bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer simulation of a microstructure in a potassium feldspar
Authors: Tsatskis I. , Salje E. K. H.
Published: December 2006

Kinetics of atomic ordering in a potassium feldspar is simulated using massively parallel computing. The simulation method is based on the Monte Carlo algorithm for the Al-Si redistribution (the Kawasaki dynamics) combined with the lattice relaxation. The Hamiltonian has the symbolic form

where u represents displacements of atoms from ideal positions, and p the Al and Si occupation numbers. The model is purely elastic; there is no direct interaction between Al and Si atoms. The simulated crystal is a thin film with (010) surfaces and consists of 64 × 64 unit cells; the unit cell defined for the whole film contains slightly more than 4 formula units. The (010) orientation is chosen in order to preserve in the film the main structural feature of feldspars: crankshaft-like sheets formed by four-tetrahedra rings. This makes it possible to observe the Pericline twins only. At the late stage of the kinetic run these twins are clearly seen. The direction for the domain walls is determined by the spontaneous strain and changes with the change of the model parameters; considerable local deviations from this direction are observed.
Rigid unit modes in framework silicates
Authors: Dove Martin T. , Heine Volker , Hammonds Kenton D.
Published: December 2006

We describe a model for framework silicates in which the SiO4 (and AlO4) tetrahedra are treated as perfectly rigid and freely jointed. From this model we are able to identify low-energy modes of distortion of the structure, which we call Rigid unit modes. These modes can act as soft modes to allow easy distortions at phase transition. We discuss three forces that will operate at a phase transition in conjunction with the candidate soft modes to determine which of the rigid unit modes will actually precipitate a phase transition, and illustrate these ideas by detailed discussions of the phase transitions in quartz, leucite and cristobalite. The model can also be used to estimate the transition temperature, and the theory highlights an important role for the stiffness of the tetrahedra.
Synthesis and Rietveld crystal structure refinement of mackinawite, tetragonal FeS
Authors: Lennie A. R. , Redfern S. A. T. , Schofield P. F. , Vaughan D. J.
Published: December 2006

Mackinawite, tetragonal FeS, has been synthesised by reacting iron with Na2S solutions. A Rietveld structure refinement of X-ray powder diffraction data, recorded using X-rays monochromated from synchrotron radiation with a wavelength of 0.6023 Å, has been performed. The structure has been refined in the tetragonal space group,P4/nmm, and has the following cell parameters:a= 3.6735(4),c= 5.0328(7) Å, V = 67.914(24) Å3. Our refinement shows that the FeS4tetrahedron in mackinawite is almost perfectly regular, with a much smaller distortion than has been previously reported. An improved X-ray diffraction data set is provided.
The system Pd-Fe-Ni-S at 900 and 725°C
Authors: Makovicky Emil , Karup-Møller Sven
Published: December 2006

The system Pd-Fe-Ni-S was studied at 900 and 725°C by means of dry condensed charges. At both temperatures it is dominated by the phase relationships involving sulphide melt. Pd-Fe-Ni alloys with broad miscibility primarily coexist with the melt; they are relatively enriched in Pd, whereas the associated melt is enriched in Ni. With decreasing temperature the melt recedes from Fe-rich regions. The incompatibility of PdS (extensive solid solution with Ni) andmssat 900°C is replaced by their co-crystallization (± disulphide(s) of Ni,Fe or ± sulphide melt) at 725°C The Ni/Fe ratio in the melt changes regularly against that inmsswith increasing S fugacity and Pd contents in these two phases. (Ni,Fe)3±xS2and Pd4S play important roles at 725°C. The data offer an array of distribution coefficients and solubility values suitable for geological interpretations.
High-thorium monazite-(Ce) formed during disequilibrium melting of metapelites under granulite-facies conditions
Authors: Watt Gordon R.
Published: December 2006

Monazite is a light rare-earth element (LREE)-bearing accessory phase common in felsic granitic rocks, and strongly influences LREE concentrations in granites and the chemistry of melts and residues formed during partial melting. Cheralite-rich (high-Th) monazite-(Ce) has been recorded as rims on partially dissolved cores in a suite of granulite-facies migmatites generated by disequilibrium melting. High-Th monazite has previously been recorded only in granitic-pegmatite occurrences. Subidiomorphic monazite-(Ce) from leucosome, melanosome and mesosome consists of complexly zoned cores (up to 300 µm in diameter) containing 5.17–9.87 wt.% ThO2, overgrown by essentially unzoned rims (containing up to 21.4 wt.% ThO2). Uranium contents are average for Th-rich monazite-(Ce) (0.22–3.17 wt.% UO2). Th enrichment (relative to LREE) in monazite-(Ce) rims is ascribed to the presence of fluorine-bearing melts (formed during the incongruent breakdown of biotite to produce a water-undersaturated melt), allowing the formation of REE-fluoride complexes in the melt, coupled with the increased charge balanced substitutions Th4+ + Si4+ ⇌ REE3+ + P5+ and Th4+ + Ca2+ ⇌ 2REE3+ into monazite-(Ce). Fractionation of Th and U (reflected by an increased in Th/U in rims relative to cores) may have occurred due to the removal by a CO2-rich fluid phase in the melt. These interpretations are consistent with elevated CO2 and F contents of granitic liquids produced during the water-undersaturated breakdown of biotite under granulite-facies conditions. Evidence for restricted monazite-(Ce)-melt equilibration and rapid melt removal is provided by the ubiquitous presence of partially embayed cores and unzoned rims.
Anorthite megacrysts from island arc basalts
Authors: Kimata Mitsuyoshi , Nishida Norimasa , Shimizu Masahiro , Saito Shizuo , Matsui Tomoaki , Arakawa Yoji
Published: December 2006

