core; as a 450 by 300 µm aggregate associated with pääkkönenite, stibnite, realgar, and native arsenic; and as a 40 µm anhedral grain associated with stibarsen and chalcostibite. Vaughanite is opaque with a metallic lustre and a black streak. No cleavage was observed but parting, produced by indentation, was detected as a series of weak parallel traces. It is brittle, with an even, occasionally arcuate, fracture. VHN25 is 100–115, mean 104. Mohs hardness (calc.) = 3−3½. In refected plane-polarized light in air the bireflectance is weak to moderate; the pleochroism is also weak, from a somewhat greenish grey to slightly darker bluish grey. Anisotropism is moderate to strong, with rotation tints in shades of green, yellow, purplish brown to brown. Reflectance spectra and colour values are tabulated. The colour in air is light grey. Internal reflections are rare but are arterial-blood-red on indentation fractures. X-ray studies have shown that vaughanite is triclinic with refined unit-cell parameters a 9.012 (3), b 13.223 (3), c 5.906 (2) Å, α 93.27 (3)°, β 95.05 (4)°, γ 109.16 (3)°, V 659.46 (80) Å3, a:b:c = 0.6815 : 1 : 0.4466 and Z = 2. The space group choices are P1 (1) or (2), diffraction aspect P*. The five strongest lines in the X-ray powder pattern [d in Å (l) (hkl)] are: 4.343 (30) (), 4.204 (100) (), 3.313 (60) (130), 2.749 (40) (, 131) and 2.315 (30) (, 122). The average of five electron microprobe analyses gave T1 18.3 (2), Hg 17.5 (2), Sb 43.4 (3), As 1.1 (1), S 20.5 (5), total 100.8 wt. %, corresponding, on the basis of total atoms = 13, to T10.98Hg0.95(Sb3.90As0.17)Σ4.07S7.00. The calculated density is 5.56 g/cm3 for the empirical formula and 5.62 g/cm3 for the simplified formula. The mineral is named for Professor David J. Vaughan.
Transmission electron microscopy of coexisting low-tridymite polymorphs
Authors: Ashworth J. R.
Published: December 2006

Three polymorphs of tridymite (MC, PO-10 and MX) have been examined by transmission electron microscopy (TEM), in crystals which also contain lamellae of cristobalite. MX is the least common, and is highly unstable in the electron beam. It occurs as small regions (< 1 µm2) in PO-10 tridymite and at MC/PO-10 boundaries; these regions are interpreted as being strained. A consistent association between PO-10 and the cristobalite lamellae is attributed to the fact that PO-10 can more closely match the low-cristobalite structure than MC can, at boundaries parallel to the plane in which the crystal structures contain layers of SiO4 tetrahedra. An analogous interpretation explains the observation that twin boundaries (associated with 60° or 120° rotation of the layer) are commonly parallel to the layer plane in PO-10 but at high angles to it in MC. Abundant lamellar features, parallel to the same plane in PO-10, are tentatively interpreted as representing twinning by reflection and 180° rotation, which may also account for c* streaking in diffraction patterns.
Thorium–bitumen mineralization in Silurian sandstones, Welsh Borderland
Authors: Parnell John , Eakin Paul
Published: December 2006

The Llandovery Folly Sandstone near Presteigne, Powys, contains disseminated thorium mineralization. The thorium occurs as inclusions of thorite and thorianite within sub-millimetre-scale bitumen nodules throughout the sandstone. The nodules grew replacively in situ. The two square kilometres outcrop/subcrop of the sandstone may contain over 500 tonnes thorium.
Spectral mineralogy of terrestrial planets: scanning their surfaces remotely
Authors: Burns Roger G.
Published: December 2006

