bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of the ammonium ion in pegmatites, aplites and their minerals from central northern Portugal
Authors: Hall A. , Neiva A. M. R.
Published: December 2006

The ammonium content of pegmatites, aplites and granites from Alijó-Sanfins, northern Portugal, averages 162, 109 and 159 ppm respectively. There is no systematic difference in the NH4/K ratio between these rocks, and the variation in their ammonium content is mainly due to variations in the amount of potassium minerals they contain. The K-feldspars have higher NH4+ contents than the muscovites, but lower NH4/K ratios. The preference of NH4+ for micas rather than feldspars is not as great as that shown by rubidium. The ammonium content of pegmatites in general is highly variable, and is largely determined by the nature of the granites with which they are associated.
Precious and base metal selenide mineralization at Hope's Nose, Torquay, Devon
Authors: Stanley C. J. , Criddle A. J. , Lloyd D.
Published: December 2006

Precious and base metal selenide minerals have been identified in gold-bearing carbonate veins cutting Middle Devonian limestones of the Torquay Limestone Group at Hope's Nose, Torquay. The selenide assemblage consists of clausthalite (PbSe), tiemannite (HgSe), klockmannite (CuSe), umangite (Cu3Se2), tyrrellite (Cu,Co,Ni)3Se4, trustedtite (Ni3Se4), penroseite (NiSe2), naumannite (Ag2Se), eucairite (AgCuSe) and fischesserite (Ag3AuSe2), only clausthalite having previously been reported from Britain. They are associated with palladian gold, gold, hematite, and accessory pyrite and chalcopyrite in a gangue consisting predominantly of calcite; alteration products include cerussite, malachite, aragonite and goethite.

The relative abundance of Au, Ag, Hg and Se is a characteristic feature in the uppermost parts of some precious metal ‘epithermal’ systems. The occurrence at Hope's Nose is related to both structural and lithological factors: a deep-seated NW-SE structural lineament, the Lundy-Sticklepath-Lustleigh-Torquay fault; local thrusting, and to an association of basic-intermediate igneous rocks with a sedimentary sequence including carbonaceous shales and limestones. The mineralization is considered to be post-Variscan, probably Permo-Triassic in age.
Optical absorption spectroscopy of doped materials: the P213-P212121 phase transition in K2(Cd0.98Co0.02)2(SO4)3
Authors: Percival M. J. L.
Published: December 2006

The use of optical absorption spectroscopy for the study of the changes in local distortions during phase transformations is discussed, with particular reference to the P213-P212121 transition in K2Co2(SO4)3 langbeinite. In order to extend this technique to the study of cobalt-doped cadmium langbeinite, K2Cd2(SO4)3, the consequences of the doping with regard to site occupancies and low signal strength are discussed, and some details of data modelling are considered. The problem of modelling the spectrum of Finero sapphirine is taken as an example, and it is shown that even simple and evidently inadequate models can provide useful information.

The results of optical spectroscopic investigation of the P213-P212121 transition in K2(Cd0.98Co0.02)2(SO4)3 langbeinite are presented. The trigonal splitting of the spin allowed 4T1g(F)-4T1g(P) transition has been determined, and shows a linear increase with increasing temperature in the high temperature cubic phase, and a constant value in the low temperature phase. This is in good agreement with previous structural work on this material, and it is concluded that optical spectroscopy of doped materials can provide useful information about site distortions.
Overcoming the problems of high-resolution transmission electron microscopy of biogenic aragonite
Authors: Ness S. E. , Haywick D. W. , Cuff C.
Published: December 2006

High-resolution transmission electron microscopy of biogenic carbonate minerals is hampered by a lack of stability during exposure to the electron beam. However, aragonite in bivalve shells may be successfully imaged using a modification of the ‘minimal-exposure technique’ of Williams and Fisher (1970). Diffraction patterns taken before and after beam exposure indicate that the aragonite remained stable during imaging. The procedure described here should prove useful for further studies of the ultrastructure and/or the diagenesis of biogenic carbonate minerals.
Damaraite, a new lead oxychloride mineral from the Kombat mine, Namibia (South West Africa)
Authors: Criddle A. J. , Keller P. , Stanley C. J. , Innes J.
Published: December 2006

Damaraite, ideally 3PbO.PbCl2, is a new mineral which occurs with jacobsite, hausmannite, hematophanite, native copper, an unnamed Pb-Mo oxychloride, calcite, and baryte, in specimens from the Asis West section of the Kombat mine, Namibia (South West Africa). Damaraite is colourless and transparent with a white streak, and adamantine lustre. It is brittle with an irregular to subconchoidal fracture and a cleavage on (010). The mineral has a low reflectance, a weak bireflectance, barely discernible reflectance pleochroism, from grey to slightly bluish grey in some sections, and is weakly anisotropic. Reflectance data in air and in oil are tabulated. Colour values relative to the CIE illuminant C for the most strongly bireflectant grain are, for R1 and R2 respectively:

It has a VHN50 of 148 (range 145–154) with a calculated Mohs hardness of 3. X-ray powder diffraction studies give the following parameters refined from the powder data: orthorhombic; space group Pma2, Pmam or P21am; a 15.104(1), b 6.891(1), c 5.806 (1)Å; V is 604.3 (4)Å3 and Z = 3. Dcalc 7.84 g/cm3. The strongest six lines of the powder pattern are [d in Å (I) (hkl)]: 2.902 (10) (121,002); 2.766 (10) (510,221); 2.877 (9) (411); 3.164 (6) (401); 3.135 (6) (220); 1.747 (b) (313,721,531). The name is for the Damara sequence which hosts the Kombat deposit.
An applied mineralogical investigation of concrete degradation in a major concrete road bridge
Authors: Macleod G. , Hall A. J. , Fallick A. E.
Published: December 2006

A core of concrete taken from a major road bridge in the Strathclyde Region, Scotland, has been subjected to an applied mineralogical investigation, which involved stable isotope analysis, petrography, X-ray diffraction and scanning electron microscopy.

