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AbstractOrtho- and clinopyroxenes within partially-hydrated harzburgites from Elba and Val di Cecina (Italy) show lamellar exsolution textures and variable replacement by biopyriboles, talc-chlorite-serpentine mixed layers and serpentine. Chemical and geothermometric data suggest that the pyroxenes crystallized at 1240–1051°C, followed by subsolidus exsolution at slightly lower T(1145–1025°C for clinopyroxene lamellae + orthopyroxene matrix pairs and a 1033–982°C range for orthopyroxene lamellae + clinopyroxene matrix pairs).Investigation by transmission electron microscopy of exsolved enstatite and augite reveals a multistage hydration process. The first stage (highest T, probably in the amphibole stability field) leads to the formation of biopyribole lamellae within exsolved augite, leaving the enstatite matrix unaffected. The second stage (~500–300°C) corresponds to the topotactic replacement of enstatite by layer silicates (talc + chlorite + serpentine, with (001)layer silicatesparallel to (100)enstatite). Enstatite is also replaced by randomly oriented, poorly crystalline serpentine. The last hydration stage (<300°C) corresponds to the disappearence of augite and recrystallization of serpentine, leading to completely hydrated bastites with random lizardite lamellae, polygonal serpentine and minor chrysotile.

Chloritized annite from the Irizar granite has been used for laser-heating experiments, following the procedures used for 40Ar– 39Ar dating (heating steps in the 600–1080 °C temperature range). Four runs, at different temperatures, have been characterized using transmission electron microscopy, electron diffraction, micro-Raman and micro-IR spectroscopies. The water loss was evaluated by thermogravimetry. The chlorite domains break down first forming (001) amorphous layers, that later coalesce to rounded, equant inclusions and finally recrystallize to olivine and spinels plus silica glass. These phases occur within negative crystals hosted in ordered dehydrated annite, produced by dehydration and annealing of the starting annite. Dehydrated annite, olivine and spinels display topotactic relationships, determined by the common orientation of closely packed oxygen layers.

Pyroxenes of pigeonitic and augitic bulk compositions in H3–4 chondritic meteorites commonly exhibit sigmoidal precipitates, rather than the elsewhere common lamellar associations. Most often, submicrometric sigmoids with calcic clinopyroxene composition occur within clinoenstatite; more rarely, clinoenstatite sigmoids occur within calcic clinopyroxene. The sigmoids appear as ‘001’ terminated lamellae, with terminations rotated in opposite directions towards the ‘100’ orientation. Pre-exsolution pigeonite and augite formed at temperatures higher than 980 °C, whereas sigmoidal exsolution occurred between 990 and 830 °C. Local anomalous lattice parameters determined by electron diffraction suggest that lattice parameters are most strained where the exsolution texture is most poorly defined. Shear strain occurs during exsolution due to mismatching lattice parameters and variable ß angles. In response to shear stress, the lamellae relax and assume sigmoidal strained morphologies. Sigmoidal exsolution is strongly controlled by (100) orthoenstatite stacking faults that possibly trigger exsolution.

Abstract—Sixteen texturally different (porphyritic, barred, radial, cryptocrystalline) FeO‐rich chondrules from the unequilibrated ordinary chondrites Brownfield, Frontier Mountain (FRO) 90003 and FRO 90032 were characterized by optical and scanning electron microscopy and then thoroughly studied by transmission and analytical electron microscopy. Nanotextural and nanochemical data indicate similar thermal evolution for chondrules of the same textural groups; minor, yet meaningful differences occur among the different groups. Olivine is the earliest phase formed and crystallizes between 1500 and 1400 °C. Protoenstatite crystallizes at temperatures higher than 1350–1200 °C; it later inverts to clinoenstatite in the 1250–1200 °C range. Enstatite is surrounded by pigeonitic or (less frequently) augitic rims; the minimal crystallization temperature for the rims is 1000 °C; high pigeonite later inverts to low pigeonite, between 935 and 845 °C. The outer pigeonitic or augitic rims are constantly exsolved, producing sigmoidal augite or enstatite precipitates; sigmoidal precipitates record exsolution temperatures between 1000 and 640 °C. Cooling rate (determined using the speedometer based upon ortho‐clinoenstatite intergrowth) was in the order of 50–3000 °C/h at the clinoenstatite‐orthoenstatite transition temperature (close to 1250–1200 °C), but decreased to 5–10 °C/h or slower at the exsolution temperature (between 1000 and 650 °C), thus revealing nonlinear cooling paths. Nanoscale observations indicate that the individual chondrules formed and cooled separately from 1500 °C down to at least 650 °C. Accretion into chondritic parent body occurred at temperatures lower than 650 °C.

