bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium-poor pyroxenes: phase relations in the system CaO MgO-Al2O3-SiO2
Authors: Biggar G. M.
Published: December 2006

Using previously published data and a few new data the compositions of protopyroxene, orthopyroxene, and pigeonite, coexisting with liquid in the system CaO-MgO-SiO2, are reviewed and shown to depend subtly on the number and nature of the coexisting phases such as forsterite, silica, other pyroxene, and liquid. Broadly, protopyroxene contains 0 to 1.0 wt. % CaO, orthopyroxene 1.4 to 2.2%, and pigeonite 3.0 to 6.5%, but pigeonite coexisting with olivine contains up to 1.5 wt. % more CaO than pigeonite coexisting with SiO2 at the same temperature.

In the system CaO-MgO-Al2O3-SiO2 some new analyses and all previously published microprobe analyses of pyroxenes fall into three compositional groups, which are hereafter used to name the pyroxene irrespective of whatever description the original authors gave to their products. For these groups, the compositional subtleties depend on the number and nature of coexisting phases and these are illustrated using sketches of the solid solution polyhedron for each phase, to illustrate, in particular, the decomposition of pigeonite as temperature drops, at 1276°C when forsterite, diopside and liquid coexist, but at other temperatures when other phases coexist. The assemblage orthopyroxene, anorthite, diopside, forsterite is established as the solidus at 1244°C by X-ray diffraction and by new microprobe analyses, and not protopyroxene with anorthite, diopside, and forsterite as was previously accepted. Liquidus surfaces for forsterite and protopyroxene, forsterite and orthopyroxene, and forsterite and pigeonite, are drawn, with temperature data, and several crystallization paths demonstrate the double resorption boundaries, forsterite-protopyroxene-orthopyroxene-liquid and forsterite-orthopyroxene-pigeonite-liquid, and demonstrate crystallization of four pyroxenes, resorption of three of them, and reprecipitation of a second generation of one of them.

No new data are presented for the solidus of the system CaO-MgO-SiO2, but a reinterpretation of the existing data suggests that the solvi of these alumina-free pyroxenes do not show an increase in CaO as temperature decreases. This is contrary to previous interpretations which have mingled data for alumina-bearing and alumina-free pyroxenes. The reinterpretation also favours the reaction protoenstatite + pigeonite ⇌ orthopyroxene at 1375°C and a revision of the previously accepted P-T (Schreinemaker's) net for the pyroxenes is proposed which does not accept orthopyroxene ⇌ protopyroxene + diopside at 1100°C at one bar, which previously has always been accepted by extrapolation from the experimental data at 1 kbar.
Metamorphic differentiation; a mechanism indicated by zoned kyanite crystals in some rocks from the Lukmanier region, Switzerland
Authors: Bramwell M. G.
Published: December 2006

Two samples of garnet-kyanite-staurolite schist from Lukmanier, Switzerland, each contain two chemical varieties of kyanite which occur in texturally distinct areas of the rock. Type 1 form large idiomorphic crystals within an open crenulation cleavage S3. They exhibit a systematic zonation of F2O3, with core values of 0.8% decreasing to 0.3% at the crystal margin. Type 2 form small, much less abundant crystals in areas between S3 cleavage zones, and have a homogeneous distribution of 0.3% Fe2O3 throughout the crystal.

It is suggested that the first-nucleated crystals contain the highest core concentration of Fe2O3 and are the largest. A positive correlation between core Fe2O3 values and crystal size is interpreted as a nucleation and growth sequence. This indicates that the first crystals formed preferentially in S3 (Type 1), with Type 2 crystals growing later outside the S3 zones.

Concentration of kyanite in S3 zones produces a distinct mineral banding in the rock. A mechanism for the development of metamorphic differentiation by preferred nucleation of kyanite in S3 is proposed.
Refinement of the crystal structure of botallackite
Authors: Hawthorne F. C.
Published: December 2006

The crystal structure of botallackite, Cu2(OH)3Cl, monoclinic, a = 5.717(1), b = 6.126(1), c = 5.636(1)Å, β = 93.07(1)°, V = 197.06(5)Å3, space group P21/m, Z = 1, has been refined to an R index of 3.8% for 350 observed (4σ) reflections, measured with Mo-Kα X-radiation on an automatic four-circle diffractometer. The structure consists of sheets of edge-sharing Cuϕ6 (ϕ = unspecified anion) octahedra of composition Cu2(OH)3Cl; these sheets are // {100}, and are joined by hydrogen bonding between oxygen and chlorine anions, thus accounting for the perfect {100} cleavage and the platy habit of botallackite.
The iron content and optic axial angle in zoisites from Galicia, NW Spain
Authors: Maaskant P.
Published: December 2006

Electron probe microanalyses of zoisites from high-grade metamorphic rocks in Galicia, NW Spain have been obtained. The elements Na, Mg, P, K, Ti, and Mn were not detected above the 0.1 wt. % level. Assuming all Fe is present as Fe3+, a clear relation is obtained between the Fe content and the optic axial angle. Zoisite with 1.6 wt. % Fe2O3 proves to be uniaxial at 589 nm; uniaxiality in blue light (470 nm) lies at 1.5 wt. % Fe2O3. A change of the optic sign, from positive to negative, is obtained at 2.9 wt. % Fe2O3. The presence of minor elements greatly affects this relation, as is indicated by analyses of sector-zoned Sr-bearing zoisites of a muscovite-zoisite pegmatite from the same region. Under retrograde conditions Fe-rich α-zoisite reacts to form less Fe-rich α-zoisite or β-zoisite and clinozoisite.
Pseudomesolite is mesolite
Authors: Nawaz Rab , Malone John F. , Din Victor K.
Published: December 2006