The structure is actively undergoing severe degradation due to mineral growth which is related to chemical reactions between the concrete and pore fluid. The physical growth of minerals causes disfigurement and structural weakening.

Pyrite and pyrrhotine hosted by dolerite aggregate appear to have been oxidized, providing sulphate for the deposition of ettringite and minor gypsum, in spheroidal cavities within the cement paste. The rainwater which passes through the structure mobilising sulphate from original gypsum in the paste and oxidizing the iron sulphides is also involved in the further leaching of elements from the cement paste and in the deposition of calcite. The isotopic values of calcites forming a crust on the concrete and a stalactite under the bridge are similar with δ13C= −19‰ PDB and δ18‰= +16‰ SMOW. We suggest that atmospheric carbon dioxide was the carbon source. The carbon isotopic fractionation of −12‰ from atmospheric carbon dioxide of δ13C= −7‰, (O'Neil and Barnes, 1971) can best be explained as due to a kinetic fractionation related to the hyper-basicity of the pore water. The equilibrium formation temperature of about 45°C calculated from the oxygen isotope values and assuming a δ18O value of meteoric water of −8‰ SMOW, is considered unreasonable. The exceptionally low δ18O values are attributed mainly to reaction kinetics and the calcite inheriting its oxygen, two-thirds from atmospheric carbon dioxide and one third from the meteoric formation water (O'Neil and Barnes, 1971). A δ18O value of atmospheric carbon dioxide of +41‰ SMOW and a δ18O value of meteoric water of −8‰ SMOW, lead to a calculated δ18O value for the calcites of +10‰ SMOW. The calcites analysed have a value of +16‰ and this may be due to partial re-equilibration towards a calculated value of +21‰ for calcite in equilibrium with the meteoric water at 20°C.
Geothermometry and Geobarometry—introduction
Authors: Yardley B. W. D. , Schumacher J. C.
Published: December 2006

The following four papers are a representative subset of the talks that were given during a lively session at the 1989 Winter Meeting of the Mineralogical Society (19 and 20 December), organised by us on behalf of the Metamorphic Studies Group on the theme of ‘Geothermometry and Geobarometry’. The talks at the meeting fell broadly into three groups: those dealing with fundamental problems of obtaining the requisite compositional and thermodynamic data, case studies of the applications of thermometers and barometers, and discussions of the limitations of the approach imposed by kinetic factors.

The first group of talks included contributions by T. J. B. Holland and J. Lieberman (co-authors M. Engi and R. G. Berman) dealing with perhaps the major hurdle in the way of reliable geothermometry and geobarometry: the question of activity-composition relationships for natural minerals. Holland took the examples of the pyroxenes and the plagioclase feldspars and showed, respectively, how Landau theory could be utilised to take account of ordering, and how Darken's quadratic formalism can take account of a structural break.
Empirical ferric iron corrections: necessity, assumptions, and effects on selected geothermobarometers
Authors: Schumacher John C.
Published: December 2006

The ferromagnesian silicate minerals, such as garnets, pyroxenes, micas, and amphiboles, appear in a variety of geothermometers and geobarometers. Where complete chemical analyses are available and regardless of bulk composition (metamorphosed pelitic or mafic), the aforementioned minerals commonly contain ferric iron. In mineral analyses using the electron microprobe, ferric and ferrous iron are not distinguished, and all the iron is treated as FeO. In ferric Fe-bearing minerals, this treatment results in (1) low analytical sums and (2) excess cations in the mineral formulae. Assuming ideal stoichiometry (ideal formula cations and oxygens) allows direct ferric estimates in garnets and pyroxenes; amphiboles require additional assumptions concerning site occupancies, and, for micas, no acceptable constraint exists for a ferric estimate. Based on ferric iron determinations for some metamorphic ferromagnesian silicates, the proportion of ferric to total iron increases at higher XMg values. The influence of ferric estimates on T and P calculations depends on the model used and on the extent the ferric estimate alters the relative proportions of end-members. Several examples suggest that, in general, if ferric estimates (or determinations) are made, they should be made for all the relevant minerals.
Geothermometry and geobarometry of high-grade rocks: a case study on garnet-pyroxene granulites in southern Sri Lanka
Authors: Faulhaber S. , Raith M.
Published: December 2006

In the central granulite belt of Sri Lanka, garnet-pyroxene granulites of granitic and gabbro-noritic composition are the most abundant rock types. The micro-structures and mineral chemistry data prove complete attainment of textural and large-scale chemical equilibrium during and following a phase of extreme penetrative deformation at conditions of the granulite facies (800–850 °C, 5 to 9 kbar). On a local scale, especially along the intergranular system, continued cation exchange decoupling from the early ceasing net-transfer reactions destroyed the near-peak metamorphic equilibrium. The extreme compositional variation of the coexisting ferro-magnesian phases (Fe/(Fe + Mg): gar 0.98−0.65, opx 0.92−0.40, cpx 0.88−0.28) and the near-isothermal conditions of equilibration throughout the studied area enabled examination of the effects of non-ideal mixing in garnet and pyroxenes on the equilibrium constants of reactions used in geothermobarometry, and tests on the quality of commonly applied thermometers/barometers and the validity of activity models adopted in the calibrations. The Sri Lankan data set reveals more or less pronounced compositional dependences for all of the tested gar-opx/gar-cpx Fe-Mg exchange thermometers and the opx + plg ⇌ gar + qtz barometers. Evidently the recommended solution models do not adequately describe the mixing properties of the involved ferro-magnesium mineral phases (garnet, orthopyroxene and clinopyroxene).
Thermal and kinetic constraints on the tectonic applications of thermobarometry
Authors: Crowley Peter D.
Published: December 2006