Anorthite megacrysts are common in basalts from the Japanese Island Arc, and signally rare in other global fields. These anorthites are 1 to 3 cm in size and often contain several corroded Mg-olivine inclusions. The megacrysts generally range from An94Ab4Ot2 to An89Ab6Ot5 (Ot: other minor end-members, including CaFeSi3O8, CaMgSi3O8, AlAl3SiO8, □Si4O8) and show no chemical zoning. They often show parting. Redclouded megacrysts contain microcrystals of native copper with a distribution reminiscent of the shape of a planetary nebula. Hydrocarbons are also present, both in the anorthite megacrysts and in the olivines included within them. Implications of lateral variations in the Fe/Mg ratio of the included olivines, in Sr-content and in Sr-isotope ratio of the anorthite megacrysts with respect to the Japanese island arc, relate to mixing of crustal components and subducted slab-sediments into the basaltic magmas.
Distribution of trace elements in feldspars of granitic aplites and pegmatites from Alijó-Sanfins, northern Portugal
Authors: Neiva A. M. R.
Published: December 2006

At Alijó-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization. Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Ba, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.
Excess free energies of mixing of Sr,Ba-bearing binary feldspar solid solutions (experimental data)
Authors: Kotelnikov A. R. , Chernysheva I. V.
Published: December 2006

The distribution of potassium and strontium, potassium and barium between feldspars and aqueous chloride solutions was studied at 700°C, 2 kbar and 800°C, 2 kbar respectively. The distribution of Sr and Ba between coexisting feldspar and chloride solutions is not ideal; Sr and Ba are enriched in feldspar relative to solution. In order to estimate the phase state of the chloride solutions, special experiments were conducted using the synthetic fluid-inclusion method in the systems KCl-BaCl2-H2O and KCl-SrCl2-H2O at 700–800°C, 2 kbar. It was shown that (0.5M KCl+0.5M SrCl2) aqueous solution is homogeneous at 800°C, 2 kbar. The 0.25–0.5M SrCl2 solutions are homogeneous at 700°C 2, kbar. The (0.5M KCl+0.5M BaCl2) solution is homogeneous at 700°C, 2 kbar and heterogeneous at 800°C, 2 kbar. Margules parameters for describing the excess energy of mixing of the (K,Sr)- and (K,Ba)-feldspar solid solutions were calculated. The integrated values of excess energy of mixing () were estimated for the different binary feldspar solid solutions, and a correlation of with the crystallochemical parameter ρ = (RA-RB)/D(Me-O) was observed. Feldspar solid solutions can be subdivided into three groups based on the relationship between , p and the stability of the solid solution.
Photo-emission electron microscopy (PEEM) heating investigations of a natural amphibole sample
Authors: Wartho J.-A.
Published: December 2006

PEEM allows ‘real-time’ observations to be made of solid-state transformations and other high-temperature processes taking place during vacuum-heating up to c. 2000°C The solid state transformations of an amphibole-rich hornblendite specimen have been observed in the temperature range of 750–1000°C (± 50°C Between c. 970–990°C a rapid change in orientation contrast was observed, indicating a structural rearrangement from an oxyhornblende crystal lattice to a clinopyroxene structure. This phase retains the original amphibole shape and texture (including two 120°C intersecting cleavage traces), but possesses a clinopyroxene crystal structure. At higher temperatures this phase is seen to decompose, forming iron oxides and other fine-grained products. PEEM has provided useful information on both the nature and rates of transformation of natural amphiboles which has proved invaluable in our understanding of the mineralogically-controlled mechanisms of argon release during 40Ar/39Ar dating of amphibole samples.
Kintoreite, PbFe3(PO4)2(OH,H2O)6, a new mineral of the jarosite-alunite family, and lusungite discredited
Authors: Pring A. , Birch W. D. , Dawe J. , Taylor M. , Deliens M. , Walenta K.
Published: December 2006

Kintoreite is a new lead iron phosphate mineral in the alunite-jarosite family, from Broken Hill, New South Wales, Australia. It is the phosphate analogue of segnitite and the iron analogue of plumbogummite. Kintoreite occurs as clusters and coatings of cream to yellowish green rhombohedral crystals up to 2 mm high and with the principal form {112}. The mineral also forms waxy, yellowish green globular crusts and hemispheres on other phosphate minerals. These associated species include pyromorphite, libethenite, rockbridgeite/dufrenite, apatite and goethite. Kintoreite formed during oxidation of primary ore rich in galena, in the presence of solutions with high P/(As + S) ratios. The mineral is named for the locality, the Kintore opencut, in which it is most common. A mineral closely resembling kintoreite in composition has also been found at several mines in Germany. Type material is preserved in the Museum of Victoria and the South Australian Museum.

Electron microprobe analysis showed a nearly complete spread of compositions across the P-dominant portion of the segnitite-kintoreite series. The selected type specimen has an empirical formula of Pb0.97(Fe2.95Zn0.13Cu0.02)Σ3.10[(PO4)1.30(AsO4)0.39(SO4)0.18(CO3)0.11]Σ1.98(OH)5.45·0.74H2O, calculated on the basis of 14 oxygens and with all Fe trivalent. The simplified formula is PbFe3(PO4)2(OH,H2O)6. Kintoreite crystals are translucent with a vitreous to adamantine lustre, with globules appearing waxy. The streak is pale yellowish green and the Mohs hardness is ∼ 4. Crystals show good cleavage on {001} and are brittle with a rough fracture. The calculated density is 4.34 g cm−3. Kintoreite crystals are uniaxial negative with RIs between 1.935 and 1.955 and show light yellowish green to medium yellow pleochroism.