The polymetallic mineralisation of the Kutná Hora ore district (Czech Republic) has been successfully exploited for silver production, specially during the 14th and 15th centuries. Five slags, sampled from the Vrbovy mlýn smelting centre, have been analysed by X-ray fluorescence spectrometry, X-ray powder diffraction, optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. The slags are mostly composed of SiO2, FeO, CaO and minor amounts of Al2O3; important sulphur and zinc contents were detected. Depending on the calcium content, two main pyrometallurgical phase assemblages were identified, i.e., ferrobustamite + hedenbergite vs. hedenbergite + fayalite. Crystalline phases and glassy matrix contain relevant amounts of zinc. The charge ore underwent only a mild roasting prior to smelting, as indicated by the relevant sulphur content. All the slags were obtained at temperatures ranging from 1150 °C to 1300 °C, using appropriate silica fluxes to optimise metal yield. Due to higher viscosity, massive matte may occur in the slags, with limited silver content. The Kutná Hora slags, when compared with previous studies from Italian smelting sites, show similarities in metallurgical techniques.

Abstract—La Villa is an unshocked H4 chondrite. Chemical compositions require crystallization at temperatures >1250 °C for enstatite and >1211 °C for augite. Widespread (100) polysynthetic twins and (001) contraction cracks in enstatite indicate crystallization as protoenstatite, inverted to either ortho‐ or clinoenstatite or both on cooling. High‐resolution transmission electron microscopy shows a range of ortho‐clinoenstatite intergrowths: heavily faulted clinoenstatite in radial and poikilitic chondrules, almost regular orthoenstatite in a microgranular chondrule and in the matrix. In the former, the clinoenstatite lamellae are both even or odd multiples of the 9Å periodicity, a few unit cells thick, twinned and interleaved with minor orthoenstatite. In the latter, orthoenstatite lamellae are regularly stacked for more than 2000 Å. Localized annealing effects, reversing clinoenstatite to orthoenstatite, are revealed by “U‐shaped” and “Z‐shaped” terminations. The variable microstructures suggest different cooling rates for the different chondrule types, soon after the liquidus‐to‐solidus transition (1200 to 1300 °C) but prior to accretion. In particular, clinoenstatite‐rich crystals from radial and poikilitic chondrules give cooling rates on the order of 100 and 10 °C/h. Comparisons with previous works on dynamic crystallization experiments and orthopyroxene Fe‐Mg cation ordering indicate a nonlinear cooling path from the high chondrule formation temperatures to a postaccretionary low‐temperature (340–480 °C) evolution.

Sudoite, the di-trioctahedral chlorite with ideal composition (Mg2Al)(Al2)(Si3Al)O10(OH)8 is a widespread rock-forming mineral in meta-siltstones and psammites of the Verrucano sequence of the Northern Apennines. Sub-ellipsoidal aggregates, probably derived from muscovite clasts, consisting of sudoite, pyrophyllite and muscovite, are common; sudoite may also occur as thin blades in the rock matrix. The co-existence of sudoite, Ferich chloritoid and pyrophyllite, reported here for the first time, has been observed in specimens from the M. Argentario and Monticiano-Roccastrada areas. This three-phase assemblage, diagnostic of a specific metamorphic facies, may be a tool for detailed zonation of low-grade terranes.

Based on coexisting rolled chrysotile and polygonal serpentine fibers with 15 or 30 sectors each, a crystallographic model for polygonization of chrysotile is proposed. It is based on an assumed chrysotile-to-lizardite transition. Polygonization of chrysotile requires more likely 15 partial dislocations per turn, as required by polytype translational operators for serpentines. The observed number of sectors corresponds to the two most elastically stable arrays of dislocations. Homogeneous shear of the layer stacking arising from intersector kinking results in a cyclic distribution of twins and/or different polytypes. This makes the fiber axis a fivefold symmetry axis and consequently polygonal serpentine and chrysotile to be both forms of serpentine with local fivefold symmetry. This model is alternative to the recent crystallograpic model by Chisholm (1991, 1992).

Sursassite is monoclinic, space group P21/m, a=8.70, b=5.79, c=9.78 Å, ß=108.9°. The crystal structure was determined with X-rays and refined to R=0.065, obtaining Mn2Al3[(OH)3(SiO4)(Si2O7)] as ideal crystal chemical formula. Sursassite, isostructural with macfallite Ca2Mn3[(OH)3(SiO4)(Si2O7)], is closely related to pumpellyite Ca2Al3[(OH)3(SiO4)(Si2O7)]. In fact both sursassite and pumpellyite, apart from the different chemical composition, are built up by common structural layers, which are repeated by different stacking vectors. As a result, faulted stacking sequences are energetically possible.