Metamorphic petrology, and in particular quantitative thermobarometry, offer the possibility of identifying faults in metamorphic terrains by the metamorphic and/or thermobarometric breaks that occur across them. Furthermore, the sense of the thermobarometric break (e.g. warmer, deeper rocks on top of colder, shallower ones) and its magnitude could be useful tools for determining the sense and magnitude of the fault. The sensitivity of thermobarometry to tectonic variables such as fault throw and uplift rate, has been tested by a series of one-dimensional numerical re-equilibration models for both thrust and normal faults. In each of these models, the post-tectonic re-equilibration of a model garnet-biotite geothermometer is simulated by coupling one-dimensional numerical thermal and garnet diffusion models. After cooling and uplift, a thermobarometric temperature was calculated by using a near-rim garnet composition (5–10 µm from the rim) calculated by the re-equilibration model and biotite from the model matrix. The models varied the thermal structure of the model orogen prior to faulting, the depth of the fault, the structural throw of the fault, and the uplift rate following faulting.

All models produced zoned garnet porphyroblasts that recorded P-T conditions that were different from those at the time of fault motion. Most of the models produced thermobarometric breaks that were in the same sense as the temperature break at the time of fault motion. Normal faults produced a normal thermobarometric gradient with higher temperatures recorded below the fault than above it. Many, but not all of the thrust models produced a thermobarometric inversion near the fault, with higher temperatures locally recorded above the fault than below it. However, the magnitude of thermobarometric break correlated poorly with the fault throw. Most models developed thermobarometric breaks that were much smaller than the breaks that existed at the time of fault motion. The size of the thermobarometric break was commonly of the same magnitude as would be generated from microprobe analytical error. The models suggest that for metamorphic rocks whose thermal peak does not exceed a narrowly defined closure temperature, thermobarometry faithfully recorded the P-T conditions of the metamorphic peak. The closure temperature increases slightly with increasing uplift rate, but overall is rather insensitive to the uplift rate or other tectonic variables. For rocks whose thermal peaks is above the closure temperature, however, the model thermobarometer recorded a temperature that was very close to the closure temperature.
Temperature-HF fugacity trends during crystallization of calcite carbonatite magma in the Fen complex, Norway
Authors: Andersen Tom , Austrheim Håkon
Published: December 2006

Calcite carbonatite (søvite), associated apatite cumulates and contact metasomatic phlogopite-rocks in the Fen complex (S. Norway) contain coexisting apatite and phlogopite. Two distinct compositional groups are recognized: fluorapatite (XF= 0.5–0.8) coexists with hydroxy-phlogopite withXF= 0.11–0.26, whereas hydroxyapatite (XF= 0.34–0.44) coexists with low-F hydroxy-phlogopite (XF≈ 0.03). Apatite-biotite geothermometry suggests that the minerals equilibrated at igneous temperatures (less than 1200 toca.625 °C), and were not significantly disturbed by late low-temperature re-equilibration. This, combined with HF-barometry based on apatite-fluid and phlogopite-fluid F-OH exchange equilibria, makes it possible to recognize two crystallization trends at different levels of hydrogen fluoride fugacity. The existence of such trends reflects internal buffering of the HF fugacity by apatite and/or phlogopite. The recorded differences in HF fugacity suggest that two or more independent or semi-independent lines of magmatic descent gave rise to calcite carbonatite magma in the Fen complex. Combined apatite-phlogopite geothermometry and hydrogen fluoride barometry is a useful tool enabling us to see through post-magmatic alteration of carbonatites, and to establish primary magmatic controls even in cases where carbonate and iron-titanium oxide minerals have re-equilibrated at much lower temperatures.
Silicate mineralogy of the Behelvie cumulates, N E Scotland
Authors: Wadsworth W. J.
Published: December 2006

Ultramafic, troctolitic and gabbroic rocks at the northern end of the Belhelvie layered intrusion display progressive cryptic variation over a stratigraphic thickness of approximately 800 m in steeply-dipping cumulates, which young from W to E. This variation is shown by olivine (Fo87−77), orthopyroxene (En87−79), clinopyroxene (Ca45Mg48Fe7 to Ca44.5Mg45.5Fe10) and plagioclase (An81−75). The Belhelvie succession is believed to be equivalent to the poorly-exposed and structurally complex Insch Lower Zone. A laterally impersistent hypersthene-gabbro unit within the main sequence is re-interpreted as a downfaulted block of slightly more evolved cumulates. A repeat sequence of peridotites, troctolites and gabbros on the eastern side of the intrusion, and separated from the underlying main succession by a thin septum of country rock, is believed to represent a fresh influx of magma.
Zoned hibonites from Punalur, South India
Authors: Santosh M. , Sandiford M. , Reed S. J. B.
Published: December 2006

Zoned hibonites from a kalsilite, leucite, spinel, corundum, perovskite gneiss from the southern Indian granulite terrain near Punalur, Kerala, have rims that are the most Ti-rich yet recorded (0.83–0.87 Ti atoms per 19 O) and are essentially free of REE elements (ΣREE < 0.01 atoms per 19 O) while the cores are the most REE-rich compositions yet recorded (ΣREE = 0.55–0.65 atoms per 19 O). Within the limits of analytical uncertainty, the compositions of the hibonite can be related to the theoretical end-member CaAl12O19 by the substitutions REE R2+ ⇌ CaAl and R2+R4+ ⇌ Al2 with the REE-rich cores containing in excess of 50% of the REE R2+ Al11O19 end member. Minor substitution of Na for Ca occurs in the rims, while non-stoichiometry in both the cores and rims is indicated by partial 12-fold site occupancy. Ion-microprobe analysis of the REE-rich hibonites reveals strong enrichment in LREE with La/Lu c. 250 000.
The synthesis and composition of georgeite and its reactions to form other secondary copper(II) carbonates
Authors: Pollard A. M. , Thomas R. G. , Williams P. A. , Just J. , Bridge P. J.
Published: December 2006