The strongest lines in the X-ray powder pattern are (dobs, Iobs, hkl) 3.07(100) 113; 5.96(90)101; 3.67(60)110; 2.538(50)024; 2.257(50)107; 1.979(50)303; 1.831(40)220. The X-ray data were indexed on a hexagonal unit cell by analogy with beudantite, giving a = 7.325(1) Å, c = 16.900(3) Å, V = 785.3(5) Å3 and Z = 3. The probable space group is Rm, by analogy with beudantite and other members of the alunite-jarosite family. Powder X-ray diffraction data for several intermediate members suggest that the segnitite-kintoreite series may not represent ideal solid solution.

During the study of kintoreite, part of the type specimen of lusungite from Zaïre was obtained and shown to be goyazite. The IMA's Commission on New Minerals and Mineral Names has voted to discredit lusungite as a species, and has approved the renaming of the ‘lusungite’ group as the segnitite group. However, as relationships between crystal structure, order-disorder and solid solution in the Pb-rich minerals of the alunite-jarosite family are not well documented, the nomenclatural changes resulting from this study should be seen as interim only.
The crystal structure of vlodavetsite, AlCa2(SO4)2F2Cl·4H2O
Authors: Starova G. L. , Filatov S. K. , Matusevich G. L. , Fundamensky V. S.
Published: December 2006

Absract

The crystal structure of vlodavetsite, AlCa2(SO4)2F2Cl·4H2O, has been determined, space group I4/m, a = 6.870(1), c = 13.342(2) Å, Z = 2, Dx = 2.35 g/cm3. The polyhedron cation chains are parallel to [001] and consist of couples of distorted Ca octahedra alternating with one distorted Al octahedron rotated through 24° with respect to the former. The chains are linked by SO4-tetrahedra so that all of the four tetrahedron oxygen atoms take part in coordination of Ca atoms to form a distorted octahedron with Cl and F atoms. The Al coordination polyhedron consists of two F atoms and four oxygen atoms belonging to water molecules. There is a specific interaction via hydrogen bonds between oxygen atoms of SO4-tetrahedra and water molecules.
Picrite sills and crystal-melt reactions in the Honningsvåg Intrusive Suite, northern Norway
Authors: Tegner Christian , Robins Brian
Published: December 2006

Field relations in the upper part of Intrusion II of the Caledonian Honningsvåg Intrusive Suite show that some peridotite sheets transgress, and include in situ rafts of, the adjacent gabbroic cumulates. Modal and textural analyses of three olivine melagabbro sheets show non-cotectic mineral proportions that are likely to result from crystal-melt reactions. Discordant, replacive fingers and pipes of feldspathic peridotite along interfaces between peridotite and overlying olivine melagabbro also suggest crystal-melt reactions.

It is proposed that several picritic sills intruded porous gabbroic cumulates in the upper part of Intrusion II. Lateral infiltration of picritic magma led to crystal-melt reactions, mainly assimilation of plagioclase and precipitation of olivine, resulting in the formation of olivine melagabbro and peridotite sheets, and replacive fingers and pipes of feldspathic peridotite.
The production of chemically stratified and adcumulate plutonic igneous rocks
Authors: Tait Stephen R. , Jaupart Claude
Published: December 2006

We review recent advances on the physical principles of crystallization in multicomponent systems, and use them to provide a framework for interpreting petrological and geochemical observations from igneous intrusions. The thermal structure of crystallizing boundary layers imposes strong constraints on the chemical and mineralogical compositions of the solid that can form from a given melt. The thermal problem is largely independent of the chemical composition of the melt, and sets the course of crystallization. A key problem to understand is the temperature of the solidification front (which we take to mean that point at which the last drop of liquid solidifies) particularly in the geologically relevant case in which the temperature at the cold boundary is below the eutectic temperature. Focussing on the solidification front rather than on the liquidus is a valuable perspective. Adcumulus growth requires specific conditions and much can be learned from trying to understand how these can develop from given starting conditions. We discuss the physical reasons and field evidence for the existence of mushy layers, where solid fraction and temperature vary by large amounts. In such regions of the magma chamber, thermodynamic equilibrium is nearly achieved locally and, for a given temperature, this specifies the composition of the interstitial melt. Thus, in a magma chamber, the whole liquid line of descent is present simultaneously. Compositional convection is likely to set in, and this exchange between the interior of the mushy layer and the main reservoir leads to a chemically stratified solid, and to adcumulus growth. The contribution of crystal settling to the floor cumulates is evaluated as a function of the magnitude of convective heat flux through the roof. It is shown that crystal settling is unlikely to overwhelm in-situ nucleation and growth at the floor.
Melt movement and the occlusion of porosity in crystallizing granitic systems
Authors: Bryon D. N. , Atherton M. P. , Cheadle M. J. , Hunter R. H.
Published: December 2006

Porosity occlusion has been studied in a granodiorite rock from the Peruvian Coastal Batholith. The texture of the granodiorite is characteristic of Cordilleran I-type rocks, and the textural relations and modelled crystallization path within the quaternary An-Ab-Or-Qz system indicate alkali feldspar was the last major phase to start crystallizing. In thin section, alkali feldspar crystals occur both as large anhedral ‘plates’ containing numerous inclusions, and small interstitial cuneiform ‘pockets’. The alkali feldspar pockets are interpreted as late stage nucleation and growth of new crystals in pores that became isolated from the larger crystals during the latter stages of crystallization. Their geometry therefore mirrors that of the pores immediately after isolation.

