bluuebunny/crossref_metadata_2025 huggingface dataset:
The conversion of smectite to illite during diagenesis: evidence from some illitic clays from bentonites and sandstones
Authors: Nadeau P. H. , Wilson M. J. , McHardy W. J. , Tait J. M.
Published: December 2006

Diagenetic illitic clays from seven North American bentonites of Ordovician, Devonian, and Cretaceous ages and from three subsurface North Sea sandstones of Permian and Jurassic ages have been examined by X-ray diffraction (XRD) and transmission and scanning electron microscopy (TEM and SEM). XRD indicates that the clays from the bentonites are randomly and regularly interstratified illite/smectites (I/S) with 30–90% illite layers, whereas the clays from the Jurassic and Permian sandstones are regularly interstratified I/S, with 80–90% illite layers, and illite respectively. TEM of shadowed materials shows that randomly interstratified I/S consists primarily of mixtures of elementary smectite and ‘illite’ particles (10 and 20Å thick respectively) and that regularly interstratified I/S and illite consist mainly of ‘illite’ particles 20–50 Å thick and > 50 Å thick respectively. Regularly interstratified I/S from bentonites and sandstones are similar with regard to XRD character and particle thickness distribution. These observations can be rationalized if the interstratified XRD character arises from an interparticle diffraction effect, where the smectite interlayers perceived by XRD, result from adsorption of exchangeable cations and water or organic molecules at the interfaces of particles generally < 50Å thick. A neoformation mechanism is proposed by which smectite is converted to illite with increasing depth of burial in sedimentary rocks, based on dissolution of smectite particles and the precipitation/growth of ‘illite’ particles occurring within a population of thin phyllosilicate crystals.
The geochemistry of carbonate cements in the Avalon Sand, Grand Banks of Newfoundland
Authors: Hutcheon Ian , Nahnybida Cynthia , Krouse H. R.
Published: December 2006

Calcite cements from the Lower Cretaceous Avalon zone of the Hibernia field are, in places, extensively recrystallized, which complicates interpretation of the chemical and isotopic data. The oxygen isotopic data are widely scattered with δ18O ranging between +1.6 and −9.2 for calcite and siderite. Siderite has lower δ13C values (−6.6 to −13.2) than calcite +12.4 to −9.8. Typical trace element contents determined by ICP on acid-leached samples, range from 270 to 2100 ppm Sr and 180 to 2200 ppm Zn in calcite.

The trace element data indicate that some of the calcite has been precipitated from, or recrystallized by meteoric water. The trace elements show trends related to variations in δ18O in such a way as to imply that not all the spread to low δ18O values can be attributed to meteoric water influence alone. The data are not well enough constrained to calculate meaningful temperatures, but the range of °18O values probably represents an elevated range of temperatures of precipitation or recrystallization.

Microprobe analyses show that non-recrystallized fossils have a composition distinctly different from veins, cements, and recrystallized fossils, all of which are similar. The compositions of calcite cements are highly variable, with FeO (for example) ranging from 0.15 to 4.39 wt. %, but show no consistent patterns of zonation. Fossil fragments which show no textural evidence of recrystallization have low FeO contents (0.2 wt. %). Meteoric water, believed to be responsible for at least some of the cementation and recrystallization observed, probably entered the Avalon during and after formation of the mid-Cretaceous unconformity.
Multi-component origin of Caledonian lamprophyres of northern England
Authors: Macdonald R. , Thorpe R. S. , Gaskarth J. W. , Grindrod A. R.
Published: December 2006

Mafic lamprophyre dykes in northern England were emplaced soon after the final closure of the Iapetus Ocean at the end of the Caledonian orogeny. High Mg/(Mg+Fe) ratios and Cr and Ni contents are consistent with equilibrium with mantle peridotite. Incompatible trace element abundances suggest that the mantle sources were metasomatized prior to the melting events. Three components are recognized in the lamprophyre chemistry: (i) a depleted mantle source, taken to be that overlying the subducting lithosphere; (ii) a H2O-rich subduction zone component, related to the dehydration of the subducting oceanic crust; and (iii) a CO2-rich phase thought to result from the degassing of the mantle after ocean closure. This multi-component origin may be applicable to other lamprophyres of calc-alkaline affinity.
The distribution of the rare earth elements within the Carnmenellis pluton, Cornwall
Authors: Jefferies N. L.
Published: December 2006

The Carnmenellis pluton is a post-orogenic granite of Hercynian age, comprised largely of porphyritic biotite granites which possess LREE enriched patterns with slight negative Eu anomalies. Electron microprobe and ICP spectrometry data are presented for monazite, which occurs as an accessory mineral in all granite types, and it is demonstrated that this mineral is the principal host for LREE in the biotite granites. HREE are strongly partitioned into the accessory minerals xenotime, apatite, and zircon; only Eu substitutes significantly into the essential minerals. The behaviour of the REE during granite differentiation is controlled by the behaviour of the radioactive accessory minerals, which limits the usefulness of these elements in the petrogenetic modelling of granitic rocks.
Ganomalite from Franklin, New Jersey, and Jakobsberg, Sweden: new chemical and crystallographic data
Authors: Dunn Pete J. , Peacor Donald R. , Valley John W. , Randall Charles A.
Published: December 2006

Chemical analyses for ganomalite from Franklin, New Jersey, and Jakobsberg, Nordmark, Sweden, imply that Mn is an essential element and that the formula is Pb9Ca5MnSi9O33, with Z = 1 for the hexagonal unit cell. Preliminary crystal structure data confirm that Mn and Ca are ordered, as implied by the chemical analyses. Ganomalite is hexagonal, space group P3, with a = 9.82 and c = 10.13 Å. Occurrences of samples from both localities are described, together with analytical data for macedonite from Jakobsberg.
The nature and paragenesis of natural bredigite and associated minerals from Carneal and Scawt Hill, Co. Antrim
Authors: Sabine P. A. , Styles M. T. , Young B. R.
Published: December 2006