Comparison of the infrared spectra of georgeite and a phase which can be reproducibily synthesised in the laboratory shows that the mineral is an amorphous analogue of malachite, Cu2CO3(OH)2. Synthetic studies also explain the chemical conditions under which georgeite may form, as well as those which can cause it to react to either malachite or chalconatronite. Parallels may be drawn between the laboratory observations and known mineral associations of georgeite.
Apophyllite and other zeolite-type minerals from the Whin Sill of the northern Pennines
Authors: Young B. , Dyer A. , Hubbard N. , Starkey R. E.
Published: December 2006

Apophyllite, analcite, chabazite, prehnite and stilbite are described from pectolite-, chlorite-, calcite- and quartz-bearing veins and joint coatings in the late Carboniferous quartz dolerite of the Whin Sill of the northern Pennines. These veins represent the final hydrothermal stages in the sill's emplacement and are not related to the widespread lead-zinc-barium-fluorite mineralization of the northern Pennine orefield. Thermogravimetric studies of apophyllites from the two Whin Sill occurrences reveal that at one locality the minreal is fluorapophyllite, at the other hydroxyapophyllite.
Sulphur isotope evidence for the origin of cave evaporites in Ogof y Daren Cilau, south Wales
Authors: Bottrell Simon H.
Published: December 2006

Gypsum evaporites are forming under desiccating conditions in relict cave passages in Mynydd Llangattwg, south Wales. Sulphur isotope compositions of these sulphates indicate that oxidation of diagenetic pyrite in the overlying Millstone Grit is the source of sulphate solutions, rather than dissolution of evaporitic sulphate in the limestones.
The petrochemistry of the Lower Proterozoic metamorphic rocks from the Dabieshan-Lianyungang area, the southeastern margin of the North China Platform
Authors: Longkang Sang
Published: December 2006

Based on geological studies, 141 rock analyses and 5 trace element analyses of metabasites, the present paper deals with the rock association, chemical features, protolith formation and the original tectonic settings upwards through the Lower Proterozoic metamorphic strata in the Dabieshan-Lianyungang area, in the south-east of the North China Platform. The results of the study indicate that the lower and middle parts of the metamorphic strata comprise terrigenous clastics, phosphoritic and aluminous sedimentary formations which formed under stable continental margin conditions. In the middle-upper part a calc-alkaline volcano-sedimentary formation under the active continental margin was developed. The Lower Proterozoic meta-strata of sedimentary-volcanosedimentary origin from bottom upwards suggest that the tectonic evolution of the south-eastern margin of the North China Platform is a process from stabilization to mobilization. This process suggests a northward subduction of the Yangtze Plate under the North China Plate during the later part of the early Proterozoic.
Competitive diffusion-controlled growth of porphyroblasts
Authors: Carlson William D.
Published: December 2006

In a diffusion-controlled process of nucleation and growth, adjacent porphyroblasts compete with one another for nutrients. When the effects of this competition are evaluated quantitatively for garnet porphyroblasts in pelitic rocks from the Picuris Range of New Mexico (U.S.A.), significant correlations arise between crystal sizes and the volumes of the domains from which the crystals drew their nutrients. These correlations strengthen the conclusion drawn from earlier work on spatial dispositions, zoning patterns, and crystal size distributions that the kinetics of intergranular diffusion governed the crystallisation of these porphyroblasts.

Computer simulations indicate that competition for nutrients during diffusion-controlled growth may have small but detectable effects on crystal size frequency distributions. Diffusional competition therefore introduces relatively minor inaccuracies into attempts to extract quantitative information on crystallisation processes from size distributions using models for the growth of isolated porphyroblasts. In contrast, the effects of diffusional competition on patterns of compositional zoning may be substantial, especially for porphyroblasts in rocks for which chemical inhomogeneity of the precursor leads to strongly clustered spatial dispositions. In such rocks, clustering may alter the patterns of compositional zoning in ways that obscure evidence for diffusion-controlled growth.
Coupled substitutions in goldfieldite–tetrahedrite minerals from the Iriki mine, Japan
Authors: Shimizu Masaaki , Stanley Chris J.
Published: December 2006

Chemical compositions of goldfieldite-tetrahedrite series minerals from the Iriki mine in Japan are reported for the frst time. The compositional variations of coexisting goldfieldite [atomic proportion Te > (Sb + As + Bi)], tellurian tetrahedrite [Sb > (Te + As + Bi)], and Te-free tetrahedrite from this locality are considered alongside data from the literature. These show that the substitution of (Sb, As)3+ for Te4+ in natural goldfieldite-tetrahedrite series minerals occurs by the following two mechanisms: (i) tetrahedrite, and goldfieldite, form a continuous solid-solution according to the coupled substitution of Cu+Te4+ for (Cu,Fe,Zn)2+(Sb,As)3+, and (ii) goldfieldite, and the ideal end-member, might also form a continuous solid-solution by the coupled substitution of ☐(vacancy)Te4+ for Cu+(Sb,As)3+. According to this work, the general formulae of tellurian tetrahedrite and goldfieldite are, therefore, respectively, , with x = 0 to 2 and , with y = 0 to 2.
Arsenic-silver incompatibility in fahlore
Authors: Ebel Denton S. , Sack Richard O.
Published: December 2006