From the modal abundance of the interstitial pockets, and taking into account contemporaneous growth of the other major phases, it is suggested that crystallization in isolated pores involved solidification of the final 3–4% of liquid. Alkali feldspar growth on the rims of the large anhedral plates prior to pore isolation is evidence for the localised (mm-cm scale) diffusion of chemical species within the interconnected melt phase. However, Rayleigh number calculations indicate that the separation of melt from crystals by compositional convection is unlikely to have occurred during interstitial crystallization.
The generation of small melt-fractions in truncated melt columns: constraints from magmas erupted above slab windows and implications for MORB genesis
Authors: Hole Malcolm J. , Saunders Andy D.
Published: December 2006

At a number of locations along the Pacific margin of the Americas and west Antarctica, small volumes of alkalic basalts were erupted following successive ridge crest-trench collisions. The basalts were generated as a result of upwelling of asthenosphere through windows in the subducted plate. There is no evidence for local high temperature mantle plumes or significant lithospheric extension associated with these basalts. For the best sampled area, the Antarctic Peninsula, mean values for fractionation-corrected iron content (FeO*) vary from 6.9 to 10.6 wt.%, and for Na2O (Na8.0) from 3.25 to 4.6 wt.%, implying generation of small melt-fractions at variable mean pressures. The results of rare earth element inversion modelling yield a melt generation interval of 100 to 52 km, with a maximum melt fraction of c. 7% generated from a MORB-like source atTp1300°C. Trace element and isotope systematics are also consistent with the generation of the basalts from a MORB-like source.

Mean pressures of melt generation increase with increasing distance from the original trench, but trace element and Na8.0data suggest that there is no systematic variation in extent of melting with distance from the trench. The data are consistent with a model whereby a MORB melting column, initially intersecting the peridotite solidus at between 15 and 30 kbar, is truncated by a lithospheric cap which thickens fromc. 15–20 km (≈ 5–8 kbar) up to a maximum of c. 50 km (≈ 15 kbar), such that the mean pressures of melting increase with increasing distance from the palaeo-trench. The MORB-like major element geochemistry of basalt samples closest to the ancestral trench are consistent with initial intersection of the peridotite solidus at low pressures (c. 15 kbar). For areas of thickest lithosphere, mean pressures of melt generation are higher, but extents of melting are lower than for a MORB melting column with a similar initial pressure of intersection of the peridotite solidus. All these basalts therefore potentially represent analogues for the small melt-fraction precursors to the generation of MOR tholeiites.

Thermal constraints suggest that these low volume, small melt-fractions, were generated with CO2on the solidus, because mean pressures of melt generation are greater than the pressure of intersection of theTp1300°C mantle adiabat and the dry peridotite solidus. Potentially, all MORB may be generated initially with CO2on the solidus, and if this is correct, it does not require thermal anomalies to generate large extents of melting at high mean pressures.
Bismuth-bearing assemblages from the Northern Pennine Orefield
Authors: Ixer R. A. , Young B. , Stanley C. J.
Published: December 2006

Bismuthinite-bearing quartz veins from the Alston Block of the North Pennine Orefield are all close to, or above, the Rookhope and Tynehead cupolas of the buried Weardale Granite. They are uniform in composition and paragenesis and are earlier than the main fluorite-baryte-galena-sphalerite mineralization of the orefield. Rhythmical crystallization of quartz, chalcopyrite and minor pyrite is followed by fluorite-quartz-chalcopyrite-minor sphalerite-altered pyrrhotite mineralization. Early tin-bearing (up to 0.29 wt.% Sn) chalcopyrite encloses trace amounts of bismuthinite (Bi2S3), synchysite (CaREE(CO3)F2), argentopentlandite (Ag(FeNi)8S8) (close to being stoichiometric), pyrrhotite, cubanite and cosalite (Pb2Bi2S5), while early pyrite carries monoclinic pyrrhotite (close to Fe7S8) and tungsten-bearing cassiterite (up to 1.03 wt.% WO3). Bismuthinite is macroscopically visible and is associated with native bismuth and small, fine-grained, spherical aggregates that qualitative analysis suggests may be cosalite crystals. Synchysite and more rarely monazite, xenotime and adularia are intergrown with bismuthinite. These mineralogical data form part of the basis for an increasing awareness of the contribution of the Weardale Granite to the early phases of mineralization in the Alston Block.
Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy
Authors: Carbonin Susanna , Russo Umberto , Della Giusta Antonio
Published: December 2006

Three natural spinels of different places of occurrence and compositions were investigated by means of microprobe chemical analysis, single crystal X-ray diffraction and Mössbauer spectroscopy. All cation distributions between T and M sites were calculated from microprobe and XRD experimental data, by means of a mathematical model with appropriate assumptions. Fe2+ and Fe3+ assignments calculated in this way were compared with those observed in Mössbauer spectra. The satisfactory agreement found proves, at least in the samples studied, the reliability of the model and the assumptions used. In the spinels examined, such results show Fe2+ and Fe3+ virtually ordered in T and M sites respectively. Mössbauer data also revealed Fe2+ in different tetrahedral sites due to the next-nearest neighbour effect, probably as a consequence of spinel genetic conditions.
Noélbensonite, a new BaMn silicate of the lawsonite structure type, from Woods mine, New South Wales, Australia
Authors: Kawachi Y. , Coombs D. S. , Miura H.
Published: December 2006