Bredigite is a constituent of the very high-temperature, low-pressure, exomorphic suite of Carneal, Co. Antrim. Although this mineral is very rare in nature, it is an important constituent of some slags and cement clinkers but there has been much controversy about its nature, most of the evidence having come from artificial materials. Chemical analysis of the Carneal mineral shows it to be remarkably similar to that from the type locality, Scawt Hill (also analysed here), and that it is an individual mineral species of generalized ionic composition (Ca,Na)14(Mg,Fe2+Fe3+Mn)2(Si,P)8O32. Ba (abundant in the original analysis of the slag mineral) is not a constituent. Accurate X-ray powder data of the natural mineral are given. Bredigite is not Ca2SiO4, nor is it part of a solid solution of variable composition between larnite and merwinite. Analyses are presented for the associated minerals larnite (allowing appraisal of its composition), spurrite, and spinels. The paragenesis is discussed.
Cordierite in the peraluminous granites of the Meguma Zone, Nova Scotia, Canada
Authors: Maillet Lynne A. , Barrie Clarke D.
Published: December 2006

The peraluminous granitoid intrusions of southern Nova Scotia contain several mineralogical expressions of the excess alumina, including variable amounts of cordierite, in different textural types of granitoids, ranging from fine-grained aplites through coarser grained monzogranites and granodiorites, to very coarse-grained pegmatites. A detailed study of the spatial, textural and chemical characteristics of these cordierites suggests that the majority are of relict metamorphic origin, but that primary magmatic cordierites, as well as cordierites which grew in equilibrium with a water-rich fluid phase, also occur.
The lead silicates from Franklin, New Jersey: occurrence and composition
Authors: Dunn Pete J.
Published: December 2006

The lead silicate minerals from Franklin, New Jersey, occurred in two separate assemblages. One of these is characterized by esperite associated with hardystonite and occasional larsenite. The second assemblage can be considered as two parts: one consists of margarosanite, barysilite, nasonite, and ganomalite; the other contains roeblingite and hancockite, together with a number of highly hydrated phases. Chemical analyses indicate that these species conform to their theoretical compositions. There are no simple lead silicates at Franklin; all are compound silicates of Pb with Mn, Zn, and Ca.
Qandilite, a new spinel end-member, Mg2TiO4, from the Qala-Dizeh region, NE Iraq
Authors: Al-Hermezi H. M.
Published: December 2006

Qandilite, a new species of the spinel group, has been found in a forsterite-rich rock in contact with a kaersutite-rich banded diorite from the Qala-Dizeh region, NE Iraq. Chemical analysis yielded MgO 29.62, FeO 10.32, MnO 0.76, Fe2O3 28.27, Al2O3 4.83, TiO2 26.41, SiO2 0.02, sum 100.23 wt. %. This analysis calculates to [(Mg1.20Ti0.60)][Mg0.12Mn0.02)(Al0.17)]O4 with a composition of Mg2TiO4 63.8, MgFe2O4 12.8, FeFe2O4 23.4 mole %. Qandilite is cubic with a = 8.4033±0014 Å; cell volume 593.40 Å3 and space group Fd3m; Z = 8. The seven strongest lines in the X-ray diffraction pattern are (d,I,hkl): 2.971, 30, (220); 2.53, 100, (311); 2.101, 45, (400); 1.617, 50, (333, 511); 1.486, 60, (440); 1.0938, 30, (553, 731); 0.9704, 25, (555, 751). The colour is black, lustre metallic, streak black, fracture even and the cleavage perfect on (111). It is opaque, strongly magnetic, Dcalc = 4.04, Dmeas = 4.03, and VHN100 = 960–1045 kg/mm2, with H-7. The reflection colour is grey with a pinkish tint; it is isotopic with no internal reflections. Reflectance measurement data in air and oil in the range (400–700 nm) are given. Colour values for illuminant C in air and oil in terms of CIE colour space are: x = 0.307, 0.307; y = 0.311, 0.310; Y% = 13.10, 3.0; λd = 465, 460; and Pe% = 2.0, 2.2. Calculated data for the absorption coefficients (k) and refractive indices (n) in the range 400–700 nm are also presented.
Experimental determination of melting relationships of beryl in the system BeO-Al2O3-SiO2-H2O between 10 and 25 kbar
Authors: Cemič L. , Langer K. , Franz G.
Published: December 2006

The onset of melting of beryl + H2O was determined experimentally in the P-T range 10–25 kbar, 900 to 1200°C, by synthesis runs on the composition Al2Be3Si6O18. Beryl begins to melt incongruently to chrysoberyl, phenakite, and melt at temperatures slightly above 1000°C. At higher temperatures a divariant stability field exists where beryl, chrysoberyl, phenakite, and melt coexist due to the solubility of H2O in beryl and in the melt. The final disappearance of beryl was bracketed between 1050 and 1100°C at 10 kbar and at 1100°C between 10 and 20 kbar. The phases (analysed for Al and Si by electron microprobe) do not show major deviation from stoichiometric composition.
Composition and structural state of coexisting feldspars, Salton Sea geothermal field
Authors: McDowell S. Douglas
Published: December 2006

Active metamorphism of fine grained sandstone in the c.16000 year old Salton Sea geothermal system has produced a suite of chemically equilibrated coexisting authigenic alkali feldspars and re-equilibrated detrital feldspars in the 250–360°C temperature range. At c.335°C the average compositions, 2 Vs, and (t1o+t1m) and Z ordering parameters of coexisting authigenic feldspars are [Or0.52Ab97.40An2.08, 2Vx = 91.3±4.8, (t1o + t1m) = 0.89±0.05, Z = 0.79±0.09], and [Or94.42 Ab5.10An0.48, 2Vx = 70, (t1o + t1m) = 0.90, Z = 0.81]. At c.360°C authigenic albite becomes more An-rich and less ordered [Or1.21Ab92.83An5.97, 2Vx = 87.5±3.4, (t1o + t1m) = 0.85±0.03, Z = 0.70±0.07] and K-feldspar is no longer stable. Detrital plagioclase (An up to 40%) is preserved metastably to temperatures up to c.190°C in strongly carbonate-cemented sandstone which forms part of a geothermally produced permeability cap. It undergoes rapid alkali exchange at temperatures near 200°C, and by 250°C no plagioclase with An-content over 12% is observed. At > 250°C authigenic and most detrital alkali feldspar compositions are in excellent agreement with the Bachinski and Muller (1971) microcline-low-albite solvus.
Conditions of formation of the iron-containing minerals, Hällefors silver mines, Bergslagen, Sweden
Authors: Jasiński A. W.
Published: December 2006