Pseudomesolite from Carlton Peak, described by Winchell (1900), is shown to be mesolite by means of chemical and X-ray data. A proposal to this effect has been accepted by the International Mineralogical Association's Commission on New Minerals and Mineral Names. Electron microprobe analysis revealed variations in the composition of pseudomesolite and showed the presence of faroelite. The X-ray powder diffraction pattern is similar to that of mesolite. Single-crystal Weissenberg photographs showed a twinning intergrowth which is explained by a 90° rotation of 50% of the unit cells about the c-axis, so that the a- and b-axes of rotated cells coincide with the b- and a-axes respectively of the unrotated cells. This twinning can not be detected optically. Mesolite has recently been proved to be orthorhombic, contrary to the long-held view that it is monoclinic.

Pseudomesolite from Oregon is also shown to be mesolite by single crystal Weissenberg photographs. A wet chemical analysis shows this material to be extremely silica-rich.
The disposal of radioactive wastes into the marine environment: the presence of hot particles containing Pu and Am in the source term
Authors: Hamilton E. I.
Published: December 2006

Radioactive particulate matter (identified as hot particles) is present in the effluent discharged by the British Nuclear Fuels Ltd (BNFL) uranium reprocessing plant at Sellafield, Cumbria, UK. There is very little information on the abundance or chemical and physical forms of solid matter in the effluent; even less is known of the significance of particulate debris in relation to the uptake of radionuclides for non-occupationally exposed people as a result of transfer along marine foodchains. Some observations on the occurrence and abundance of hot particles in the vicinity of Sellafield are reported, with special reference to those that contain transuranic radionuclides (Pu,Am,Cm). Some of the uncertainties are discussed in an evaluation of the significance of hot particles, albeit aggregates of colloids for the smallest particles, and exposure to man from ionizing radiation. There is no evidence that hot particles derived from BNFL and subsequently dispersed into the marine environment represent a hazard to man. However, further studies are required in order to determine whether or not the pathways followed by the particles are significant, or different to those of other radionuclides through which the radiation exposure of man within this region of Cumbria is assessed.
Hydrothermal crystallization of a radioactive waste storage glass
Authors: Savage David , Robbins Jane E. , Merriman Richard J.
Published: December 2006

A borosilicate glass, containing 25 wt. % of simulated high-level radioactive waste has been reacted with water at 350°C and 500 bars for 14 and 48 days using large-volume ‘cold-seal’ high-pressure equipment. Under these conditions the glass crystallizes a suite of mineral phases including: albite, NaAlSi3O8; aegirine, NaFeSi2O6; riebeckite, Na2Fe2(Fe,Mg)3Si8O22(OH)2; zektzerite, LiNaZrSi6O15; barium-strontium molybdate, (Ba,Sr)MoO4; stillwellite, (Nd,Ce,La)BSiO5; willemite, Zn2SiO4; smectite; a lithium-sodium borosilicate hydrate; melilite (åkermanite), Ca2MgSi2O7. A description of the morphology of these phases is given, together with a number of chemical analyses. The implications of the incorporation of waste species in these mineral phases to the disposal of high-level radioactive waste is discussed.
The use of zeolites for the treatment of radioactive waste
Authors: Dyer A. , Mikhail K. Y.
Published: December 2006

The uptake of 137-Cs and 90-Sr on to synthetic zeolite A has been studied. The use of a combined barium exchange followed by a relatively mild heat treatment has been shown to fix the isotopes within a collapsed zeolite structure. Leaching experiments using deionized and simulated sea and pond waters were carried out on zeolite compacts and zeolite/cement composites. They demonstrated the effectiveness of the calcination and cement containment. Some comments on the interpretation of leach test data are made.
Geological control of fracture permeability in the Carnmenellis granite, Cornwall: implications for radionuclide migration
Authors: Heath M. J.
Published: December 2006

Multi-packer hydraulic tests and radioactive tracer experiments carried out in boreholes in the Carnmenellis granite have shown that the flow of water through the rock is largely confined to narrow zones separated by zones of very low permeability. Correlation of the hydraulic data with geological data from oriented cores has shown that most of the flow is associated with discrete geological features, including pegmatitic and other veins, and elvan (quartz-feldspar porphyry) dykes, characteristic features of the granite of the area. Joints have also been found to conduct water, particularly in the upper 250 m of the granite. The permeability of the granite has been found not to be simply a function of fracture frequency, long sections of highly fractured rock having no associated flow under test conditions. While flow paths have been found to become less frequent with depth, flow rates do not vary over the depths studied, the highest flow rate recorded at the site being associated with a vein at 637 m. Water-conducting fractures have been found to have certain preferred orientations which vary with depth. A set striking 155°C is particularly well developed in the upper 250 m of the granite. This orientation is significant in that it is parallel to the cross-courses in the nearby mineralized belt with which the younger (Tertiary) mineralization tends to be associated and from which thermal brines issue into several local mines. These fractures are also approximately parallel to the maximum horizontal stress which affects the granite and which appears to be responsible for the selective opening of joints of certain orientations.
NaC1 crystallization at the MgCl2/NaC1 solution boundary–a possible natural barrier to the transport of radionuclides
Authors: Sander W. , Herbert H.-J.
Published: December 2006