Spectral measurements of sunlight reflected from planetary surfaces, when correlated with experimental visible-near-infrared spectra of rock-forming minerals, are being used to detect transition metal cations, to identify constituent minerals, and to determine modal mineralogies of regoliths on terrestrial planets. Such remote-sensed reflectance spectra measured through earth-based telescopes may have absorption bands in the one micron and two micron wavelength regions which originate from crystal field transitions within Fe2+ ions. Pyroxenes with Fe2+ in M2 positions dominate the spectra, and the resulting 1 μm versus 2 µm spectral determinative curve is used to identify compositions and structure-types of pyroxenes on surfaces of the Moon, Mercury, and asteroids, after correcting for experimentally-determined temperature-shifts of peak positions. Olivines and Fe2+-bearing plagioclase feldspars also give diagnostic peaks in the 1 µm region, while tetrahedral Fe2+ in glasses absorb in the 2 µm region as well. Opaque ilmenite, spinel and metallic iron phases mask all of these Fe2+ spectral features. Laboratory studies of mixed-mineral assemblages enable coexisting Fe2+ phases to be identified in remote-sensed reflectance spectra of regoliths. Thus, noritic rocks in the lunar highlands, troctolites in central peaks of impact craters such as Copernicus, and high-Ti and low-Ti mare basalts have been mapped on the Moon's surface by telescopic reflectance spectroscopy. The Venusian atmosphere prevents remote-sensed spectral measurements of its surface mineralogy, while atmospheric CO2 and ferric-bearing materials in the regolith on Mars interfere with pyroxene characterization in bright- and dark-region spectra. Reflectance spectral measurements of several meteorite types, including specimens from Antarctica, are consistent with a lunar highland origin for achondrite ALHA 81005 and a martian origin for shergottite EETA 79001, although source regions may not be outermost surfaces of the Moon and Mars. Correlations with asteroid reflectance spectra suggest that Vesta is the source of basaltic achondrites, while wide ranges of olivine/pyroxene ratios are inconsistent with an ordinary-chondrite surface composition of many asteroids. Visible-near-infrared spectrometers are destined for instrument payloads in future spacecraft missions to neighbouring solar system bodies.
Surface alteration of pentlandite and spectroscopic evidence for secondary violarite formation
Authors: Richardson S. , Vaughan D. J.
Published: December 2006

Synthetic pentlandite surfaces were subjected to oxidation by a range of inorganic oxidants, and the resultant alteration of the surface studied by a range of surface-sensitive spectroscopic techniques. The oxidants used were air during heating to relatively low temperatures (150°C), steam, ammonium hydroxide, hydrogen peroxide, and sulphuric acid. Electrochemical oxidation was also undertaken. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), conversion electron Mössbauer spectroscopy (CEMS), and spectral reflectance measurements were used to characterize the surface compositions. New data for the binding energies of core electrons in pentlandite and violarite, based on the fitted XPS spectra, are proposed. For pentlandite and violarite respectively, values of 707.3 eV and 708.4 eV for the Fe 2p3/2, 853.0 eV and 853.2 eV for the Ni 2p3/2, and 161.2 eV for the S 2p in both sulphides, were obtained. After oxidation the pentlandite surfaces indicated nickel enrichment in the subsurface, with the formation of violarite. The immediate oxidized surface, of approximately 10Å thickness, indicated a range of iron oxides and hydroxides (Fe3O4, Fe2O3 and FeOOH, with possible Fe1−xO and Fe(OH)3), nickel oxide (NiO), and iron sulphates (FeSO4, Fe2(SO4)3). The proportions of the phases present in the surface layer are inferred to be a consequence of both the strength of the oxidant employed, and the thermodynamic stability of the phases, as can be illustrated using partial pressure and Eh/pH diagrams. A sequence of oxidation is proposed, accounting for the sub-surface enrichment in violarite, and the development of the oxidized surface, which is inferred to have a major affect on the rates of oxidation.
Zincian högbomite as an exploration guide to metamorphosed massive sulphide deposits
Authors: Spry Paul G. , Petersen Erich U.
Published: December 2006

Zincian högbomite (ZnO 3.5–10.5wt.%) occurs as an accessory phase in garnet quartzite that is intimately associated with the Broken Hill and Black Mountain Cu-Pb-Zn-Ag deposits, Aggeneys, South Africa. Högbomite coexists with a number of minerals including quartz, gahnite, sillimanite, sphalerite, pyrrhotine, pyrite, magnetite, and ilmenite, suggesting that högbomite may have formed by sulphidation and oxidation reactions. Such reactions may account for the high Zn content of högbomite. Where associated with metamorphosed massive sulphide deposits högbomite is enriched in Zn relative to that found in ultramafics, Fe-Ti deposits, Fe ores, aluminous metasediments, and skarns. This enrichment in högbomite constitutes a potential exploration guide for metamorphosed massive sulphide deposits.
Members of the freibergite–argentotennantite series and associated minerals from Silvermines, County Tipperary, Ireland
Authors: Zakrzewski Marek A.
Published: December 2006