The Hällefors silver deposit is regarded as a volcanogenic-exhalative iron ore deposit with dispersed amounts of Ag-Pb-Zn (±Cu) which has undergone secondary remobilization leading to the concentration of sulphides and sulphosalts. Based on data from the iron oxides and sulphides, the sulphide-sulphosalt mineralization is believed to have been formed in two stages. The first is characterized by the ranges 573-473 K and 2.25–1.5 kbar, higher gradient of changes of logaS2with temperature and mostly sulphide precipitation; the second by the ranges 473–443 K, lower gradient of changes of logaS2and mainly sulphosalt deposition. Assuming the precipitation was from fluids and aqueous solutions, possible conditions of formation of some of the iron minerals have been determined.
Chenite, Pb4Cu(SO4)2(OH)6, a new mineral, from Leadhills, Scotland
Authors: Paar W. H. , Mereiter Kurt , Braithwaite R. S. W. , Keller Paul , Dunn P. J.
Published: December 2006

Chenite, a new lead-copper secondary mineral, has been found on specimens from the Leadhills area, Scotland. It is associated with caledonite, linarite, leadhillite, susannite, and other species, on oxidized galena with chalcopyrite. Electron microprobe analysis yielded PbO 74.5, CuO 7.8, SO3 13.3, H2O 4.4 (by difference), sum = 100 wt. %. The empirical formula (based on 14 oxygens) is Pb3.98Cu1.17S1.98O14H5.82; the ideal formula is Pb4Cu(SO4)2(OH)6, which requires PbO 75.2, CuO 6.7, SO3 13.5, H2O 4.6, sum = 100 wt. %.

Infra-red spectroscopy showed the presence of only and OH− ions, with no H2O.

Chenite is triclinic, P1 or P̄, with a = 5.791(1), b = 7.940(1), c = 7.976(1) Å, α = 112.02(1), β = 97.73(1), γ = 100.45(1)°, V = 326.0 Å3, Z = 1. The strongest lines in the X-ray powder diffraction pattern (d, I/Io, hkl) are: 5.55, 7, 100; 4.32, 6, 11; 3.60, 10 002; 3.41, 9, 10; 3.30, 5, 02; 3.00, 5, 111; 2.80, 7, 12; 2.07, 6, 211/21/13; 1.778, 5, 3/23.

Chenite forms minute, singly terminated, transparent to translucent sky-blue crystals from 0.1 to over 1 mm long, elongated approximately [032]. Twenty different forms (pinacoids) have been identified on the four crystals studied. A good cleavage on {100}, and traces of a second on {001}, can be observed. Optically, chenite is biaxial negative, 2 V(measured) = 67±1°, 2 V(calc.) = 68° (Na). The refractive indices are α 1.871±0.005, β 1.909±0.005, γ 1.927±0.005 (Na). Dispersion is strong, r≫v. The mineral is weakly pleochroic. H (Mohs) ∼ 2½. D = 5.98, and calculated Dx = 6.044 g cm−3.
The chemistry and mineralogy of some granulated and pelletized blastfurnace slags
Authors: Scott P. W. , Critchley S. R. , Wilkinson F. C. F.
Published: December 2006

Samples of granulated slag from Scunthorpe, Humberside, collected over several years, vary somewhat in chemical composition reflecting differences in iron-making practice. All contain some melilite and oldhamite crystals and minor amounts of iron along with the glass. Granulated slag from Usinor, Dunkirk, France, has a little more CaO than the Scunthorpe material with crystals of merwinite and oldhamite. Pelletised slag from Redcar, Teeside, is much more vescicular than the granulated material and contains melilite and oldhamite.

The melilite crystals contain many inclusions of oldhamite and iron. They span a wide range within the akermanite-gehlenite series and are non-stoichiometric in composition. The merwinite may have formed largely by quench crystallization. Oldhamite is probably the first phase to form in all the slags. The silicate mineralogy can be explained in terms of the phase relationships within the CaO-SiO2-Al2O3-MgO quaternary system. The small difference in composition of the French slags is sufficient for them to fall into the primary phase field of merwinite rather than melilite. Assuming that only a minor proportion of crystals is acceptable in slags for use in Portland Blastfurnace Cement, the present low Al (< 11 % Al2O3) British and French slags are approaching an optimum composition.
A model for polysomatism
Authors: Price Geoffrey D. , Yeomans Julia
Published: December 2006

We show that the structures and phases developed in a variety of polysomatic series, including the biopyroboles, are similar to those predicted by a simple spin model—the Axial Next-Nearest-Neighbour Ising (ANNNI) model in a magnetic field. We argue that the different polysomatic structures can be considered as thermodynamically stable phases, composed of ordered sequences of chemically distinct structural modules. We suggest that the key factors which determine the stability of polysomatic phases are (a) the chemical potential, which controls the proportion of the different structural modules, and (b) the competing interactions between first and second neighbour modules within the structures.
Sodic amphiboles in fenites from the Loe Shilman carbonatite complex, NW Pakistan
Authors: Mian I. , Le Bas M. J.
Published: December 2006

The carbonatites at Loe Shilman, near Khyber in NW Pakistan, fenitize their country rocks to form a metasomatic zone c.100 m wide of alternate dark blue (mafic) and pale grey (felsic) banded fenites which grade into unfenitized bedded slates and phyllites. The Na-amphiboles in the banded fenites form a complete solid solution series between magnesio-arfvedsonite and magnesio-riebeckite which coexist with varying proportions of aegirine, albite, and K-feldspar, with or without phlogopite or biotite.