Concentration, conductivity, temperature, and flow logs from sixteen brine-filled shafts in northern Germany have shown that the brines in all former potash salt mines exhibit a very sharp stratification into lower Mg-rich brine, an upper layer of Na-rich brine, and groundwater at the top. Laboratory experiments have shown that, at the MgCl2-brine/NaCl-brine boundary, both solutions become oversaturated with regard to NaCl, due to diffusion processes. NaCl therefore crystallizes from the solutions and forms a salt plug in the boundary region, which considerably reduces further diffusion. It is concluded that the observed effects would also take place in shafts. The backfilling material helps to nucleate the halite crystals and provides a structure on which they might be supported. The results of these experiments show that the density boundaries in the brine bodies act as barriers against transport of matter while the formation of a halite plug growing independently at the MgCl2/NaCl-brine interface acts as an additional barrier.
A survey of white mica crystallinity and polytypes in pelitic rocks of Snowdonia and Llŷn, North Wales
Authors: Merriman R. J. , Roberts B.
Published: December 2006

Pelitic rocks in North Wales, ranging in age from late Precambrian to Silurian were sampled. XRD analysis was used to determine the mineralogy and white mica crystallinity of separated < 2 µm fractions. Results show that three stages of metapelite recrystallization can be distinguished. Stage I metapelites are uncleaved or feebly cleaved with crystallinities > 0.43Δ°2θ; the 1Md polytype dominates < 2 µm fractions, occurring as K-and Na-micas. Stage II metapelites show variable cleavage development and crystallinities in the range 0.26-0.43Δ°2θ; 1Md and 2M1 polytypes occur and K- and Na-micas are commonly regularly interstratified. Stage III metapelites are strongly cleaved with crystallinities < 0.26Δ°2θ; the 2M1 polytype is dominant, occurring as K-mica and paragonite. Pelites bearing pyrophyllite, rectorite, and corrensite are found close to plug-like intrusions and were contact altered prior to regional metamorphism. 1M mica is common in deeply buried but relatively undeformed volcaniclastic rocks of the Arfon Group.

Contours of equal crystallinity (isocrysts) are plotted with metabasite zones on a metamorphic map. This shows that stage I metapelites are equivalent to the subpumpellyite zone (≡?laumontite zone). Stage II metapelites are equivalent to the prehnite-pumpellyite facies and stage III metapelites to the clinozoisite and biotite zones of the greenschist facies.
Phase equilibria and mixed parageneses of metabasites in lowgrade metamorphism
Authors: Liou J. G. , Maruyama S. , Cho M.
Published: December 2006

The system Na2O-CaO-MgO Al2O3-SiO2-H2O is proposed to model phase equilibria and mineral parageneses for low-temperature metamorphism of basaltic rocks. Univariant reactions marking the transitions between various sub-greenschist facies are identified and some have been experimentally determined. The introduction of Fe2O3 into the model system at fixed FeO/MgO ratio creates continuous reactions for facies boundaries and discontinuous reactions for invariant points of the model system. Both qualitative and quantitative effects on P-T displacement and phase compositions are discussed. The XFe3+ isopleths for epidote were plotted to exemplify the transition from the zeolite through prehnite-pumpellyite to prehnite-actinolite facies. T-XFe3+ relations were established for continuous and discontinuous reactions relating such facies transitions. Because of the common occurrence of two or three Ca-Al hydrosilicates in low-grade metabasites, an isobaric Al-Ca-Fe3+ projection from chlorite may be used to illustrate mineral assemblages and compositions of the coexisting Ca-Al silicates in the presence of quartz, albite, and chlorite. Reported occurrences in several classic burial metamorphic terrains and ocean-floor metabasites in ophiolites are described. Only the composition of a mineral from a buffered assemblage can constrain the intensive properties for metamorphism; previously reported compositional trends for pumpellyite and epidote with increasing metamorphic grade are oversimplified.
Low-grade metamorphism and accretion tectonics: Southern Uplands terrain, Scotland
Authors: Kemp A. E. S. , Oliver G. H. J. , Baldwin J. R.
Published: December 2006

Previous studies of low-grade metamorphism in the Southern Uplands accretionary terrain indicated prehnite-pumpellyite facies/anchizone conditions developed throughout the area, except for local preservation of trench-slope sediments and an accreted seamount at zeolite facies/advanced diagenetic grade. New graptolite reflectance data are presented that show a general northward increase in temperature in the Southern Uplands. The results from two cross-strike traverses in the southern and central belts in contemporaneous sequences, using illite crystallinity, illite lateral spacing (bo) , and graptolite reflectance, indicate the development of systematic accretion-related low-grade metamorphism. Well-developed and constant anchizone conditions occur throughout the NE (Langholm) traverse, associated with common, F1 accretion-related folding and a regionally penetrative S1 cleavage. In the SW (Kirkcudbright) traverse, however, the youngest, last accreted packets are preserved at a transitional diagenetic stage and lack a penetrative S1 cleavage. Illite crystallinity, graptolite reflectance, and bo increase systematically northward through earlier accreted packets, reaching values of the NE traverse only at the northern end. The concomitant increase of bo with illite crystallinity suggests the relatively high P-low T trajectory characteristic of subduction zones. Integration of metamorphic and structural data relates increasing intensity of aceretion-related F1 folding, developmertt of S1 fabric, and onset of later fold phases to grade of metamorphism and structural level within the accretionary pile.
Low-temperature recrystallization of Franciscan greywackes from Pacheco Pass, California
Authors: Maruyama S. , Liou J. G. , Sasakura Y.
Published: December 2006