Ore microscope and electron microprobe investigations on Zn-Pb-Ag ores from B Zone in Silvermines, Ireland, have shown the presence of two As-Sb-Ag phases; a tetrahedrite-group mineral with composition Cu6.3Ag3.7Fe0.9Zn1.2As2.2Sb2.1S12.7 and proustite-pyrargyrite (Ag3As0.5Sb0.5S3). It is postulated that both phases inherited their As and Sb from primary geocronite (Pb14.5As3.4Sb2.6S23) and that they are metastable. An enrichment in Ni in the ores is due to very fine to submicroscopic intergrowths of gersdorffite (Ni0.6Fe0.4AsS) with geocronite and with galena.
Manganoan fayalite and products of its alteration from the Strzegom pegmatites, Poland
Authors: Janeczek J.
Published: December 2006

Nodules of manganoan fayalite occur in schlieren pegmatities in the vicinity of Strzegom, Lower Silesia. The fayalite, Na0.02(Fe1.812+Mn0.16Mg 0.03)Si0.99O4, is unzoned and non pleochroic. 2Va = 42° a 4.826(3), b 10.500(2), c 6.102(2) A, d130obs. = 2.83 Å, d130calc. = 2.833 Å, D = 4.35 g cm-3, Dcalc. = 4.353 g cm-3. The role of Na+ ions in the fayalite chemistry is discussed. The fayalite underwent multi-stage hydrothermal alteration beginning at the highest temperature (440°C) of homogenization of gaseous-fluid inclusions in quartz adjacent to the fayalite grains. Increase in fO2 and then in PH2O resulted in the formation of magnetite-quartz and Mn-grunerite-magnetite-quartz aggregates within the fayalite grains. The fayalite is mantled by a Mn-greenalite-magnetite rim, Mn-grunerite-magnetite-Mn-minnesotaite zone in a stilpnomelane or greenalite-rich groundmass. The minnesotaite is believed to have formed at the expense of grunerite. Stilpnomelane, the most abundant silicate phase in the rim, is the product of biotite and presumably greenalite alteration at the second stage of increasing Na activity (the crystallization of cleavelandite) in the pegmatites. The fayalite is also heavily altered to iddingsite—a composite mixture of amorphous FeOOH and silica. The iron-hydroxide recrystallized partially to poorly-crystalline goethite.
Origin and development of flexibility in asbestiform fibres
Authors: Germine M. , Puffer J. H.
Published: December 2006

Quantitative measurement of relative flexibility have been made on amphibole fibres based on calculation of bending strain of maximally bent fibre segments. Enhanced flexibility was found to be an inverse function of fibre diameter. Asbestos is therefore a morphological entity. These conclusions are supported by consistent observations of fibre diameter/flexibility relationships in amphiboles, serpentine, and rutile. Flexibility may arise from growth of thin crystals (primary flexibility), or from crystal diameter reduction (secondary flexibility). Mechanisms for secondary flexibility in amphiboles include splitting and solution along cleavage planes. Gross morphological characteristics are a poor indicator of microscopic habit, since coarsely fibrous minerals such as picrolite antigorite may not be fibrous after particle width reduction, and secondary asbestiform fibres are often derived from minerals with a non-fibrous morphology on gross examination.
Oxygen isotope fractionation between cassiterite and water
Authors: Alderton David H. M.
Published: December 2006