The amphiboles show a gradual decrease in Na2O, K2O, Mg ratio [100Mg/(Mg + FeT + Mn)] and iron oxidation ratio, and an increase in total iron away from the carbonatite contact. The pleochroism correlates with the chemistry and distance from the carbonatite contact.

The Mg ratio decreases from 74 to 35 away from the carbonatite contact. The iron oxidation ratio [100Fe3+/ (Fe3+ + Fe2+)] decreases in the magnesio-arfvedsonite for the first 30 metres from the carbonatite contact, and then increases in the magnesio-riebeckite from 40 to 60 metres from the carbonatite contact. K relative to Na decreases away from the contact in the amphibole, and the decrease in K causes an increase in vacancy in the A site. The main variation in the chemistry in this solid solution series is due to (K,Na)A+(Mg,Fe2+)c ⇌ □ + (Fe3+)c substitution.
Muscovite solid solutions in the system K2O-MgO-FeO-Al2O3-SiO2-H2O: an experimental study at 2 kbarPH2Oand comparison with natural Li-Free white micas
Authors: Monier Gilles , Robert Jean-Louis
Published: December 2006

This paper presents the results of an experimental study of muscovite solid solutions in the system K2O-M2+O-Al2O3-SiO2-H2O-(HF), withM2+= Mg2+or Fe2+in the temperature range 300-700°C under 2 kbarPH2O. Muscovite solid solutions can be described, in this system, as the result of two substitutions. One is the phengitic substitution (x), which preserves the pure dioctahedral character of the mica; the second is the biotitic substitution (y), which leads to trioctahedral micas and does not change the composition of the tetrahedral layer Si3Al. The general formula of muscovite in this system is K(Al2−x−2y∕3M2+x+y□1−y∕3)(Si3+xAl1−x)O10(OH,F)2. Both substitutionsxandyare more extensive at lower temperatures. The extent of solid solution decreases drastically with increasing temperature.

ForT> 600°C, the phengitic substitution (x) becomes negligible, but some biotitic substitution (y) persists. This unsymmetrical decrease of the solid solution of muscovite with increasing temperature is similar to that previously observed in phlogopite, the micas with a tetrahedral layer composition of Si3Al being the most stable. The behaviour of muscovite solid solutions in the ferrous system is qualitatively identical to that observed in the magnesian one, but the extent of solid solution is smaller than with Mg2+. Fluorine neither changes the size nor the shape of the solid solution fields but increases their stability by about 50°C.

A comparison of these experimental results with data on natural muscovites is presented. Most natural primary (magmatic) granitic muscovites lie very close to the muscovite end member, in agreement with their high-temperature origin. Low-temperature muscovites (300–400°C), typically muscovites from hydrothermally altered granitic rocks, can have highxandyvalues. The rate of the biotitic substitutionycan reach 0.6, which corresponds to an octahedral occupancy of 2.2 atoms per formula unit (based on 11 oxygens), consistent with the experimental data.
Obradovicite, a new complex arsenate-molybdate from Chuquicamata, Chile
Authors: Finney J. J. , Williams S. A. , Hamilton R. D.
Published: December 2006

Obradovicite, ideal formula H4CuFe2(AsO4) (MoO4)5 · 12H2O, occurs as fine pea-green clusters on quartz from Chuquicamata, Chile. Obradovicite is orthorhombic, space group Pcnm; a = 15.046, b = 14.848, c = 11.056 Å, Z = 4. The strongest powder pattern lines are (d Å, I, hkl) 10.565(8)(110), 8.906(10)(101), 7.424(8)(020), 5.733(5)(211), 3.761(3)(400), 3.686(4)(032), 3.466(3)(411), 3.344(4)(420). It is biaxial positive with α = 1.790, β = 1.798, γ = 1.811, 2Vz = 81°, a = Z, b = X, c = Y, with strong dispersion and pale yellow pleochroism. Specific gravity is 3.55 (meas.) or 3.68 (calc.) and the Mohs hardness is 2½ with no obvious cleavage. Obradovicite is similar to betpakdalite and sodium-betpakdalite except that it contains essential Cu and K (K > Na).
Erlianite, a new vanadium- and iron-bearing silicate mineral
Authors: Feng Xiancan , Yang Ruiying
Published: December 2006

Erlianite was found in the Harhada iron deposit along the Jining-Erlian railway, Inner Mongolia Autonomous Region, People's Republic of China. The occurrence formed at a high pressure and low temperature and the mineral occurs sparingly, mainly on fracture surfaces on which there is evidence of movement. It is associated with quartz, magnetite, siderite, albite, stilpnomelane, minnesotaite, deerite, etc.

Erlianite is black with a brownish streak, silky lustre and occur as fibres, flakes, and lath-like aggregates. The grain size is 1–2 cm. It is not fluorescent. H = 3.7, D = 3.11. Cleavages on {001} and {100} are perfect; orthorhombic Pmmn or Pm21n with a = 23.20, b = 9.20, c = 13.18, Å and Z = 1. Strongest lines are 11.5(100)(200, 101), 3.05(50)(223,130), 2.89(60)(603,800,231,621), 2.61(60) (523,105,332,224), 2.52(50)(901,115,033,531), and 1.560(50) (12.0.5,14.2.0). Biaxial negative with α = 1.667, β = 1.674, γ = 1.679, 2V = 56–59°. Analysis gave SiO2 38.80, FeO 26.67, Fe2O3 21.26, V2O5 1.15, MgO 1.00, CaO 0.83, MnO 0.55, P2O5 0.051, K2O 0.079, Na2O 0.09, Al2O3 0.19, TiO2 0.38, H2O+ 7.65, H2O- 0.90, total 99.60%, leading to (Fe19.962+Fe2.193+Mg1.33Mn0.42)Σ23.90(Fe11.323+V0.68)Σ12(Si34.73Ti0.26Al0.20Fe0.813+)Σ36O90(OH,O)48 (one unit cell content for O = 138).