Low-temperature metamorphism of the Franciscan complex at Pacheco Pass occurs at P-T conditions near the so-called jadeite isograd. Along Highway 152 in the Diablo Range, from west to east, four distinct prograde metamorphic zones are defined: (I) albite-quartz zone, (II) albite-rich, albite-quartz-clinopyroxene assemblage, (III) clinopyroxene-rich, albite-quartz-clinopyroxene assemblage, and (IV) clinopyroxene zone. Metamorphic pyroxenes are restricted to zones II, III, and IV in metagreywackes, but metabasites contain augite-rich pyroxenes even in zone I. With increasing grade, the compositions of pyroxene in metagreywackes change in XJd from nearly 100 in zone II to about 60 in zone III. The diopside component has little effect on the XJd of pyroxene. The apparent change of XJd reflects differences in pressure and temperature rather than in bulk rock composition. In metagreywackes, at the onset of zone II, albite breaks down to form Jd100 according to the reaction Ab = Jd+Qz. With increasing grade, this reaction leads to less jadeitic pyroxene. From zones II to III, a continuous reaction is delineated: Qz+2 pyroxenes (Jd80Ac15Aug5)=pyroxene (Jd60Ac30Aug10) + Ab.

The metamorphic temperatures are estimated to be about 170°C in zones I and II, and about 230°C in zones II and III. The temperature variation recorded in a single rock is probably less than 30°C The pressure estimate depends on the choice of experimental data for the jadeite-albite-quartz curve; it ranges from 4.5 to 8 kbar. A gently folded thermal structure of the Cretaceous subduction zone metamorphism is postulated for this area.
Significance of illite crystallinity and bo values of K-white mica in lowgrade metamorphic rocks, North Hill End Synclinorium, New South Wales, Australia
Authors: Offler R. , Prendergast E.
Published: December 2006

A study of low-grade metamorphism in late Silurian to early Carboniferous rocks in the North Hill End Synclinorium and adjacent anticlinoria has been made by the determination of illite crystallinity and bo values of K-white mica in eighty slates and phyllites. Illite crystallinity values vary from 0.40 Δ°2θ on the Molong Anticlinorium to 0.12 Δ°2θ within the axis of the synclinorium, suggesting anchizonal to epizonal metamorphic conditions. This is in agreement with previous observations on Ca-Al-hydrosilicate assemblages which indicated a change from prehnite-pumpellyite facies in the anticlinoria adjacent to the synclinorium to middle greenschist facies in the axis. Local variations in crystallinity are attributed to variation in ak+ in fluids migrating along cleavage zones.

The mean bo value obtained from the pelites is 9.017 Å (σn = 0.008; n = 80) which is in close agreement with that obtained from part of the adjacent Capertee Anticlinorium ( = 9.019 Å; σn = 0.007; n = 52). However, ‘t’ tests indicate that two bo populations are present in the synclinorium ( = 9.019 and 9.022 Å), with the lower values concentrated in the southern portion of this structure. The two populations are considered to be the result of slightly different metamorphic conditions prevailing during the deformation of the rocks in the synclinorium. A higher geothermal gradient affecting rocks giving the lower bo values is attributed to the presence of granitoids at shallower depths than elsewhere in the synclinorium.
Mineralogical and chemical evolution of white micas and chlorites, from diagenesis to low-grade metamorphism; data from various size fractions of greywackes (Middle Cambrian, Morocco)
Authors: Wybrecht E. , Duplay J. , Piqué A. , Weber F.
Published: December 2006

Four size fractions have been separated and studied in eight samples of Cambrian greywackes, ranging from non-metamorphic to low metamorphic grade. Chemical study included analyses of each size fraction and comparison with the whole rock analysis. Mineralogical study involved analyses of individual crystals using microprobe (> 6 µm) and STEM (< 6 µm). This showed that in each fraction, a progressive homogenization of the mineralogical composition occurred during the development of metamorphism; that chemical transfers especially of Fe-Mg and K-Na, occurred between fine and coarse fractions and that recrystallization in fine and coarse fractions was simultaneous.
Stable isotope compositions of alteration fluids in low-grade Lower Palaeozoic rocks, English Lake District
Authors: Thomas L. J. , Harmon R. S. , Oliver G. J. H.
Published: December 2006

A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the composition of fluids involved in the metamorphism of Lower Palaeozoic rocks in the English Lake District. Three fluid fields have been defined from secondary phases: 1, syn-burial metamorphic D-enriched fluids from epidote and chlorite at a temperature between 250 and 350°C; D-depleted fluid measured from groundmass and quartz inclusions; 3, a mixed magmatic-meteoric fluid with an intermediate H-isotopic composition estimated from W/R granite data and calculated from illite.
Hydrothermal mineralogy of calcareous sandstones from the Colorado River delta in the Cerro Prieto geothermal system, Baja California, Mexico
Authors: Schiffman Peter , Bird Dennis K. , Elders Wilfred A.
Published: December 2006