Analysis of stable isotopes in coexisting minerals has found wide application in the study of hydrothermal mineral deposits, particularly for elucidating the temperature and source of the fluid phase involved in mineralisation. For these purposes the temperature dependence of isotopic fractionation in several mineral-water systems has already been established (e.g. Friedman and O'Neil, 1977; O'Neil, 1986). Unfortunately, the oxygen isotope fractionation between cassiterite (SnO2) and water has not been adequately characterized, and this has hindered a full utilization of oxygen isotope data derived from studies of tin deposits (e.g. Harzer, 1970; Patterson et al., 1981; Kelly and Rye, 1979). Because of this situation, an attempt is made here to derive a relationship between temperature and the fractionation of oxygen isotopes (Δ) between quartz and cassiterite, based on the fractionations observed in naturally-occurring assemblages and independent temperature estimates.
Högbomite from the Aldan Shield, Eastern Siberia, USSR
Authors: Grew Edward S. , Drugova Galina M. , Leskova N.V.
Published: December 2006

Högbomite, a complex oxide of A1, Fe, Mg, and Ti, is an important constitutent of some iron ores and emery deposits as well as an infrequent accessory in aluminous high-grade rocks (e.g. Grew et al., 1987). The recent increase in reports of new localities (e.g. Rammlmair et al.,1988) suggests that högbomite may be more widespread than is generally perceived. We report here högbomite from the Aldan Shield, Eastern Siberia. This högbomite is remarkable for the wide variation in composition measured in a single thin section. Our report is only the second from the USSR of högbomite for which chemical data are given.
Carbonatite-related contact metasomatism in the Fen complex, Norway: effects and petrogenetic implications
Authors: Andersen Tom
Published: December 2006

In the Fen complex (Telemark, S.E. Norway), carbonatites of different compositions have penetrated feldspathic fenites (alkali feldspar(s) + aegirine augite ± alkali amphibole) or older carbonatites, inducing different types of contact metasomatic alterations in their wall-rocks. (1) Pyroxene søvite has induced alkali metasomatism (i.e. fenitization s.s.), with alkali feldspars remaining stable and aegirine-augite transformed to nearly pure aegirine. (2) Søvite and dolomite carbonatite with phlogopite and/or alkali or alkali-calcic amphibole have caused replacement of feldspathic fenite by phlogopite, i.e. magnesium metasomatism. (3) Granular (dyke facies) ferrocarbonatite has increased the ferromagnesian components in calcite in wall-rock søvite. (4) Heterogeneous (pyroclastic) ferrocarbonatite induced pseudomorphic replacement of phlogopite by chlorite (leaching of alkalis). The different contact metasomatic processes reflect contrasts in compositional character among carbonatite magmas in the Fen complex, which may be evaluated in terms of differences in alkali and magnesium carbonate activities. The different types of carbonatite magma represent the products of local evolutionary trends, and are genetically related to spatially associated silicate rocks, rather than to a single ‘primitive’ carbonatite parent magma.
Compositional relations in Li-micas from S.W. England and France: an ion- and electron-microprobe study
Authors: Henderson C. M. B. , Martin Joanna S. , Mason R. A.
Published: December 2006

A combination of ion-microprobe (for Li) and electron-microprobe (for other major elements including F) methods has been used to analyse Li-rich micas from the S.W. England batholith (mainly the St Austell granite) and the Massif Central, France. Rocks showing various degrees of hydrothermal alteration were studied in order to separate the original compositional trends from alteration trends. The original compositional trend is essentially one of increasing Li with increasing degree of evolution. The main atomic substitution in the original micas is 3Li substituting for A1 and 2 vacancies in octahedral sites; substitution of Li for R2+ (Fe, Mn, Mg) in octahedral co-ordination is generally subordinate. Alteration trends involve a loss of Li, Fe, F, Rb and Cs, and a gain in A1. The effects of volatile elements on phase relations of granites are reviewed and it is concluded that the original Li-micas were primary, i.e. crystallized from the melt. It is suggested that the late-magmatic stage passed transitionally into the hydrothermal stage leading inevitably to subsolidus recrystallization (autometasomatism) of the primary minerals, so introducing further textural and mineralogical complexities to the rocks.
Mösbauer spectroscopic study of the decomposition mechanism of ankerite in CO2 atmosphere
Authors: Milodowski A. E. , Goodman B. A. , Morgan D. J.
Published: December 2006