The sample of the new mineral was discovered in 1977 during an investigation of an iron deposit which has been named ‘M14’. The methods used for studying this mineral included optical microscopy, X-ray powder diffraction, selected area electron diffraction analysis, wet chemical analysis, DTA, TGA, infra-red absorption and Mosbauer spectroscopy.
Moolooite, a naturally occurring hydrated copper oxalate from Western Australia
Authors: Clarke R. M. , Williams I. R.
Published: December 2006

Moolooite, a naturally occurring hydrated copper oxalate has been identified in a sulphide-bearing quartz outcrop 12 km east of Mooloo Downs station homestead (25° 01′ 30″ S., 116° 06′ 30″ E.), Western Australia. It has apparently formed by the interaction of solutions derived from bird guano and weathering copper sulphides. Partial microchemical analysis indicates a composition corresponding to CuC2O4 · 0.44H2O. The infra-red spectrum is similar to that of the artificial compound with diagnostic absorption bands at 3490, 2975, 2935, 1980, 1940, 1660, 1365,1320, 830, 510, 390, and 315 cm−1. Powder X-ray diffraction patterns indicate a disordered structure with orthorhombic symmetry; a 5.35, b 5.63, c 2.56 Å, Z = 1. The strongest lines of the powder pattern are [d Å, I, hkl]: 3.88, 100, (110); 2.50, 30, (120); 2.33, 18, (011); 2.31, 25,(101); 2.14, 20, (111); 1.938, 18, (220); 1.787, 25, (121); 1.753, 30, (211); 1.216, 15, (112). Unindexed very weak diffuse lines on some patterns can be indexed assuming a supercell with a′ = a, b′ = 2b, c′ = 2c indicating the presence of ordered crystallites.

Moolooite occurs as micro-concretionary crusts and powder in cracks and solution cavities resulting from sulphide oxidation. It is found associated with opaline silica, gypsum, broehantite, antlerite, atacamite, whewellite, sampleite, and libethenite. It is turquoise-green in colour with similar streak, lustre dull to waxy, calculated density 3.43 g/cm3. Moolooite is composed of aggregates of generally sub-micrometre sized equidimensional crystallites with α ∼ 1.57 and γ ∼ 1.95.

By analogy with artificial copper oxalate, moolooite is constructed from infinite ribbon-like elementary structural units consisting of alternating Cu2+ and (C2O4)2− ions. These units are arranged en echelon in layers which are stacked with displacements so that octahedral coordination of copper ions is completed by oxygen atoms in adjacent layers. The minimal role played by water in the structure and composition of moolooite distinguish it from other oxalate minerals. Because of the zeolitic character of the water a general formula CuC2O4 · nH2O (0 ⩽ n ⩽ 1) appears to be appropriate.
Santafeite, a re-examination and new empirical formula
Authors: Dunn Pete J. , Peacor Donald R.
Published: December 2006

Santafeite, known only from New Mexico, USA, is re-examined using single-crystal X-ray and microprobe techniques. The new idealized formula, consistent with space group requirements, is

(Mn2+, Fe3+,Al,Mg)8(Mn4+, Mn2+)8 (Ca,Sr,Na)12[(VO4),(AsO4)]16(OH)20 · 8H2O.
Chrysotile and polygonal serpentine from the Balangero serpentinite
Authors: Mellini Marcello
Published: December 2006

Transmission electron microscopy shows that normal chrysotile and polygonal serpentine occur together and in parallel association with balangeroite, within the slip-veins of the Balangero serpentinite. Chrysotile substitutes for balangeroite and it is later replaced by the polygonal serpentine.

The chrysotile fibres are packed together according to a rod close-packing scheme, with defects. Lattice images of the polygonal serpentine confirm the structure model proposed by Middleton and Whittaker (1976), consisting of polygonally arranged fiat layers. This structural type is probably common for serpentine minerals and constitutes a fourth main type of layer configuration in 1:1 layer silicates.
Modelling of the relations between reaction enthalpy and the buffering of reaction progress in metamorphism
Authors: Ridley John
Published: December 2006

A proportion of the heat added to a body of rock during prograde metamorphism will be absorbed in the chemical work of metamorphic recrystallization. When and where heat is so absorbed will affect the exact thermal histories of the rocks, and hence the metamorphic textures. This paper reports the results of modelling of the inter-relations between reaction progress and thermal histories in a rock column. The results suggest that volumes of rock undergoing reaction at any moment act as heat sinks and absorb heat from the surrounding rock, that reaction generally takes place close to the temperature at which nucleation took place, and that steady heating of a rock pile can give rise to a reaction history in which spurts of reaction are separated by ‘quiet’, non-reactive intervals.
The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphism
Authors: Rubie David C.
Published: December 2006

The problems of characterizing inter-granular regions and of estimating rates of intergranular diffusion in metamorphic rocks are discussed. Inter-granular regions can be anhydrous, hydrated but under-saturated with H2O, or saturated with H2O, but only in the latter case can a free aqueous fluid phase be present. Estimates of intergranular diffusion coefficients (DIGR) at 550°C derived from a variety of published experimental work, vary from ∼ 10−8m2s−1for diffusion of species through an intergranular fluid film to ⩽ 4 × 10−24m2s−1for diffusion of SiO2or O in anhydrous grain boundaries in quartzite. Estimates ofDIGRfor hydrated grain boundaries vary from ∼ 10−13m2s−1to ∼ 10−21m2s−1; the concentration of H2O in the grain boundaries and the identity of the diffusing species (generally unknown) may be important controlling factors, and there exists the possibility of a spectrum of values between these two extremes.