The Cerro Prieto geothermal system provides a unique opportunity for the detailed study of calc-silicate mineral transitions between the diagenetic clay-carbonate and greenschist facies within the terrigenous sediments of the Colorado River delta. In this system, progressive devolatization reactions within carbonate-cemented, quartzofeldspathic sediment have produced a distinct hydrothermal mineral zonation at temperatures between 200–370°C and fluid pressures below 0.3 kbar. Descriptive and compositional data are presented for these minerals which include wairakite, epidote, prehnite, actinolite, clinopyroxene, garnet, sphene, biotite, microcline, and calcite. Partitioning of octahedral Fe, Mg, and Al between coexisting authigenic silicates is comparable with data from higher temperature metamorphic rocks and demonstrates an approach to local equilibrium within this system. Calculated fugacities of oxygen at temperatures above 300°C are (with rare exception) more reducing than that defined by the quartz-fayalite-magnetite buffer, a result consistent with the scarcity of hematite and grandite and the ubiquitous presence of organic material in Cerro Prieto sandstones.
Pumpellyite-dominated metadomain alteration at Builth Wells, Wales–evidence for a fossil submarine hydrothermal system?
Authors: Bevins R. E.
Published: December 2006

Two metamorphic alteration styles have been observed in basic lavas and volcaniclastic rocks of the Builth Volcanic Series of Ordovician age exposed at Llanelwedd Quarry, in the Builth lnlier, Wales. The first alteration style is characterized by the development of a mineral assemblage comprising albite+chlorite+ sphene+ pumpellyite ± prehnite ± calcite ± white mica, although original textures are largely preserved. This alteration pattern corresponds with that developed in volcanic and volcaniclastic rocks elsewhere in Wales, and which is attributed to the effects of burial. The second alteration style is characterized by the development of metadomains dominated by pumpellyite or, more rarely, prehnite. In the metadomains no original textures are seen in hand specimen. This alteration pattern has, so far, not been observed elsewhere in Wales, and it is here suggested that it might result from a submarine hydrothermal circulation system.
Muscovite breakdown and corundum growth at anomalously low fH2o: a study of contact metamorphism and convective fluid movement around the Omey granite, Connemara, Ireland
Authors: Ferguson Colin C. , Al-Ameen Sanaa I.
Published: December 2006

In the aureole of the late Caledonian Omey granite corundum develops in the Dalradian country rocks in a zone up to 250 m from the granite contact. The distribution of andalusite and K-feldspar in pelites and calcite+wollastonite+grossularite in marbles is consistent with inner-aureole metamorphic conditions of 615±25°C at 2.5±0.25 kbar, and ⋍ 0.85. Corundum develops from the reaction muscovite → corundum + K-feldspar+H2O and first appears over 100 m further from the granite than the assemblage wollastonite + grossularite + anorthite. Experimentally determined equilibria can be satisfied only if for the corundum-producing reaction was less than 0.6 and perhaps as low as 0.4. Corundum always grows within large muscovite crystals;fH2O within the crystal lattice is unrelated to that in the grain-boundary fluid of the surrounding rock.

Although whole-rock oxidation ratios are irregularly distributed within the aureole they are uniformly low in corundum-bearing rocks. Reducing conditions probably resulted from localized flow of H2O-rich fluid away from the granite in a diffuse channelway that contains most of the corundum localities and also a distinctive skarn. Although corundum growth within muscovite is sealed off from the external water vapour conditions, it is suggested that movement of H2O down a thermal gradient (and hence down an fH2O gradient at constant pressure) promotes the escape of (OH)− from the muscovite lattice and so allows the corundum reaction to proceed.
K-Na exchange equilibria between muscovite-paragonite solid solution and hydrothermal chloride solutions
Authors: Pascal M. L. , Roux J.
Published: December 2006

Three ion exchange equilibrium isotherms between muscovite-paragonite solid solution and 2-molal KCl-NaCl aqueous solutions have been studied at (1) 420°C 1 kbar, (2) 420°C, 2 kbar, and (3) 550°C, 2 kbar. The ΔG°(Joules) ± 2σ of the ion exchange reaction are: ΔG° (1) = −17 259±686, ΔG° (2) = −18 268 ± 560, ΔG° (3) = −16018 ± 336. The excess mixing parameters (‘subregular solution’) of the solid solution (at 1 bar) have been calculated:

The corresponding binodal compositions are (muscovite mol fraction): 12–56% at 420 °C, 1 bar and 15–51% at 550 °C 1 bar. The compositions of micas in equilibrium with perthites (high structural state) at 400, 500, 600 °C and 2 kbar are respectively:Xmus= 91, 86, and 82%.

The mixing properties of the solution were estimated using the speciation of two molal chloride solutions calculated from the dissociation constants of NaCl and KCl in aqueous solution. Although NaCl appears to be substantially more dissociated than KCl, the resulting excess free energy of mixing of the hydrothermal (Na,K)Cl solution was found less than 500 J at temperatures above 400 °C and pressures up to 2 kbar.