Noélbensonite, a new mineral, is the barium manganese analogue of lawsonite. It is described from the Woods ornamental rhodonite mine, 30 km NNE of Tamworth, New South Wales, Australia, where it occurs as aggregates of blocky to sometimes lamellar crystals ranging from a few micrometres to (rarely) 100 µm in length. It replaces NaMn amphibole, namansilite, and pectolite, and also occurs as tiny monomineralic veinlets 0.05–0.25 mm thick. Rare euhedral crystals are dominated by {100} and {011}, with (011) ^ = 68°. The mineral is orthorhombic, space group apparently Cmcm; a = 6.325(1), b = 9.120(1), c = 13.618(1) Å, V = 785.6(1) Å3, with a : b : c = 0.694 : 1 : 1.493. Noélbensonite is brittle, fracture irregular, Mohs hardness about 4, cleavage and twinning not observed, colour dark brown, streak paler yellow-brown, lustre earthy on some veinlet surfaces to brilliantly vitreous, calculated density 3.87 g/cm3, refractive indices α = 1.82(1),β (calculated from 2V) = 1.835(10), γ = 1.85(1), biaxial negative 2Vα = 46°(3°), strong dispersion r > v, straight extinction to plane of flattening, {100}, α ∥ c, β ∥ b, γ ∥ a with pleochroism in very thin sections: α = orange yellow, β = orange, γ = brownish orange, absorption γ > β ⇐p; α. The average of 23 electron microprobe analyses (wt.%) is SiO2 26.02, Al2O3 0.17, TiO2 0.01, Fe2O3 0.19, Mn2O3 34.76, CaO 0.31, Na2O 0.14, BaO 29.08, SrO 1.51, H2Ocalc 7.87, total 100.06, leading to the simplified formula . Up to 15% Sr and 9% Ca substitute for Ba in the large-cation sites. The strongest lines in the X-ray powder diffraction pattern are [(Iobs) dobs/Å hkl] (100) 4.85 111; (50) 4.557 020; (59) 4.322 021; (77) 3.416 113,004; (80) 2.869 202; (47) 2.849 114; (82) 2.729 024; (45) 2.543 132; (48) 2.428 222; (38) 2.255 223,041. The name is for William Noél Benson (1885–1957), in honour of his classic researches in the New England Fold Belt and of his tenure of the Chair of Geology at the University of Otago.
Subsilicic sodium gedrite in leptite of quartz keratophyric origin, Nordmark (Sweden)
Authors: Linthout Kees , Lustenhouwer Wim J.
Published: December 2006

The Mg—Fe orthoamphibole series □ (Mg, Fe)7Si8O22(OH)2 — Na(Mg, Fe)5- Al2Si5Al3O22(OH)2 has an open end in the sense that the Si5 end member has not been found in nature; tiny domains of near end–member composition in intricately zoned crystals (Schumacher, 1980; Robinson et al. 1982), appeared to be intergrowths of two different double-chain silicates (Schumacher, pers. comm., 1994).
Length scale dependence of high-pressure amorphization: the static amorphization of anorthite
Authors: Redfern Simon A. T.
Published: December 2006

High-pressure amorphization of anorthite has been observed by energy-dispersive X-ray diffraction of powdered samples held under static pressure in a diamond anvil cell. The onset of amorphization is accompanied by a significant reduction in the intensity of Bragg reflections at pressures between 10 and 14 GPa, and anorthite becomes completely X-ray amorphous between 14 and 20 GPa. These pressures are significantly lower than those suggested by earlier birefringence studies. The discrepancy can be reconciled in terms of a model of high-pressure amorphization in which partially amorphized anorthite can be regarded as a spatially heterogeneous anti-glass, with long-range order maintained but translational disorder dominating at shorter correlation lengths.
Morinite from Gunheath China Clay Pit, St Austell, Cornwall
Authors: Elton N. J. , Hooper J.J. , Coggon L.
Published: December 2006

Morinite, NaCa2A12(PO4)2(OH)F4.2H2O, is a lowtemperature hydrothermal phosphate found in granite and granite-pegmatite environments. It was first described by Lacroix in 1891 from Montebras, France (see Palache et al., 1951) where it occurred as rose coloured prismatic crystals with amblygonite, wardite, wavellite, apatite and cassiterite. Morinite is also known from Germany, Finland (Roberts et al., 1990) and the USA (Fisher and Runner, 1958; Fisher, 1960).
Leisingite, Cu(Mg,Cu,Fe,Zn)2Te6+O6·6H2O, a new mineral species from the Centennial Eureka mine, Juab County, Utah
Authors: Roberts Andrew C. , Groat Lee A. , Grice Joel D. , Gault Robert A. , Jensen Martin C. , Moffatt Elizabeth A. , Stirling John A. R.
Published: December 2006

Leisingite, ideally Cu(Mg,Cu,Fe,Zn)2Te6+O6·6H2O, is hexagonal, P3 (143), with unit-cell parameters refined from powder data: a = 5.305(1), c = 9.693(6) Å, V = 236.2(2) Å3, c/a = 1.8271, Z = 1. The strongest six reflections of the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 9.70 (100) (001), 4.834 (80) (002), 4.604 (60) (100), 2.655 (60) (110), 2.556 (70) (111) and 2.326 (70) (112). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah U.S.A. where it occurs as isolated, or rarely as clusters of, hexagonal-shaped very thin plates or foliated masses in small vugs of crumbly to drusy white to colourless quartz. Associated minerals are jensenite, cesbronite and hematite. Individual crystals are subhedral to euhedral and average less than 0.1 mm in size. Cleavage {001} perfect. Forms are: {001} major; {100}, {110} minute. The mineral is transparent to somewhat translucent, pale yellow to pale orange-yellow, with a pale yellow streak and an uneven fracture. Leisingite is vitreous with a somewhat satiny to frosted appearance, brittle to somewhat flexible and nonfluorescent; H(Mohs) 3–4; D(calc.) 3.41 for the idealized formula; uniaxial negative, ω = 1.803(3), ɛ = 1.581 (calc.). Averaged electron-microprobe analyses yielded CuO 24.71, FeO 6.86, MgO 6.19, ZnO 0.45, TeO3 36.94, H2O (calc.) [21.55], total [96.70] wt.%, leading to the empirical formula based on O = 12. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centered at 3253 cm−1 and a H-O-H flexing frequency centered at 1670 cm−l. The mineral name honours Joseph F. Leising, Reno, Nevada, who helped collect the discovery specimens.
Coesite from quartz-jadeitite in the Dabie Mountains, Eastern China
Authors: Su Wen , Xu Shutong , Jiang Laili , Liu Yican
Published: December 2006