Using available kinetic data it is shown that a free aqueous fluid could never have been present in parts of the basement terrane of the Sesia Zone (Western Alps) during uplift from the eclogite facies, except possibly late in the cooling history. The breakdown of sodic pyroxene + quartz occurred in response to the localized infiltration of catalytic aqueous fluid, possibly over a time interval as short as 6–6000 a, and possibly under conditions remote from equilibrium. H2O-present conditions during a dehydration reaction in metapelites of the Adula nappe (central Alps) could also have been of short duration. These examples are consistent with a model in which basement rocks at deep crustal levels are dry for long periods of time and in which the development of equilibrium mineral assemblages and microstructures generally occurs over relatively short periods of time under transitory fluid-present conditions (caused by devolatilization and/or infiltration).
Synthetic Mn-Kilchoanite—a new development in polymorphism of melilite
Authors: Kimata Mitsuyoshi
Published: December 2006

Two compounds with the chemical composition Ca2.32Mn0.68Si2.00O7 were synthesized from a molten carbonating silicate with the melilite composition. The synthetic samples were subsequently characterized by X-ray powder diffraction, IR absorption and EPMA, and they proved to be the anhydrous phases isomorphous with kilchoanite Ca3Si2O7 and åkermanite Ca2MgSi2O7 respectively, and to be polymorphous with each other. Their crystallochemical properties suggest that Mn-åkermanite is a high-temperature structure type of Mn-kilchoanite. Substitution of Mn2+ with an intermediate ionic radius between those of Mg2+ and Ca2+ cations establishes the polymorphic relationship between åkermanite Ca2MgSi2O7 and kilchoanite Ca3Si2O7.
Relationships Between Late Caledonian Lamprophyric, Syenitic, and Granitic Magmas in a Differentiated Dyke, Southern Scotland
Authors: Macdonald R. , Rock N. M. S. , Rundle C. C. , Russell O. J.
Published: December 2006

The 2 km × 5 m Newmains Dyke in the Scottish Southern Uplands consists mainly of primitive (mg number > 70), at least partly mantle-derived lamprophyre (vogesite spessartite, SiO2 50–60%), with hornblende-pyroxene-rich cumulates (SiO2 < 50%) and small amounts of quartz syenitic to granite residua (60–73% SiO2). The lamprophyres and cumulates yield an Rb-Sr whole-rock isochron age of 395±9 Ma (MSWD 2.0), and (87Sr/86Sr)i 0.70514±5—identical values to the nearby Criffell granitic pluton. After some 65% hornblende + clinopyroxene fractionation of parent lamprophyre magma, a volatile phase separated and metasomatically enriched the country rock greywackes in K, Ba, and Rb. The remaining quartz syenitic liquids became contaminated by 87Sr from these greywackes, which have a mean (87Sr/86Sr)395 value of 0.70789±114. Further fractionation of the contaminated syenitic liquids gave the granitic rocks, which have (87Sr/86Sr)395 values of 0.7056–64. The dyke appears to demonstrate in situ some of the hidden processes previously invoked to explain the evolution of the Criffell pluton itself.
Some geochemical constraints upon models for the crystallization of the upper critical zone-main zone interval, northwestern Bushveld complex
Authors: Eales H. V. , Marsh J. S. , Mitchell A. A. , de Klerk W. J. , Kruger F. J. , Field M.
Published: December 2006

Ratios between elements Mg, Fe, Co, Cr, Ni, V, and Sc are consistently different in mafic rocks of the upper critical zone, and those above the Bastard unit. Within the 300 m section above the Merensky Reef, 87Sr/86Sr ratios increase from c.0.7063 to c.0.7087, irrespective of rock type. Decoupling of Mg/(Mg + Fe2+) ratios and the Ca contents of plagioclase, and wide variations in the proportions of anorthosite within the Bastard, Merensky, and Merensky Footwall units, are inconsistent with anorthosite formation by simple fractional crystallization of magma batches of limited volume. Conversely, significant differences in Sr-isotope ratios show that these anorthosites could not have shared a common parental liquid. These data are used to develop a model whereby (a) the 300 m column above the critical zone represents the mixing of liquids of isotopically and geochemically discrete upper critical and main zone lineages, (b) mafic layers of the Bastard, Merensky, and Merensky Footwall units crystallized from discrete injections of primitive, mafic liquid while (c) the leucocratic upper parts of these units crystallized during progressive hybridization of liquid residua, which remained after significant separation of mafic phases, with a supernatant column representing the liquid residua of earlier cycles, and (d) the buoyancy of plagioclase, and enlargement of the primary phase volume of plagioclase consequent upon an increase in An/Ab ratio of hybrid liquids, were significant factors in the generation of anorthositic layers.
Silicate stages mineralogy in the later fractionation of the Insch intrusion, NE Scotland
Authors: Wadsworth W. J.
Published: December 2006

Despite poor exposures and lack of ‘stratigraphic’ control, there is consistent mineralogical and textural evidence that the Insch Upper Zone (UZ) represents a cumulate sequence developed from a single episode of progressive fractionation. This sequence has been subdivided on the basis of the phase layering, with cumulus plagioclase, pyroxenes and Fe-Ti oxides providing continuity from the Middle Zone (although the pyroxenes appear to be temporarily restricted to inter-cumulus status in the lower part of the UZ succession). The reappearance of cumulus olivine after its absence throughout the Middle Zone, marks the base of the UZ, and it is later joined by cumulus apatite, and then by alkali feldspar and zircon. Higher in the succession cumulus orthopyroxene, followed by olivine and Fe Ti oxide, eventually disappear. There is pronounced cryptic variation of the principal cumulus minerals (olivine Fo47−6, orthopyroxene En58−24, clinopyroxene Mg#63−6, plagio-clase An60−39 and the cumulus alkali feldspar is distinctly Ba-rich when it first appears. Comparison with the later fractionation stages of other layered intrusions shows broad similarities to the Bushveld and Skaergaard intrusions and closer similarities to the Fongen-Hyllingen body, which, like Insch, is a Caledonian synorogenic intrusion. The behaviour of the Insch pyroxenes, which show smoothly progressive Fe-enrichment despite their temporary absence as cumulus phases early in the UZ, together with the apparent range in cumulus plagioclase compositions in each sample, are taken to indicate that the cumulus mineral assemblages have been to some extent modified by re-equilibration with trapped inter-cumulus magma.
Evolution of the Miscibility Gap Between Muscovite and Biotite Solid Solutions with Increasing Lithium Content: An Experimental Study in the System K2O-Li2O-MgO-FeO-Al2O3-SiO2-H2O-HF at 600°C, 2 kbar PH2O: Comparison with Natural Lithium Micas
Authors: Monier Gilles , Robert Jean-Louis
Published: December 2006