Silver-bearing zinc-iron tetrahedrite-tennantite and freibergit fahlores approximating the simplified formula (Ag,Cu)10(Fe,Zn)2(As,Sb)4S13 have been equilibrated with excess electrum (AuxAg1−x) and chalcopyrite + pyrite + iron-bearing sphalerite (CuFeS2 + FeS2 + Fe0.05Zn0.95S) in evacuated silica tubes at 300 °C, in reversed silver-copper exchange experiments with less than 0.1 mg NH4Cl added as a transport medium. A thermodynamic formulation and parameters describing As-Ag incompatibility at 400 °C (Ebel and Sack, 1989), which incorporate large temperature dependencies of standard-state properties and composition-ordering systematics, are shown to apply equally well to these 300 °C results. A generalised graphical model for this mineral assemblage is presented, describing fahlore composition as a function of temperature and the compositions of coexisting electrum and (Fe,Zn)S, which define the Ag(Cu)−1 and Fe(Zn)−1 exchange properties controlling fahlore compositions.
Phase relations of aenigmatite minerals in a syenitic ejectum, wonchi volcano, Ethiopia
Authors: Gaeta Mario , Mottana Annibale
Published: December 2006

Wonchi volcano (Ethiopia) is the second locality for wilkinsonite, the new mineral related to aenigmatite via the coupled substitution 2Fe3+ = TiFe2+. Wilkinsonite occurs as relics surrounded by rims of riebeckite and biotite in a syenitic ejectum which also contains microphenocrysts of aenigmatite. The two minerals do not represent an equilibrium pair. They both formed in the magma chamber under plutonic to hypabyssal conditions, but during two following stages of crystallisation separated by a major drop in ƒO2 conditions.
Petrogenetic implication of the Mössbauer hyperfine parameters of Fe3+-chromites from Sukinda (India) ultramafites
Authors: Mitra Sachinath , Pal Tapan , Pal Taraknath
Published: December 2006

Chromites from two horizons of the Sukinda area (India) marked as ‘grey ore’ and ‘brown ore’ zones have been studied by57Fe Mössbauer spectroscopy, which revealed that both chromite types are oxidised and have a type of disordered spinel structure in which octahedral sites are occupied by Fe2+ions.

The spectra of the grey ore sample can be fitted to three doublets corresponding to Fe2+(A), Fe3+(A) and Fe2+(B) sites. This sample is less oxidised than the brown ore, in which progressive oxidation in the magmatic (?) stage led to the complete conversion of Fe2+inAsites to Fe3+. The spectra of the brown ore are characterised by two doublets correpsonding to two tetrahedral (A) sites of Fe3+with different next-nearest neighbour configurations and a third doublet for Fe2+at theBsite. The brown ores have higher chromium and Fe3+content and have lesser amounts of Ni and Al in comparison to the grey ores. Megascopically, the former shows larger crystal sizes. The high Fe3+content in the brown ore suggests that this type of chromite was formed in a region of highƒO2in the magmatic environment. This perhaps occurred at the part of the mantle where the temperature was higher and the rate of cooling was slower than that of the grey ores which crystallised in the magmatic melt.
Relict clinopyroxenes from within-plate metadolerites of the Petroi Metabasalt, the New England Fold Belt, Australia
Authors: Asthana Deepanker
Published: December 2006

Relict clinopyroxenes from metadolerites of the Early Permian Petroi Metabasalt formation, studied by electron microprobe, show a limited compositional range near the diopside-augite boundary in the pyroxene quadrilateral. Clinopyroxene analyses from three metadolerites, grouped in approximately equal Fs contents, define an overall smooth trend between Fs10 and Fs16. This is typical of clinopyroxenes from mildly alkaline basic magmas. Pyroxene stoichiometry suggests high Fe3+ contents (0.04 to 0.20 a.f.u.), which with high Al (0.10 to 0.31 a.f.u.) and Ti (0.03 to 0.08 a.f.u.) implies that CaTiAl2O6 and CaFe3+AlSiO6 are important ‘other components’. Relative Alz in CaFe3+AlSiO6 decreases and consequently CaTiAl2O6 increases with progressive fractionation. This, with the Fe2+:Fe3+ ratios in the Petroi clinopyroxenes, suggests falling ƒO2 in the magma with fractionation. The ƒO2 controlled entry of Alz, Tiy and Nax into the clinopyroxenes and hence the Petroi clinopyroxene trend.
1966 ash eruption of the carbonatite volcano Oldoinyo Lengai: mineralogy of lapilli and mixing of silicate and carbonate magmas
Authors: Dawson J. B. , Smith J. V. , Steele I. M.
Published: December 2006

Lapilli from the August 1966 eruption of the carbonatite volcano Oldoinyo Lengai consist of carbonate-cemented aggregates of (i) mono- and poly-mineralic fragments of ijolitic rocks, (ii) single grains and clusters of euhedral nepheline, Ti-andradite, and Ti-magnetite, and (iii) corroded pyroxene and wollastonite grains surrounded by coronas containing combeite, melilite, Ca-silicates (possibly larnite and rankinite), and rounded bodies of submicrometre intergrowths with complex bulk compositions dominated by Na,K,Ca-phosphate-carbonate and alkali-iron-sulphide-carbonate. The (ii,iii) materials, together with abundant Na-carbonate, sylvite and fluorite occurring as cement and shells in the lapilli, are attributed to mixing and incomplete reaction of ijolite and carbonatite magmas during the explosive eruption. The rounded submicrometre intergrowths are interpreted as the quench products of two types of immiscible liquids whose properties should be studied by controlled synthesis.
Rare-earth minerals yttrian zirconolite and allanite-(Ce) and associated minerals from Koberg mine, Bergslagen, Sweden
Authors: Zakrzewski M. A. , Lustenhouwer W. J. , Nugteren H. J. , Williams C. T.
Published: December 2006