The Dabie Mountains is a collisional orogen between the North China and Yantze Continental plates. It is composed, from south to north, of the foreland fold and thrust belt alternated with molasse basin, the subducted cover and basement of the Yangtze continental plate, the meta-ophiolitic melange belt, the forearc meta-flysch nappe (bounded by southward and northward thrust belts) in which there may be a buried volcanic arc and a relict back-arc basin (Fig. 1A) (Xu et al., 1992a, 1994).
The presence of vaterite in bonding mortars of marble inlays from Florence Cathedral
Authors: Signorelli S. , Peroni C. , Camaiti M. , Fratini F.
Published: December 2006

During the study of some decay processes in marble covering the façade of the Florence Cathedral (1870-1887), vaterite was found as the principal component of some bonding mortars of inlay decorations.

Vaterite is one of the three polymorphous phases of CaCO3 and crystallizes in the hexagonal system, dihexagonal bipyramidal class (Kamhi, 1963; Sato and Matsuda, 1969): it is unstable under normal environmental conditions (Deer et al., 1964).
The phosphate mineral association of the granitic pegmatites of the Fregeneda area (Salamanca, Spain)
Authors: Roda E. , Fontan F. , Pesquera A. , Velasco F.
Published: December 2006

In the Fregeneda area different pegmatitic types can be distinguished on the basis of their mineralogy, internal structure and field relationships. The most common type corresponds with simple pegmatites with a homogeneous internal structure, but Li and Sn-bearing pegmatites are also relatively widespread, besides a minority group of Fe-Mn phosphate-bearing pegmatites that has recently been characterized. These pegmatites are located in an intermediate zone, between the barren pegmatites and the most evolved Li and Sn-bearing bodies, and they carry a complex association of phosphate minerals. The study of these phosphates has allowed the identification of the primary phases as wyllieite, graftonite, sarcopside, triplite-zwieselite and ferrisicklerite; the secondary phosphates are rosemaryite, heterosite-purpurite, alluaudite and väyrynenite. In this study, the main characteristics of these phosphate minerals are reported, including their chemical composition, analysed by electron microprobe, and their unit-cell parameters, calculated using X-ray powder diffraction techniques.

A common transformation mechanism in this phosphate association is the oxidation of the transition metal cations at the same time as Na-leaching in wyllieite to generate rosemaryite, and Li-leaching in ferrisicklerite to generate heterosite. The occurrence of sarcopside lamellae in ferrisicklerite and heterosite is evidence of the replacement processes of the former by the latter. A Na-metasomatic replacement of the early phosphates as ferrisicklerite and graftonite, producing alluaudite, is also a well developed process.

Phosphate minerals occur in pegmatites with an intermediate degree of fractionation, appearing between the barren and the more evolved pegmatites with Li and Sn, which is in agreement with the pegmatite field zonation established in the literature.
Compositional segregation and solid solution in the lead-dominant alunite-type minerals from Broken Hill, N.S.W.
Authors: Rattray K. J. , Taylor M. R. , Bevan D. J. M. , Pring A.
Published: December 2006

A study of the composition and unit cell data of a suite of lead-rich minerals of the alunite-jarosite group from the oxidized zone of the ore body at Broken Hill, New South Wales, Australia, has revealed almost complete XO4 (X = As, P, S) solid solution in these minerals at this deposit. The species in the group noted are hidalgoite, hinsdalite, beudantite, segnitite and plumbogummite. These minerals at Broken Hill exhibit a number of growth textures, including oscillatory zoning, colloform banding and replacements. Zoning in these minerals is due to the segregation of Al- and Fe-rich members, and compositions indicate a strong coupling of Fe3+ with and Al with
The crystal structure of carminite: refinement and bond valence calculations
Authors: Kharisun  , Taylor Max R. , Bevan D. J. M , Pring Allan
Published: December 2006

The crystal structure of carminite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is orthorhombic, Cccm with a = 16.591(2), b = 7.580(1), c = 12.285(1) Å, Z = 8; the structure has been refined to a conventional R = 3.3% using 913 observed reflections [I>2σ(I)]. The structure contains stepped chains of edge-sharing pairs of Fe(O,OH)6 octahedra; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations.
Cu and Zn ordering in aurichalcite
Authors: Charnock J. M. , Schofield P. F. , Henderson C. M. B. , Cressey G. , Cressey B. A.
Published: December 2006

The advantages of X-ray absorption spectroscopy have been utilized to assess the Cu and Zn ordering in aurichalcite, (Cu5−xZnx)(OH)6(CO3)2. We have examined one hydrozincite sample and three aurichalcite samples in which the Cu:Zn ratios are in the range 1:3 to 2:3. Copper 2p XAS confirms that there is no monovalent copper in aurichalcite and that in each sample the copper might be distributed across more than one metal site. EXAFS, at the Cu and Zn K-edges, shows that the copper atoms preferentially enter the Jahn-Teller elongated, octahedral (M2) and trigonal bipyramidal (M4) sites, with the zinc atoms entering the more regular octahedral (M1) and tetrahedral (M3) site. Substantial solid solution towards the zinc rich region is facilitated by the substitution of copper by zinc on the M2 and M4 sites. This information, not easily obtained by X-ray diffraction, substantially enhances the understanding of the structure of aurichalcite.
Possible constraints on anatectic melt residence times from accessory mineral dissolution rates: an example from Himalayan leucogranites
Authors: Ayres Michael , Harris Nigel , Vance Derek
Published: December 2006