This paper presents the results of an experimental study of the miscibility gap between trioctahedral and dioctahedral micas in the system K2O Li2O-MgO-FeO-Al2O3-SiO2-H2O-HF at 600°C under 2 kbar PH2O. The existence of this miscibility gap is known from previous experimental studies. The gap is large in the lithium-free system; its width reduces progressively with increasing Li content; for sufficient Li contents (Li > 0.6 atom per formula unit, based on 11 oxygens), a single Li-mica phase is obtained, intermediate between trioctahedral and dioctahedral micas. Any bulk composition located inside the miscibility gap gives an assemblage of two micas, one of the biotite-type and one of the muscovite-type. All the compositions located outside the gap, and, in particular, those belonging to the joins phlogopite-trilithionite and muscovite-zinnwaldite (or its magnesian equivalent) give a single mica phase, provided that the fluorine content is sufficient. The ratio Li/F ≈ 1 is a convenient suitable value. The types of micas and the evolutions of their compositions are well characterized by their interplanar distance d060. These experimental results allow the interpretation of most compositions of naturally occurring lithium micas, in the range 0 ⩽ Li ⩽ 1 a./f.u. Natural micas of biotite-type and muscovite-type are located on both sides of the miscibility gap and their compositions get closer with increasing Li content.
Babingtonite and Fe-rich Ca-A1 silicates from western Southland, New Zealand
Authors: Duggan M. B.
Published: December 2006

Babingtonite is a common constituent of calcareous volcanic detritus in the interstices of pillow lavas from an outcrop of the Takitimu Group, western Southland, New Zealand, Associated minerals include Fe-rich prehnite (Fe/(Fe+Al) = 0.12–0.33), Fe-rich epidote (Ps24–53), grandite garnet (av. Andradite70 Grossular30), quartz, calcite, chlorite, and pumpellyite. Babingtonite shows little departure from its ideal composition other than minor Mg, Mn, and Al and a trace of Na.

Textural evidence and microprobe data suggest that the babingtonite, Fe-rich epidote, calcite, and quartz formed from hydrothermal solutions by direct precipitation in open cavities and by replacement of higher temperature silicate phases (in particular plagioclase and basaltic glass) in a shallow marine volcanic environment. During subsequent burial and low-grade metamorphism babingtonite was partially replaced by prehnite, less Fe-rich epidote, grandite, and chlorite.
Johninnesite, a arsenosilicate from new sodium manganese the Kombat Mine, Namibia
Authors: Dunn Pete J. , Peacor Donald R. , Su Shu-Chun , Nelen Joseph A. , von Knorring Oleg
Published: December 2006

Johninnesite, ideally Na2Mg4Mn12As5+2 Si12043(OH)6,, is triclinic, P1 or P1̄, with a = 10.44(2), b = 11.064(6), c = 9.62(1) Å, α = 107.43(7), β = 82.7(1), γ = 111.6(1)°, V = 894(2) Å3, and Z = 1. It occurs as yellow-brown fibrous aggregates, associated with rhodonite, kentrolite, and richterite, from the Kombat Mine in Namibia. Johninnesite has cleavages on {100} and {010}, density of 3.48 (meas.), 3.51 (calc.) g/cm3. It is biaxial negative, with 2Vx = 41.9°, α = 1.6742(4), β = 1.6968(3), γ = 1.6999(3); dispersion r > υ, distinct.
Benleonardite, a new mineral from the Bambolla mine, Moctezuma, Sonora, Mexico
Authors: Stanley C. J. , Criddle A. J. , Chisholm J. E.
Published: December 2006

Benleonardite, ideally Ag8(Sb,As)Te2S3 with Sb > As, is a new mineral species that occurs in ore specimens collected from the dumps of the disused Bambolla mine, Moctezuma, Mexico. The associated minerals are acanthite, hessite, an unnamed Ag4TeS phase, pyrite, sphalerite, and native silver. Together with benleonardite, these form thin black crusts in fractures filled with quartz and dolomite in highly altered, tuffaceous, andesitic and rhyolitic rocks. Benleonardite is an opaque mineral and, in reflected plane-polarized light in air, it is weakly bireflectant from very pale light blue to slightly darker blue. It is not pleochroic. Luminance values (relative to the CIE illuminant C) for Ro and R′e computed from visible spectrum reflectance data for the most bireflectant grain, are 33.6 and 31.7% in air, and 18.3 and 16.5% in Zeiss oil (ND 1.515) respectively. Vickers micro-indentation hardness is 105–125 (VHN25). The X-ray powder diffraction pattern could be indexed on a tetragonal cell with a 6.603(5) and c 12.726(6) Å; for Z = 2, the calculated density is 7.79 g/cm2 for the average analysis. The strongest five lines in the X-ray powder pattern are [d in Å (I) (hkl): 12.7 (70) (001); 3.188 (30) (021,004); 2.936 (100) (022); 2.608 (35) (023); 2.158 (35) (124).
A computer simulation of the structure and elastic properties of MgSiO3 perovskite
Authors: Wall A. , Price G. D. , Parker S. C.
Published: December 2006

The structure and elastic properties of MgSiO3, a major mantle-forming phase, have been simulated using computer models which predict the minimum energy structure by using interatomic pair potentials to describe the net forces acting between the atoms. Four such interatomic potentials were developed in this study, and are compared with potential N1 of Miyamoto and Takeda (1984). The most successful potential (W3) was derived by fitting the short range potential parameters to both the experimentally obtained structural and elastic properties of MgSiO3 perovskite. The relative stabilities of some of the possible perovskite polymorphs, the orthorhombic, cubic, and tetragonal phases and hexagonal polytypes, were evaluated at 0 K and between 1 bar and 2 Mbar. The orthorhombic phase is found to be stable at all but the highest pressures, where the cubic phase may be stable. The temperature of the ortho-rhombic to cubic transition may decrease with increasing pressure. The energy of a stacking fault on (110) in the cubic phase was estimated using the ANNNI model and found to be about 1.95 J m−2 using potential W3. The distance of separation of partial dislocations of this type is predicted to increase with increasing pressure from 8.4 Å at 1 bar to 9.2 Å at 1 Mbar.
Crystal structure and cation distribution in freibergite and tetrahedrite
Authors: Peterson R. C. , Miller I.
Published: December 2006