Abstract—iron‐magnesium ordering was determined in orthopyroxenes from two suites of unshocked (shock stage S1, S2), equilibrated L‐ and LL‐chondrites (10 grains from 5 meteorites and 7 grains from 4 meteorites, respectively) by means of single crystal x‐ray diffraction (SCXRD). This study, together with a previous investigation of H‐chondrites (13 grains from 8 meteorites), produces an internally consistent data set about the thermal record in equilibrated ordinary chondrites (EOCs).

Chlorite-muscovite porphyroblasts occur in the low-grade metapelites from Nurra (NW Sardinia). Although actually heterogeneous and built up by two different intermixed minerals, the porphyroblasts strongly simulate optical homogeneity and produce microprobe analyses that are typical for metamorphic vermiculite. Transmission and scanning electron microscopy, combined with analytical facilities, leads to a deeper characterization of the porphyroblasts, that actually consist of a random association of chlorite and muscovite.

Abstract: A well crystallized and homogeneous specimen of lizardite from Monte Fico, Elba, Italy, has been studied by Mössbauer and Fourier transform infrared (FTIR) spectrometries. One of the aims was the determination of the oxidation state and the distribution of iron in the structure of this reference sample. Mössbauer data indicate the presence of octahedral ferrous iron, octahedral ferric iron and tetrahedral ferric iron (59.9, 31.3 and 8.8% of total iron, respectively). The existence of only one octahedral site, previously suggested by X-ray structure refinement, is confirmed. The occurrence of tetrahedrally coordinated iron is indicated also by FTIR spectrometry, in particular by the presence of an absorption band at 790 cm–1. Based also on new electron microprobe data, the improved crystal chemical formula for lizardite from Monte Fico is: (Mg2.74Fe2+0.10Fe3+0.05Al0.11)Σ=3.00 · (Si1.94Al0.05Fe3+0.01)Σ=2.00O5.05(OH)3.95.

The structure of lizardite-1T from Monte Fico, Elba, was refined in space group P31m using neutron diffraction data, measured at 8, 150, and 294 K, and full-profile Rietveld refinement techniques. The lattice parameters at 8 K [a = 5.3267(2), c = 7.2539(6) Å], 150 K [a = 5.3260(2), c = 7.2574(6) Å], and 294 K [a = 5.3332(2), c = 7.2718(6) Å] show nonlinear expansion, with nearly all volume change above 150 K. H positions were precisely refined at 8 K. The inner H4 atom deviates from the idealized O,O,z positions and is disordered over three symmetry-related positions 0.24 Å away from the ternary axis. The outer H3 atom location is consistent with the previous single-crystal X-ray structure refinement. On the basis of the present thermal expansion data and previous compressibility measurements, the following equation of state for lizardite-1T is proposed: VP,T= V0[1 + 32.8 × 10-6(T - 294) - 15.5 × 10-4(P - 0.001)]. Accordingly, the constant volume condition requires geothermal gradients on the order of 15 °C/km.

Summary Niocalite (monoclinicPa, a=10.863(3),b=10.431(3),c=7.370(2) Å, ß=110.1(1)°) belongs to the cuspidine group. Its crystal structure has been refined toR1=0.069 andRw=0.046, using 2411 independent reflections. Niocalite is isostructural with cuspidine and lavenite, but topologically distinct from the related mineral wöhlerite.

Summary The crystal structure of låvenite (monoclinicP21/a,a=10.83(1),b=9.98(1),c=7.174(5) Å, ß=108.1(1)o), was refined using 1743 independent reflections toR=0.032 andRw=0.036. The refined structure is in agreement with the structure model proposed bySimonov andBelov (1960), characterized by the presence of walls of large cation polyhedra. These walls are four columns large, linked together by both direct connection as well as by Si2O7 groups. The cation distribution inside the wall is explained and compared with that found in other phase of the cuspidine group. The crystal chemical formula resulting from structural and chemical analyses on låvenite from Langesund (Norway) is (Na6.50Ca1.47Y0.03) (Ca0.93 Mn1.26Fe0.872+Ti0.65Zr0.18Mg0.05) (Zr3.42Nb0.58) (Si2O7)4O3.82F3.98.