The concentrations of LREE and Zr in a granitic melt formed by anatexis of a metapelitic protolith will be buffered by the stability of monazite and zircon respectively. The rate at which equilibrium is reached between dissolving monazite and zircon and a static melt is limited by the rate at which Zr and LREE can diffuse away from dissolution sites. If melt extraction rates exceed the rates at which the LREE and Zr in the melt become homogenized by diffusion, extracted melts will be undersaturated with respect to these elements. Evidence from accessory phase thermometry suggests that for many Himalayan leucogranites generated by crustal anatexis, the melts equilibrated with restitic monazite and zircon prior to extraction. In contrast, discordant temperatures determined from accessory phase thermometry suggest that tourmaline leucogranites from the Zanskar region of NW India did not equilibrate prior to extraction. Quantitative interpretation of this discordance assumes that the melt was static prior to extraction, and that accessory phase inheritance was minimal. Modelling of the time-dependant homogenization process suggests that tourmaline leucogranites generated at 700°C probably remained in contact with restitic monazite in the protolith for less than 7 ka and certainly less than 50 ka. Such rapid extraction rates suggest that deformation-driven mechanisms were important in removing these melts from their source.
Unit cell refinement from powder diffraction data: the use of regression diagnostics
Authors: Holland T. J. B. , Redfern S. A. T.
Published: December 2006

We discuss the use of regression diagnostics combined with nonlinear least-squares to refine cell parameters from powder diffraction data, presenting a method which minimizes residuals in the experimentally-determined quantity (usually 2θhkl or energy, Ehkl). Regression diagnostics, particularly deletion diagnostics, are invaluable in detection of outliers and influential data which could be deleterious to the regressed results. The usual practice of simple inspection of calculated residuals alone often fails to detect the seriously deleterious outliers in a dataset, because bare residuals provide no information on the leverage (sensitivity) of the datum concerned. The regression diagnostics which predict the change expected in each cell constant upon deletion of each observation (hkl reflection) are particularly valuable in assessing the sensitivity of the calculated results to individual reflections. A new computer program, implementing nonlinear regression methods and providing the diagnostic output, is described.
Jentschite (TIPbAs2SbS6) – a new sulphosalt mineral from Lengenbach, Binntal (Switzerland)
Authors: Graeser Stefan , Edenharter Andreas
Published: December 2006

Jentschite, TlPbAs2SbS6, is a new sulphosalt mineral from the famous Lengenbach locality (Binntal, Switzerland). It was discovered in association with numerous other Tl-As-sulphosalts such as hutchinsonite, wallisite-hatchite, edenharterite, bernardite, abundant realgar and orpiment in small cavities in a dolomitic rock of Triassic age which forms part of the Penninic Monte-Leone-nappe. The first specimens consisted of extremely small polysynthetically twinned crystals; a later find yielded less complicated twinned crystals in sizes up to 2 mm length. Single crystal X-ray diffraction studies gave a monoclinic cell with a = 8.121(3), b = 23.969(9), c = 5.847(3) Å, β = 107.68(3)° V = 1084.3(5) Å3, Z = 4, space group P21/n. The strongest lines in the X-ray powder diagram are (dobs in Å, Iobs, hkl): 2.823 (100)(116), 3.587 (86)(221), 2.778 (84)(260), 3.998 (74)(060), 2.670 (58)(301), 3.816 (54)(210). Chemical composition (electron microprobe, mean of 15 analyses, wt.%) is: Tl 23.92, Pb 21.44, As 19.16, Sb 12.53, S 22.42, total 99.47 wt.% from which a simplified formula TlPbAs2Sb1S6 can be derived. This formula is very close to that of the (orthorhombic) mineral edenharterite TlPbAs3S6. From structural and chemical data it was interpreted as the ordered structure of an Sb-bearing relative of edenharterite, a postulation that meanwhile could be confirmed by the complete structure determinations of both, edenharterite and jentschite (Berlepsch, 1996). Jentschite occurs in prismatic crystals up to 2 mm length; it is opaque with a black metallic to submetallic luster, red translucent in thin fragments. Fracture is uneven to conchoidal, the mineral is extremely brittle, the cleavage along (01) is perfect; the streak is dark red (darker than that of edenharterite). Mohs hardness is 2–2½, according to a microhardness VHN (10 g load) of 38–51 kg/mm2. The calculated density yields Dcalc = 5.24 g/cm3.

The name is for Franz Jentsch (1868–1908) from Binn, a local ‘Strahler’ and for several years head of an early Lengenbach syndicate that exploited the rare Lengenbach sulphosalt minerals at the beginning of this century.
Mineralogical norm calculations applied to tropical weathering profiles
Authors: Voicu G. , Bardoux M. , Voicu D.
Published: December 2006

In contrast with igneous and metamorphic rocks, classical petrochemical calculation methods cannot be used for tropical weathering components (saprolite, bauxitic, ferruginous, siliceous and calcareous laterite) in converting whole-rock chemical analyses into normative mineralogical weight percentages. Weathering profiles are characterized by a mixture of primary and secondary minerals, which are not considered in the classical methods of mineralogical norm calculation. A new petrochemical calculation algorithm is proposed for the conversion of whole-rock chemical analyses into weathering norm (WN) for several components of the tropical weathering profiles. The normative minerals are represented by three primary minerals, six secondary minerals, four primary/secondary mineral pairs, and five minerals which can have both primary and secondary origin. This algorithm has been used in MINNOR, a WINDOWS application written in Visual Basic, which calculates the mineralogical norm. In order to test the program, several types of different chemical weathering profiles from South America and Africa have been selected. Special attention is paid to the weathering profile from Omai, Guyana, South America.
Ilmenite from the Chavara deposit, India: a critical evaluation
Authors: Ramakrishnan C. , Mani R. , Suresh Babu D. S.
Published: December 2006