A study of mine dump material from Koberg, Bergslagen, Sweden has revealed a varied mineral assemblage, including Zr-, REE-, Th- and U-bearing minerals associated with the sulphide ore deposit. Detailed descriptions and microprobe analyses are presented of the rare earth minerals yttrian zirconolite and allanite-(Ce), and the zirconium oxide baddeleyite. Yttrian zirconolite is patchily zoned in the actinide elements Th and U, and the low analytical totals suggest the presence of several weight per cent of H2O. The implications of these features with respect to synthetic zirconolite in SYNROC and to radioactive waste management are briefly discussed. Chemical zoning of individual REE in yttrian zirconolite is described and the REE distribution compared with those of zirconolites from other localities. Allanite-(Ce) is generally unzoned, but contains REE-rich rims which are considered to be sub-micron intergrowths of allanite plus a bastnäisite-type mineral phase. The MgO content of allanite-(Ce) is unusually high and appears to be a characteristic feature of allanite from other cerium and mineral occurrences of Central Sweden. The rare earth minerals at Koberg are interpretated as having been formed as a result of localized remobilization of elements including Ti and Zr with H2O- and CO2-rich fluids.
The geochemistry and cryptic zonation of pyrochlore from San Vicente, Cape Verde Islands
Authors: Hodgson N. A. , Le Bas M. J.
Published: December 2006

Zr-rich pyrochlore crystals in carbonatite from San Vicente (Cape Verdes Islands) show cryptic, concentric and rhythmic chemical zonation with Ca increasing and Ti, U and Zr decreasing towards the rims. In one carbonatite, taken from the Camile dyke, previously undocumented cryptic sector zonation of Ti, U and Zr is also observed in these crystals. The chemical variation is investigated by wavelength-dispersive electron microprobe, with both single spot and crystal map analyses.

The concentric and rhythmic zonation, marked by element substitution, was generated by magma heterogeneity and/or element diffusion kinetics, but it is suggested that the sector zonation, marked by differential site substitution, was governed by protosite variation between octahedral and cubic faces.
Wagnerite with isokite from the Benson Mines, west-central Adirondack Highlands, New York
Authors: Jaffe Howard W. , Hall Leo M. , Evans Howard T.
Published: December 2006

The rare fluophosphate minerals wagnerite, ideally Mg2(PO4)F, and isokite, ideally CaMg(PO4)F, are intimately associated with magnetite-hematite deposits in sillimanite-, garnet-, and pyroxene-rich paragneisses and migmatites at the Benson Mines, near Star Lake in the west-central Adirondack Highlands of New York State. Coarsely crystalline wagnerite occurs in lenticular masses, typically 4 × 8 cm, delineated by sharply cross-cutting, sinuous, 2 cm-wide veins of fine-grained, fibrous to platy isokite and granular fluorapatite. These also penetrate transverse fractures across wagnerite lenses. Isokite formed from the introduction of Ca- and O-rich hydrothermal solutions into wagnerite. Both minerals are monoclinic: wagnerite crystallises in space group P21/a with a = 11.945, b = 12.717, c = 9.70 Å, β = 108.18°, V = 1400.2 Å3, D(calc) = 3.291 g/cm3 for Z = 16; isokite crystallises in space group A2/a with a = 6.909, b = 8.746, c = 6.518 Å, β = 112.20°, V = 364.7 Å3, D(calc) = 3.248 for Z = 4. Optical properties for wagnerite are: α = 1.5845, β = 1.5875, γ = 1.6010, 2V = 51°(calc.) disp = r < v weak, absorption α < β > γ with α = col., β = pale yel., γ = v. pale yel. For isokite only a mean index of refraction, n = 1.598, could be measured. Wet chemical analysis of wagnerite containing a calculated 11.4% of isokite as fine lamellae, gave the formula:
Mineralogy and cryptic layering of the Kunene anorthosite complex of SW Angola and Namibia
Authors: Silva Zenaide C. G.
Published: December 2006

The gabbro-anorthosite complex of SW Angola and Namibia (Kunene Complex) is dominated by anorthosite-troctolite cumulates. Other broadly gabbroic rock types are subordinate. An-rich plagioclase (max. An85) and Fo-rich olivine (max. Fo79) are common in the western area of the complex with plagioclase becoming gradually less anorthitic (min. An45) and olivine less forsteritic (min. Fo62) toward the east. This cryptic change is more pronounced in the northern half of the complex where rocks are darker, fresh, and the rhythmic layering is also more conspicuous. Within the white 'massive' anorthosite type, which is largely restricted to the southern half of the intrusion, cryptic layering is less pronounced. Textures indicate that rocks cooled very slowly and the co-existing mineral compositions indicate re-equilibration to usually low temperatures.
Significance of the cumulate mineralogy of the Belhelvie mafic-ultramafic intrusion—comments on: Silicate mineralogy of the Belhelvie cumulates, NE Scotland, by W. J. Wadsworth
Authors: Boyd R. , Ashcroft W. A.
Published: December 2006

New data on the composition of cumulus phases in the Belhelvie intrusion presented by Wadsworth (1991) are discussed in the light of existing data and of knowledge on the form and internal structure of the intrusion. The relevance of the Rustenburg Layered suite of the Bushveld Complex as a model for the 'single intrusion' hypothesis for the layered basic intrusions in NE Scotland is examined: current knowledge of the Rustenburg Layered Suite and related intrusions suggests that similar crystallisation sequences of cumulus phases and ranges of cryptic variation do not give any case for a single intrusion hypothesis.
Högbomite in sapphirine-bearing rocks from the Bamble Sector, south Norway
Authors: Visser D. , Thijssen P. H. M. , Schumacher J. C.
Published: December 2006