The difference in Gibbs free energy of formation (from the elements at 25 °C, 1 bar) between NaCl and KCl in two molal aqueous solutions is proposed:
Zirconolite and baddeleyite from metacarbonates of the Oetzstal–Stubai Complex (northern Tyrol, Austria)
Authors: Purtscheller F. , Tessadri R.
Published: December 2006

Zirconolite and baddeleyite from polymetamorphosed metacarbonates of the Oetztal-Stubai complex (northern Tyrol, Austria) are described in terms of their paragenetic relationship and chemical compositions. For the first time an analysis of a chemically zoned niobian zirconolite (high Nb and low Ti in core, low Nb and high Ti at rim) is presented. Genetic possibilities for the origin of the metacarbonates are discussed in the light of zirconolite- and baddeleyite-formation.
The accuracy of X-ray diffraction methods for determining mineral mixtures
Authors: Brime Covadonga
Published: December 2006

An X-ray diffraction method has been successfully applied to the quantitative determination of mineral mixtures. The absorptive properties of the samples and the number of components determine the analytical procedure to be used. The methods described (external standard plus empirical determination of the mass attenuation coefficient) provides an accurate and rapid alternative to the direct measurement of the mass attenuation, Compton diffusion or internal standard methods. The relative accuracy obtained is of the order of 10% at the 0.1% level, independent of the sample composition.
Effects of resolution on the measurement of grain ‘size’
Authors: Dearnley R.
Published: December 2006

Measurements of fine-grained dolerites by optical automatic image analysis are used to illustrate the effects of magnification and resolution on the values obtained for grain ‘size’, grain boundary length, surface area per unit volume, and other parameters. Within the measured range of optical magnifications (× 26 to × 3571) and resolutions (1.20 × 10−3 cm to 8.50 × 10−6 cm), it is found that the values of all grain parameters estimated by chord size analysis vary with magnification. These results are interpreted in terms of the concepts of ‘fractal dimensions’ introduced by Mandelbrot (1967, 1977). For some comparative purposes the fractal relationships may be of little significance as relative changes of size, surface area, and other parameters can be expressed adequately at given magnification(s). But for many studies, for instance in kinetics of grain growth, the actual diameter or surface area per unit volume is an important dimension. The consequences are disconcerting and suggest that it may be difficult in some instances to specify the ‘true’ measurements of various characteristics of fine-grained aggregates.
Niccolite-magnetite mineralization from Upper Teesdale, North Pennines
Authors: Young B. , Styles M. T. , Berridge N. G.
Published: December 2006

Niccolite and other nickel-bearing minerals have been found in magnetite-rich ore at Lady's Rake Mine [NY 8063 3414] in the North Pennines 5.5 km NW of Langdon Beck, Teesdale, Co. Durham. Associated ore minerals include galena, sphalerite, chalcopyrite, pyrite, and pyrrhotite. Similar magnetite-rich ores, in places bearing ugrandite garnets, have been located at two nearby localities, though without nickel minerals. Petrographic study indicates that this unusual assemblage developed in a skarn environment, probably related to the intrusion of the Whin Sill. Field evidence suggests an association with the Teesdale Fault system. Electron microprobe analyses show that Lady's Rake niccolite is near to end-member composition: analyses of other North Pennine niccolites show up to 25 at. % substitution of S and Sb for As.
New data on glaucocerinite
Authors: Raade Gunnar , Elliott C. J. , Din V. K.
Published: December 2006

The strongest lines in the X-ray powder diffraction pattern of type material of glaucocerinite from Laurion (Greece), indexed on a hexagonal pseudocell, are 10.9 (100) (003), 5.45 (90) (006), 3.63 (80) (009), 2.62 (60) (012), 2.46 (60) (015), 2.231 (50) (018), and 1.981 Å (50) (0.1.11). The pseudocell parameters are a 3.0700(8), c 32.65(1) Å. Chemical analysis of topotype material yields the formula [(Zn,Cu)5Al3(OH)16] [(SO4)1.5·9H2O] based on a pyroaurite-like structure. The pseudocell parameters for this sample are a 3.057(3), c 32.52(5) Å. Optical data are 2Vα ⋍ 60°, α 1.540, β 1.554, γ 1.562; D(meas.) = 2.4±0.1 g/cm3, D(calc.) = 2.33 g/cm3. So-called ‘woodwardite’ from Caernarvonshire, Wales, is identified as the Cuanalogue of glaucocerinite. An ‘11 Å mineral’ occurring together with carrboydite in Western Australia is shown to be the Ni-analogue of glaucocerinite. Alleged cotype glaucocerinite from Laurion is related to woodwardite and has the formula [(Zn,Cu)2Al(OH)6][(SO4)0.5 · 3H2O]. This is a cation-ordered pyroaurite-type structure with hexagonal cell parameters a 5.306(2), c 26.77(2) Å. The strongest X-ray powder lines occur at 8.9 (100) (003), 4.47 (90) (006), 2.55 (60) (113), and 2.28 Å (50) (116).
The Tugtutôq older giant dyke complex: mineralogy and geochemistry of an alkali gabbro-augite-syenite-foyaite association in the Gardar Province of South Greenland
Authors: Upton B. G. J. , Stephenson D. , Martin A. R.
Published: December 2006

The Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.

Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicatefO2andTvalues just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.