The mineralogical status of ilmenite from a prominent modern placer deposit of India is illustrated using different techniques. Compositional, powder XRD, TGA and SEM analyses prove that consistent low temperature alteration took place in Chavara ilmenite leading to the formation of a pseudorutile-hydrated-ilmenite stage. Except for the indication of a geochemical zonation at the southern tip of the deposit, the Chavara ilmenite points to a common origin throughout its 22 km stretch along the coast. We advocate a major segregation activity by marine factors to the accumulated sediments in the shelf zone in order to originate such a huge deposit of homogeneous composition.
The vibrational spectra of BaMg(CO3)2 (norsethite)
Authors: Böttcher Michael E. , Gehlken Peer-Lennart , Skogby Henrik , Reutel Christian
Published: December 2006

The FTIR spectra of synthetic BaMg(CO3)2 (norsethite) are measured at ambient temperature and atmospheric pressure, and the influence of formation conditions on the FTIR spectra is investigated. The results are compared with those for natural norsethite from Långban (Sweden) and Rosh Pinah (Namibia). The Raman spectrum of synthetic norsethite is reported, too. A number of first-order internal modes of the carbonate ion group (ν1, ν2, ν3, ν4) are found to be infrared and Raman active. Additonally, the (ν1+ν3) and (ν1+ν4) combination modes and the (2*ν2) overtone are observed in the FTIR and Raman spectrum, respectively. The carbon isotopic-shift coefficient for ν2 due to the substitution of 12C by 13C (ν2(13CO32-)/ν2(12CO32-) = 0.971 ± 0.002), observed by FTIR spectroscopy, agrees with the theoretical value of 0.969.
Feinglosite, a new mineral related to brackebuschite, from Tsumeb, Namibia
Authors: Clark A. M. , Criddle A. J. , Roberts A. C. , Bonardi M. , Moffatt E. A.
Published: December 2006

Feinglosite, the zinc analogue of arsenbrackebuschite, was found lining a cavity in a sample of massive chalcocite from Tsumeb, Namibia. In this cavity it is associated with wulfenite, anglesite and goethite. The mean of seven electron-microprobe analyses (wt.%) is: PbO 61.4, ZnO 7.3, FeO 1.8, As2O5 22.1, SO3 5.3, H2O (by difference) [2.1], total = [100.00]%, leading to the ideal formula: Pb2(Zn,Fe)[(As,S)O4]·H2O. Feinglosite is monoclinic, space group P21 or P21/m, a 8.973(6), b 5.955(3), c 7.766(6) Å, β 112.20(6)°, with Z = 2. The strongest five reflections of the X-ray powder diffraction pattern are [d in Å (I) (hkl)]: 4.85 (50) (110), 3.246 (100) (112), 2.988 (60) (301), 2.769 (60) (300/211), 2.107 (50) (321). The mineral is pale olive-green, transparent, sectile, and has a white streak and adamantine lustre. It overgrows clusters of goethite crystals and forms globular microcrystalline aggregates up to 0.5–0.75mm in size. The hardness on Mohs' scale is 4–5: the mean micro-indentation hardness is 263 at VHN100. Its calculated density is 6.52 g cm−3. The mineral is pale brownish grey in reflected light (when compared with goethite). Visible spectrum reflectance data are presented. Feinglosite is named for Mark N. Feinglos who first recognised the mineral on a specimen in his collection.
Cognate gabbroic xenoliths from a tholeiitic subvolcanic sill complex: Implications for fractional crystallization and crustal contamination processes
Authors: Preston R. J. , Bell B. R.
Published: December 2006

Intruded into the Palaeogene lava field and underlying Moine (Neoproterozoic) crystalline basement rocks around Loch Scridain, Isle of Mull, Scotland, is a suite of high-level, inclined, xenolithic sheets, ranging in composition from basalt, through andesite and dacite, to rhyolite. These sheets, associated with the Mull central volcano, were emplaced post 55 Ma. As well as numerous crustal xenoliths, the more basic members of the complex contain a diverse suite of ultrabasic and basic xenoliths. Xenolith types include feldspathic peridotite with cumulus olivine, pyroxenite, gabbro with cumulus plagioclase and cumulus clinopyroxene, and pure anorthosite. Mineralogical data, coupled with whole-rock major- and trace-element data from a small number of the xenoliths suggest that the xenoliths represent early-formed cumulates cognate with their host basalts. Sr and Nd isotope data from the xenoliths confirms the cognate origin, and also shows that the basic magmas suffered crustal contamination at an early stage.
Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif
Authors: Murciego A. , Garcla Sanchez A. , Dusausoy Y. , Martin Pozas J. M. , Ruck R.
Published: December 2006

This paper is based on microprobe analysis (Ta, Nb, Fe, Mn, Ti, W, Sn) and Fe3+ EPR spectra of cassiterite samples from 14 tin deposits from the Iberian Hercynian Massif. The interpretation of microprobe data, atomic ratios (Fe+Mn)/(Nb+Ta), and Fe3+ EPR spectra reveal that the coupled substitution: 3Sn4+ = (Fe,Mn)2+ + 2(Nb,Ta)5+ is dominant in cassiterites from pegmatites, and high-temperature quartz veins and in the dark zones of cassiterites.

The mechanisms:

2Sn4+ = Fe3+ + (Nb,Ta)5+ and

Sn4+ + O2− = Fe3+ + OH−

are dominant in those from medium-low temperature quartz veins and in the light zones of cassiterites.