Högbomite is reported from two upper-amphibolite and granulite-facies, sapphirine-bearing, Al–Mg–Fe-rich and silica-poor lens-shaped layers within the Bamble Sector, south Norway. Primary assemblages, indicating peak metamorphic conditions of 773-844°C at 7 kbar (Mg–Fe exchange thermometry), are spinel–sapphirine–biotite–gedrite, spinel–corundum–sapphirine–cordierite and orthopyroxene–biotite–cordierite–plagioclase. Högbomite formed by hydrous alteration and oxidation of primary spinel and rutile and/or ilmenite according to the generalised reaction:

Suggested conditions of högbomite formation are 550–620°C and 6–7 kbar. The högbomites contain 10.2–14.7 wt.% MgO, 04).3 wt.% ZnO, 58.9–62.1 wt.% Al2O3 and 15.6-17.6 wt.% Fe as FeO. The two högbomite may belong to different polytypes, as suggested by their differing TiO2 (9.9-10.1 versus 5.7–5.8 wt. %) and calculated Fe3+ – and H2O–contents. The partitioning of Zn between spinel and högbomite is not uniform and is considered to depend upon prevailing fo2 and aH2O.
Clinotobermorite, Ca5Si6(O,OH)18·5H2O, a new mineral from Fuka, Okayama Prefecture, Japan
Authors: Henmi C. , Kusachi I.
Published: December 2006

Clinotobermorite, Ca5Si6(O,OH)18·5H2O, has been found as a vein-forming mineral in gehlenitespurrite skarns at Fuka, Okayama Prefecture. It is associated with tobermorite, plombierite, apophyllite, and calcite. The clinotobermorite is colourless or white and occurs as tabular or acicular crystals. It is monoclinic with the space group Cc or C2/c. The unit cell dimensions are a 11.331, b 7.353, c 22.67 Å, β 96.59°. Microtwinning and stacking disorder on (001) are observed. On heating the clinotobermorite at 300°C the 002 spacing is reduced from 11.3 to 9.3 Å. Its refractive indices are α 1.575, β 1.580, γ 1.585, and the density 2.58 g/cm3 (meas.), 2.69 g/cm3 (calc). The Moh's hardness is 4.5. Calculation of the analytical data on the basis of six tetrahedral cations shows that this mineral has a simplified chemical formula Ca5.3Si6(O,OH,F)18·5H2O. The chemical composition and the unit cell are closely related to those of tobermorite. It is most likely that clinotobermorite is a low-temperature polymorph of tobermorite.
Transformation of chernikovite into meta-uranocircite II, Ba(UO2)2(PO4)2.6H2O and study of its solubility
Authors: Vochten R. F. , Van Haverbeke L. , Van Springel K.
Published: December 2006

Chernikovite, (H3O)2(UO2)2(PO4)2, was synthesized and subsequently transformed into metauranocircite II, Ba(UO2)2(PO4)2.6H2O, by ion-exchange experiments. The crystals are lemon-yellow and strongly fluorescent. From solubility data a mean pKs value at 25°C was determined as 51.79 ± 0.21. For a cell volume of 16.31.7 Å3 and Z = 4 the density was calculated as 3.970 g/cm3 whereas the measured density is 3.964 g/cm 3. The X-ray powder pattern shows the following strongest lines: 3.609(60)(114), 3.470(60)(123), 2.9272(90)(132)2.9006(90)(312), 2.6065(80)(116), 2.4581(75)(233), 2.2015(100)(143 ; 143), 2.1869(100) (241 ; 226 ;241).
High pressures and the structure of solids of geochemical and geophysical interest
Authors: Goodman C. H. L.
Published: December 2006

Pressures of 10 GPa and above can bring about phase transformations in many oxides, an effect of great interest to geochemists and geophysicists. We can interpret such behaviour as due to the differential compressibility of 'anion' and 'cation' leading to a progressive rise in radius ratio with pressure, and hence, on the classic crystallochemical picture, eventually to an increase in co-ordination number (though with complications which make prediction difficult). More generally, pressure affects Gibbs free energy G directly; for oxides a pressure of 5 GPa gives, very roughly, the same contribution to G as 100°C in temperature (though with opposite sign). Thus high pressure significantly affects the shape and structure of phase diagrams, showing increasingly important effects above, say, 10 GPa—but again prediction can be difficult. However these two complementary approaches to the effects of pressure, helpful though they can be conceptually, are 'crystal-based' and totally neglect another rather littleknown but potentially important effect--the formation of amorphous solids; 'polymers' and glasses. Since amorphous materials are 'non-equilibrium' they are not readily dealt with theoretically; also, since they are difficult to detect by standard crystallographic techniques, they can be overlooked experimentally. The pressure-induced formation of amorphous solids could have significant implications for both geochemistry and geophysics.
The first occurrence of qandilite in Russia
Authors: Oktyabrsky R. A. , Shcheka S. A. , Lennikov A. M. , Afanasyeva T. B.
Published: December 2006

Numerous small octahedra of a black, brittle, magnetic mineral were found in calciphyre and brucite marble, occurring in the northern part of the exocontact zone of the Kondyor ultramafic-alkalic massif (south-eastern part of the Aldan Shield, 250 km north west of sea port Ayan). Their composition corresponds to the group from titanium magnesioferrite (11.53% TiO2) to titanium-rich magnesian spinel (27.34% TiO2), similar to spinellide found in Greenland (Gittins et al., 1982) and in Iraq (Al-Hermezi, 1985) and approved by the Commission on New Minerals as a new mineral named qandilite. Hardness, specific gravity, and reflectance of Kondyor qandilite are similar to those of the Iraq mineral. Peaks of IR-absorption spectra are equal to 580-590 cm−1 (v2) and 431-438 cm−1 (v2). There is a positive correlation between lattice parameters and the amount of Mg2TiO4: from 8.368 Å at 26.6% to 8.429 Å at 60.4%. Kondyor qandilite crystallized together with geikielite, oxidized alumina spinel (8.55% Fe2O3, ftotal : 16.5%), periclase, and forsterite.
Manganese-rich calcic amphiboles of the tremolite-ferro-actinolite series
Authors: Damman A. H. , Lustenhouwer W. J.
Published: December 2006