The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations andREEpatterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.
Radioelement abundance data for some Dalradian rocks from Co. Donegal, Ireland
Authors: O'Connor P. J. , Long C. B.
Published: December 2006

Data for U, Th, and K, determined by epithermal neutron activation methods, are reported for Lower and Middle Dalradian lithologies from Co. Donegal, Ireland. Abundances are identical to rocks with stratigraphical correlation in the Scottish Dalradian and appear not to have been affected by regional metamorphism to biotite and possibly even garnet grade during the Grampian orogenic phase, or later contact metamorphism in the aureole of the Main Donegal pluton. Uraniferous Dalradian lithologies have not been encountered in Donegal. Incorporation of Dalradian rocks, either by assimilation or as extensive raft trains within the Main Donegal granite, is therefore unlikely to have contributed to the development of known pegmatite-hosted U mineralization associated with this late Caledonian pluton.
Pb-Zn and minor U mineralization at Tyndrum, Scotland
Authors: Pattrick Richard A. D.
Published: December 2006

The Tyndrum Pb-Zn mineralization occurs as veins and vein breccias in NE-SW trending fractures associated with the Tyndrum-Glen-Fyne fault. The major minerals are quartz, galena, and sphalerite with minor chalcopyrite and baryte. Tetrahedrite (sometimes silver-and cadmium-rich), pyrargyrite, marcasite, and pyrite occur as small inclusions (< 100 µm) in the galena-rich veins. Sphalerite formed early in the depositional sequence, mainly in breccias, with increasing amounts of galena and chalcopyrite deposited in the later vein stages of mineralization. Uraniferous veins post-date the main Pb-Zn mineralization and contain uraninite, calcite, baryte, galena, sphalerite, chalcopyrite, argentite, chalcocite, tetrahedrite, and safflorite.

Fluid inclusion studies reveal that the mineralizing solutions contained c.20 wt. % equivalent NaCl + KCl, had an Na/K ratio of 3 : 1 and were boiling during mineral precipitation.

The Tyndrum fault controlled the upward flow of the hydrothermal solutions and its intersection with fractures in quartzites favoured the siting of the veins. The depositional sequence is explained by an increase in temperature during the mineralizing episode. The uraniferous veins may be a late oxidized stage of the main Pb-Zn mineralization.
The rates of dissolution of olivine, plagioclase, and quartz in a basalt melt
Authors: Donaldson Colin H.
Published: December 2006

The dissolution rates of spheres of two magnesian olivines, two plagioclases, and quartz in tholeiitic basalt have been determined at three super-liquidus temperatures and one-atmosphere pressure. There are considerable differences in the rates among the minerals, e.g. at 1210°, 12° above the liquidus temperature of the basalt, labradorite dissolves at 86 µm/h. and the magnesian olivines at 9 and 14 µm/h. The rates are not time dependent and this, coupled with the existence of concentration gradients in the composition of quenched melt adjacent to partially dissolved crystals, indicates that the dissolution rates are dictated by a combination of diffusion and convection of components to and from the crystal-liquid interface. Values for the activation enthalpy of dissolution are small for quartz and plagioclase (40–50 kcal mol−1) but large for olivine 73–118 kcal mol−1). Dissolution of plagioclase in rock melts seems to be a much more rapid process than crystal growth, whereas olivines apparently dissolve and grow at similar rates. Crystal dissolution is sufficiently slow that ascending, crystal-bearing magma may become superheated and yet fail to dissolve the crystal fraction before quenching; this may be the reason that olivine phenocrysts are often rounded.
Potassium pargasite from Einstödingen, Lützow-Holm Bay, East Antarctica
Authors: Matsubara S. , Motoyosh Y.
Published: December 2006

Potassium pargasite containing 3.19 wt. % K2O was found in a skarn from the islet of Einstödingen, Lützow-Holm Bay, East Antarctica, together with some high potassium pargasitic amphiboles. A positive correlation is shown between Fe2+/(Mg+Fe2+) and K/(K + Na(A)) ratios in pargasitic amphiboles suggesting that the increase of Fe2+ serve to stabilize high-K pargasites under the metamorphic conditions of the granulite facies.
Hydroxyl-bastnaesite-(Nd), a new mineral from Montenegro, Yugoslavia
Authors: Maksimović Zoran , Pantó György
Published: December 2006

Hydroxyl-bastnaesite-(Nd), the Nd- and OH-dominant new member of the bastnaesite group, has been found in the red karstic bauxites near Nikšić, Montenegro. It occurs as whitish, irregular aggregates of crystals usually 100–200 µm in diameter. Hexagonal with the cell dimensions a = 7.191 and c = 9.921 Å, with Z = 6. The strongest lines of the X-ray powder diffraction pattern (d, I, hkl) are: 4.95 80(002); 3.596 79(110); 2.911 100(112); 2.077 29(300); 2.042 51(114); 1.914 30(302). The mineral is uniaxial positive, ω 1.715, ɛ 1.81; Dcalc 4.89 g/cm3.

Electron probe analysis, using garnet, apatite and synthetic glass standards, combined with thermogravimetric and evolved gas analysis, gave Y2O3 0.2, La2O3 27.1, Ce2O3 0.3, Pr2O3 8.5, Nd2O3 31.5, Sm2O3 4.4, Eu2O3 1.3, Gd2O3 1.4, CaO 0.3, F 3.3, H2O 2.26, CO2 20.63, sum 101.19, less O = F 1.39, total 99.80%. This analysis calculates to (Nd0.41La0.36Pr0.11Sm0.06Gd0.02 Eu0.02Ca0.01)Σ0.99(CO3)1.03[(OH)0.55F0.38]Σ0.93, or ideally, (Nd,La)CO3(OH,F), with Nd > La and OH > F.
Tourmalinization in the Skiddaw Group around Crummock Water, English Lake District
Authors: Fortey N. J. , Cooper D. C.
Published: December 2006