The crystal structure of a freibergite (Ag-tetrahedrite) from Keno Hill, Yukon, Canada, and a tetrahedrite from Turquetil Lake, NWT, Canada, have been refined. The freibergite, Cu5.84Ag4.22Fe1.59Zn0.43 Sb4.10AS0.13S13, a = 10.610(2) Å, and the tetrahedrite, Cu10.24Fe1.03Zn0.97Ag0.05Sb3.66As0.28S13, a = 10.364(2) Å, were both refined in space group I4̄3m. The refinements confirm that Ag does occupy the threefold coordinated metal site as first described by Kalbskopf (1972) and that Fe also occupies this site. The structural changes accompanying Ag substitution are described and a model to explain the upper limit of substitution at four atoms of silver for thirteen atoms of sulphur is proposed.
A study of the thickness of ferrihydrite coatings on kaolinite
Authors: Jones Angela A. , Saleh Adil M.
Published: December 2006

The form and thickness of the ferrihydrite coating on kaolinite basal surfaces was studied in mixes containing 1–10% ferrihydrite through a combination of TEM, shadowed replicas, selected area electron diffraction, and determinations of surface area and distribution of charge on the surfaces. At pH3 the ferrihydrite was found to attach initially as single particles to certain sites on the kaolinite. These particles grew laterally and vertically until with 4% ferrihydrite they were aggregates of from 8 to 25 layers of particles. With more ferrihydrite the aggregates coalesced. Despite the irregular cover on the kaolinite satisfactory electron diffraction patterns were obtained and as little as 2% ferrihydrite was detected in a mixture at pH3.
High-pressure, synthetic loveringite-davidite and its rare earth element geochemistry
Authors: Green T. H. , Pearson N. J.
Published: December 2006

Loveringite-davidite members of the crichtonite group were synthesized at high pressure and temperature (7.5 kbar, 1000–1050 °C) from a melt of TiO2 and rare earth element (REE) enriched basaltic andesite composition. Four sets of partition coefficients for La, Srn, Ho, Lu and Sr (analogue for Eu2+) were obtained. These show that light and heavy REE are readily accommodated, but the intermediate REE are discriminated against in the loveringite—davidite structure. This confirms the previously proposed two sites (A and M) for REE substitution in the crichtonite group. Additional experiments verified the stability of REE-rich crichtonite group minerals to 20 kbar, 1300 °C and 30 kbar, 1000 °C, and indicate that this phase may be an important accessory repository for the light and heavy REE in the upper mantle.
Sector-zoned kaersutite in camptonites from Morocco
Authors: Mokhtari Abdelkader , Velde Danielle
Published: December 2006

Camptonites from the Taourirt region of Morocco contain kaersutite crystals that exhibit clear sector zoning. The electron microprobe reveals systematic variations between sectors, with preferential enrichment of Mg and Si in sector (011) and higher values for Fe, Ti and Al in sectors (110) or (100). These differences are similar to those recorded in clinopyroxenes with hour-glass zoning where this type of crystallization has been known for more than a century.
Oxygen fugacity variations and mineral reactions in sapphirine-bearing paragneisses, E. Grenville province, Canada
Authors: Herd R. K. , Ackermand D. , Thomas A. , Windley B. F.
Published: December 2006

Sapphirine-bearing assemblages occur in paragneisses in a 200 km long block in the Grenville province in Labrador-Quebec. The occurrence of some of these rocks was previously known, but their considerable extent is now recognised from regional mapping. The mineral assemblages, reactions, and compositions and the tectonic structure in the paragneisses of this block are surprisingly uniform. Within feldspar-quartz layers we recognise assemblages with sapphirine, quartz, iron titanium oxides, spinel, corundum, diaspore, orthopyroxene, sillimanite, cordierite, garnet, and biotite in metre to millimetre-thick layers. These minerals reacted with their matrix, especially quartz, during cooling and uplift. At least 11 retrograde reactions gave rise to spectacular corona textures and define a P-T-time trajectory from c. 8 kbar at 900 °C to 6 kbar at 700 °C which changed from early isobaric to late isothermal. Based on successive generations of sapphirine and orthopyroxene with constant XMg and decreasing Fe3+/Fe2+ ratio in recalculated formulae, we deduce an accompanying change from high to low oxygen fugacity along this trajectory. The isothermal section of the trajectory is consistent with predicted rapid uplift and with field evidence for thrust tectonics and mylonitisation.
Mineralogy and metamorphic history of norite dykes within granulite facies gneisses from Sand Mata, Rajasthan, NW India
Authors: Sharma Ram S. , Sills Jane D. , Joshi M.
Published: December 2006

Metanorite dykes intrude the Banded Gneiss Complex at various places in Rajasthan, N.W. India. They show neither chilled margins nor gradational contacts with the country rock amphibolite or granulite facies gneisses. They have ophitic to subophitic texture with strongly zoned subcalcic clinopyroxene and orthopyroxene, olivine and plagioclase, with subsidiary biotite. During slow cooling a series of reaction coronas developed with garnet forming round biotite, ilmenite and orthopyroxene; hornblende round pyroxenes and orthopyroxene, hornblende ± spinel round olivine, which may be totally replaced. It is inferred that the dykes crystallised from a tholeiitic magma at about 1100-1150 °C and were intruded during the waning stages of granulite facies metamorphism. The corona minerals grew at about 650–700 °C. A series of reactions to account for the development of the coronas is proposed using measured mineral compositions. Although these reactions do not balance for individual corona formation, metamorphism was probably isochemical with Ca, Na, K, Ti, Si and H2O only mobile on the scale of a thin section. Si and H2O were possibly mobile on a larger scale.