Amphiboles of the tremolite-ferro-actinolite series from the Bergslagen district in central Sweden have between 0 and 46% of their M1-M3 sites occupied by Mn. These amphiboles are divided into two groups; (1) a group characterised by Mn (M1-M3) > (Mg or Fe) (M1-M3), and (2) a group with much lower contents of Mn (M1-M3), showing the following chemical characteristics: (a) Mn (M1-M3) never exceeds Fe (M1-M3); (b) in Mg-rich members of the group [Mg (M1-M3) > (Mn or Fe) (M1- M3)], the highest amounts of Mn (M1-M3) occur in amphiboles with about 2.20 Mg (M1-M3) per formula unit (pfu); in Fe-rich members of the group Fe [(M1-M3) > (Mg or Mn) (M1-M3)] high amounts of Mn (M1-M3) [> 0.4 Mn (MI-M3)] pfu only occur in amphiboles with >3.40 Fe (M1-M3) pfu; (d) the lowest amounts of Mn (M1-M3) occur in amphiboles with Mg (M1-M3) = Fe (M1-M3).

Mn (M4) increases with increasing amounts of Mn (M1-M3), indicating that solid solution towards the tirodite-dannemorite series is enhanced by incorporation of Mn (M1-M3).
Geochemistry of orbicular diorite from the Grenville Front zone, eastern Labrador
Authors: Victor Owen J.
Published: December 2006

Orbicules in diorite from the Grenville Front zone of eastern Labrador consist of biotite- and/or hornblende-studded, dioritic cores enclosed by fine-grained shell structures alternately enriched and depleted in biotite. The orbicules occur in a mesocratic, quartz-bearing matrix. Epidote of inferred magmatic origin occurs in all parts of the rock. Plagioclase in the matrix is relatively sodic, and biotite more ferroan than in the orbicules, suggesting that the matrix material has the most evolved composition, and crystallized last.

The diorite is unusually aluminous (orbicules: 24.9-27.4 wt.% Al2O3; matrix: 22.4-23.6% Al2O3) and calcic (orbicules: 7.0-8.4 wt.% CaO; matrix: 6.0-6.9% CaO); it shows a positive Eu anomaly, and has elevated Sr concentrations (1800-2500 ppm Sr), demonstrating that, compositionally, it resembles a plagioclase cumulate. Mass-balance calculations suggest that the orbicule cores had a crystal/melt ratio of ≤5. This accounts for the extreme fractionation of the rock (e.g., in orbicules, Zr <5 ppm). Compared with fractional crystallization patterns, variation diagrams show counter-trends (e.g. the siliceous matrix contains elevated TiO2) or scatter for several components, suggesting that the crystal/melt ratio governed some of the geochemical characteristics of the diorite.

The presence of coarse mafic clots containing primary epidote, biotite and/or hornblende testify to an elevated water content in the orbieule cores. The shell magma apparently formed as a result of the interaction of supercooled orbicule core fluids with the matrix magma, and tended to serve as a reservoir for alkalis and Fe. Alkalis and Ca diffused in opposite directions, possibly as a result of a temperature gradient at the orbicule/matrix interface. This, however, requires decoupling of the thermodiffusional behaviour of alkalis and femic components in hydrated intermediate magma, which contrasts with documented Soret diffusion in mafic systems.

The solidification of the shell magma prior, to the orbicule cores and matrix is attributed to dewatering, consistent with the fine grain size of the shell structures. Except where remobilized core material has disrupted the shells, the cores crystallized in isolation from the matrix, which fractionated toward a more evolved composition.
Relation between graphitization of organic matter and clay mineralogy, Silurian black shales in Central Spain
Authors: Barrenechea J. F. , Rodas M. , Arche A.
Published: December 2006

A horizon containing graphite in the Early Silurian slates of the Eastern Central System, Central Spain, has been studied. The carbonaceous slates contain quartz, muscovite, graphitized organic matter, plagioclase, pyrite and apatite; and the slates above the graphite horizon contain quartz, phengite, plagioclase and chlorite. The origin of the graphite is related to a period of very slow accumulation rate, anoxic seafloors deep-water upwellings and plankton blooms. The chlorite and graphite are mutually exclusive and by' using the chlori te AlIV content and the graphite Co parameter, the conditions of metamorphism were calculated to be 300 ± 20°C and 1.5-2 kbar.
Reflected-light microscope and SEM/EMP observations on the behaviour of aurostibite (AuSb2) during amalgamation
Authors: Jedwab Jacques , Chuva Jose Mendes , Poot Eric
Published: December 2006

The Mobale gold mine (Kivu, Zaire) has been worked since 1923, but the presence of aurostibite in the ore was recognized only very recently. The discovery of the mineral has also led to the recognition of its heretofore unsuspected reactivity during the amalgamation ore dressing operations. At the surface of aurostibite a layer of up to 30 μm thickness forms which has an overall brown colour and a low reflectivity, and is composed of several variegated, concentric zones. These zones contain gold, mercury, antimony and oxygen, with traces of iron and arsenic. Oxygen is present with a concentration range of 2-4 wt.% (20-30 at.%). The zones form at the expense of aurostibite, according to micrographical criteria. In complex grains formed of gold-arsenopyrite-galena-aurostibite, only aurostibite is affected by the formation of the external brown zones. Later pure gold veneers are deposited on the outermost surface of the brown layers during the processing of the ore. The newly discovered features of processed aurostibite could explain some of the difficulties met with during the dressing of antirnonian gold ores.