Veins of tourmalinite were formed by wallrock alteration adjacent to steep fractures in bleached, indurated Skiddaw Group metasedimentary rocks around Crummock Water, north-west Lake District. The vein rock is a fine-grained granoblastic mosaic of tourmaline, quartz, and minor rutile in which bedding is preserved. Brecciation, in which tourmalinite fragments are set in a coarser quartz-tourmaline matrix, is present in some veins. Networks of cross-cutting quartz veinlets with tourmaline, chlorite, and muscovite are very common. The tourmaline is intermediate schorl dravite and mostly brown in plane polarized light, though prisms in breccia matrix and veinlets have blue, low-Ti cores and brown rims. Comparison of tourmalinite and host-rock analyses indicates almost complete loss during tourmalinization of K, Rb, Li, Ba, As, and La, plus depletion in Ce, Y, Na, Sr, P, and Mn. The elements Si, B, Mo, and erratically, minor F, W, and Sn were introduced. Cu, Pb, Zn, and Ca show both gains and losses probably due to initial depletion and subsequent local enrichment. Reduction in Al, Zr, and Ti concentrations relates to dilution by introduced silica. The tourmalinite veins were formed by the action of hydrothermal fluids derived from the concealed late-Caledonian granitic intrusion responsible for the thermal metamorphism of the country rocks.
Stability relations of malachite and azurite
Authors: Vink B. W.
Published: December 2006

Stability relations of malachite and azurite are calculated and shown in Eh-pH diagrams, using ΔF (Gibbs free energy) values listed in Garrels and Christ (1965). The malachite/azurite transition is very sensitive to small chemical changes in the environment: equilibrium is reached at PCO2 = 10−3.45 atm., i.e. close to normal values, whereas the precipitation of both minerals from cupric-ion-bearing solutions takes place at pH values between 6 and 8, depending CO2 partial pressures. It is shown that stability relations of these minerals can be better explained in terms of activities of the carbonate and bicarbonate ion.

Azurite can be formed only under relatively acid conditions at relatively high carbonate activities. Since the latter imply mostly basic conditions, this explains why malachite is the more common form of copper carbonate and that azurite can be formed only under rather unusual conditions. It also explains the frequent alteration of azurite into malachite, due to small changes in carbonate/bicarbonate activities. These alterations include pseudomorphs of malachite after azurite.
Zinc-manganese carbonates from Broken Hill, New South Wales
Authors: Birch W. D.
Published: December 2006

Specimens of honey-brown to pinkish-brown globular carbonates encrusting concretionary goethite–coronadite from the oxidized zone at Broken Hill, New South Wales, have compositions in the rhodochrosite–smithsonite series. This may be the first extensive natural occurrence of this solid-solution series. Growth of the carbonates occurred in zones which have near uniform composition. The ratio MnCO3/(MnCO3 + ZnCO3) for each zone bears a linear relationship to the measured d spacing for the 104 X-ray reflections. Because cerussite is the only other mineral associated with the Zn-Mn carbonates and because of an absence of detailed locality information, the paragenetic significance of these minerals cannot be determined. The solutions depositing them may have been derived from the near-surface equivalents of the Zinc Lode horizons.
The mafic mineralogy of the peralkaline syenites and granites of the Mulanje complex, Malawi
Authors: Platt R. Garth , Woolley Alan R.
Published: December 2006

Studies of the mafic mineralogy of the Mulanje granite-quartz-syenite-syenite Massif of southern Malawi delineate two mineralogically distinct complexes—the Main complex and the Chambe complex. Each complex is associated with its own trend of pyroxene evolution. The Main complex pyroxenes exhibit initial enrichment in hedenbergite before subsequent enrichment in acmite (i.e. sodic-salite-sodic-hedenbergite-aegirine-hedenbergite-aegirine), whereas the Chambe pyroxenes display constantly increasing acmite content with no significant enrichment in hedenbergite (i.e. sodic-salite-aegirine-augite-aegirine). This phenomenon is also reflected in the more Mg-rich amphiboles and biotites of the Chambe rocks when compared to those of the Main complex.

The general evolutionary trend of the Main complex amphiboles is katophorite → ferroricherite → arfvedsonite which broadly correlates with a change in rock type from syenite to granite. Superimposed on this trend is an essentially similar, yet less extensive trend of the more Mg-rich Chambe amphiboles. The micas of both complexes show a general evolution to more iron-rich compositions with relatively constant Al content. Those of the Main complex, however, display extreme iron enrichment with ultimate formation of essentially pure ferrous annite.

Aenigmatite, astrophyllite, fayalite, chevkinite, yttrofluorite, and unidentified RE minerals are characteristic of the Main complex rocks but totally absent from those of the Chambe complex. Ilmenite constitutes the only iron oxide phase in the Main complex rocks whereas titaniferous magnetite (now unmixed) and ilmenite are both present in the rocks of Chambe.

The differences between the two complexes are explained in terms of oxygen fugacity, silica activity, crystallization interval, and the relative rates of development of peralkalinity. In essence, the Chambe magmas are considered to have crystallized under high fO2 conditions with an earlier development of peralkaline tendencies when compared to those of the Main complex magmas. Moreover, a lower initial silica activity, a smaller alkali to alumina ratio, and a correspondingly smaller crystallization interval could account for the lack of highly evolved granitic magmas in the Chambe complex, whereas such magmas are integral in the evolution of the Main complex.