Mössbauer spectroscopy has been used to identify the iron-containing products that are formed during the thermal decomposition of ankerite in a CO2 atmosphere. The decomposition takes place in three stages and evidence is produced to show that the first stage involves decomposition of ankerite to yield a periclase-wustite solid solution, (Mg,Fe)O, along with calcite and CO2, the periclase-wustite then reacting with CO2 to produce magnesioferrite (MgFe2O4) and CO. In the second stage the magnesioferrite and calcite react to produce periclase and dicalcium ferrite. The third stage does not involve reaction of Fe-containing phases and corresponds to the decomposition of calcite to CaO.
Vochtenite, (Fe2+,Mg)Fe3+[UO2/PO4]4(OH). 12–13 H2O, a new uranyl phosphate mineral from Wheal Basset, Redruth, Cornwall, England
Authors: Zwaan P. C. , Arps C. E. S. , de Grave E.
Published: December 2006

Vochtenite, a new mineral from the Basset Mine, southeast of Camborne in Cornwall, England, is a ferrous-ferric magnesium-bearing hydroxy uranyl phosphate mineral. It is monoclinic with a = 12.606, b = 19.990, c = 9.990 Å, β = 102.31° Z = 3; the ideal formula is:

The strongest lines in the X-ray powder diffraction pattern are: 9.998(100)(020), 4.999(30)(040), 4.892(45)(002), 3.475(70)(311), 3.333(50)(060), 3.087(40)(232), and . Vochtenite is brown in colour with a bronzy lustre and is non-fluorescent. Mohs hardness is 2.5 and the density (calc.) = 3.663 g/cm3. There is a prominent (010) cleavage. Vochtenite is optical biaxial negative, 2V (calc.) = 89(3)° its dispersion is indiscernible. Refractive indices are α = 1.575(2), β = 1.589(2), γ = 1.603(2), and the pleochroism is very weak. Orientation X(α)∥b is perpendicular to (010) and Z(γ)∧c is small. The mineral occurs as subparallel (0.5–1.0 mm) crystal aggregates with a pseudo-quadratic outline. The mineral is named vochtenite after Prof. Dr. Ing. R. F. C. Vochten of the State University of Antwerpen, Belgium.
Synthesis and stabilities of the basic copper(II) chlorides atacamite, paratacamite and botallackite
Authors: Pollard A. M. , Thomas R. G. , Williams P. A.
Published: December 2006

Strictly reproducible syntheses of the trimorphs of composition Cu2Cl(OH)3, atacamite, paratacamite, and botallackite, have been developed. In syntheses involving direct precipitation, or reaction of aqueous solutions with solid phases, reliable results are obtained only if the temperature and time of reaction are carefully controlled. Botallackite, the rarest of the naturally occurring trimorphs, is a key intermediate and crystallizes first under most conditions; subsequent recrystallization of this phase to atacamite or paratacamite, or of the latter from the former, depends upon the precise nature of the reaction medium. The crystallization sequence indicates that paratacamite, as has long been suspected, is the thermodynamically stable phase at ambient temperatures. Spertiniite, Cu(OH)2, can be reproducibly synthesized via one route in the non-commutative titration of aqueous copper chloride with aqueous sodium hydroxide solutions.
Mineral nomenclature: zirconolite
Authors: Bayliss Peter , Mazzi Fiorenzo , Munno Rosalba , White Tim J.
Published: December 2006

The nomenclature of CaZrTi2O7 minerals has become very confused, such that zirconolite, zirkelite and polymignite each have acquired multiple meanings and represent five different crystal structures. To resolve these inconsistencies, the IMA approved resolutions as follows. Zirconolite is the non- crystalline (metamict) mineral or mineral with undetermined polytypoid of CaZrTi2O7. Zirconolite-3O is the three-layered orthorhombic polytypoid of CaZrTi2O7. Zirconolite-3T is the three-layered trigonal polytypoid of CaZrTi2O7. Zirconolite-2M is the two-layered monoclinic polytypoid of CaZrTi2O7. Polymignite (metamict) is discarded as equivalent to zirconolite. Zirkelite is the cubic mineral with formula (Ti,Ca,Zr)O2−x.