The systematic study of both natural and synthetic clinopyroxenes often indicates the presence in the difference Fourier map of a maximum of residual density of up to 0.8 electrons, here labelledM2', close to theM2 site along the diad axis, defining a square pyramid co-ordination polyhedron. To investigate the nature and the crystalchemical implications of this feature, a limited but representative set of clinopyroxenes of volcanic, metamorphic and synthetic origin has been investigated by X-ray structure refinement (at 0.7 and 0.4 Å resolution), by microprobe analysis and by transmission electron microscopy. The most important results are: a) at increasing resolution, the height of theM2' peak increases while its co-ordinates move towardM2; b) as (Ca + Na) content approaches 1.0 atom per formula unit,M2' vanishes; c)M2' has been found in clinopyroxenes which show differing incipient exsolution microstructures, from spinodal decomposition to non-periodic fluctuations, as well as in homogeneous specimens. The presence ofM2' is interpreted in terms of the simultaneous coexistence in the crystals of two different structural models, approximately diopside and clinoenstatite. An accurate evaluation of the totalM2 + M2' site occupancy is strongly suggested in XREF work, particularly when thermodynamic and kinetic considerations have to be obtained with accurate determinations of site occupancy factors as a starting point.

The Rex protein of human T-cell leukemia virus type I (HTLV-I) was expressed in bacteria and partially purified. Rex was shown to bind in vitro specifically to an RNA sequence located in the 3' long terminal repeat of HTLV-I, named Rex-responsive element (RXRE). Rex also bound in vitro to the human immunodeficiency virus type 1 (HIV-1) Rev-responsive element (RRE), while purified HIV-1 Rev protein did not bind to the RXRE. The binding results obtained in vitro are therefore in agreement with the nonreciprocal function of Rev and Rex in vivo. Rex binds specifically to both RRE and RXRE and activates expression in both HIV-1 and HTLV-I, while Rev binds to RRE and activates only HIV-1. Binding of Rex to RRE deletion mutants previously shown to lack either the Rev-responsive or the Rex-responsive portion suggested preferential binding of Rex to a distinct target within the RRE. These results demonstrated that Rex, like Rev, acts by binding to a specific RNA target.

Neurofibrillary tangles (NFT), one of the neurodegenerative features of Alzheimer's disease, Down's syndrome and normal aging, is a constant, widespread neuropathological finding in Guamanian amyotrophic lateral sclerosis (ALS), parkinsonism-dementia (PD) and in neurologically normal Guamanians, dying of causes other than ALS and PD. NFT in brain tissue sections of patients with Guamanian ALS and PD were immunoreactive to antibodies directed against a 43-amino acid synthetic peptide homologous to amyloid ß/A4-protein (anti-SP43) associated with Alzheimer's disease. NFT extracted from frozen brain tissues of Guamanian patients with ALS and PD and from tissues of neurologically normal Guamanians were congophilic and birefringent. By negative-stain electron microscopy, NFT preparations contained bundles and/or isolated single, straight, unpaired filaments in Guamanian AlS and occasionally pairing of filaments in neurologically normal Guamanians, measuring 5–20 nm in diameter. Formic acid digestion of NFT preparations, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion high-pressure liquid chromatography, showed a protein with an apparent molecular mass of 4-to 4.5-kDa, which by Western blot analysis was immunoreactive to anti-SP43. Immunoabsorption of purified NFT or SP43 with anti-SP43 abolished immunostaining. Our study corroborate previous data that amyloid ß/A4-protein is present in NFT in Guamanian PD. Furthermore, our data indicate that amyloid ß/A4-protein is present in NFT in brain tissues of patients with Guamanian ALS and in neurologically normal Gumananians, suggesting a common mechanism of amyloidogenesis with NFT formation in Alzheimer's disease and normal brain aging.

AbstractTitanian aegirine in a pegmatoid differentiate from leucitite sensu stricto(i.e. without modal plagioclase) was found to contain significant K (up to 0.07K atoms per formula unit; 0.11 wt.% K2O) by electron probe microanalysis. A transmission electron microscope study showed that this pyroxene contained a lamellar amorphous phase and other more irregular, amorphous domains where K and Al are concentrated. The microstructures suggest that the aegirine-amorphous phase system did not achieve textural equilibrium. Also, the chemistry of this phase is variable, particularly in Ca and Mg, suggesting lack of chemical equilibrium within the liquid from which the phase derived. The average composition of the latter approaches that of the coexisting K-richterite and is interpreted as trapped residual liquid, i.e. glass, from pyroxene crystallization which failed to develop a crystalline amphibole. In view of the extensive stability of richterite coexisting with pyroxene to high pressure, the reported occurrence of ‘K-bearing pyroxene’ may not be considered as a homogeneous K-bearing phase and a predictable potassium carrier in the petrogenesis of K-rich rocks like leucitites and lamproites.

The crystal structure of wöhlerite (monoclinicP21,a=10.823(3,b=10.244(3),c=7.290(2) Å, β=109.00(4)o) was refined using 2343 independent diffractions toR1=0.019 andR2=0.025. The refinement confirms the main features of the structure model proposed byShibayevaandBelov(1962), namely the walls of large cation polyhedra interconnected as in cuspidine, with Si2O7groups linked to the polyhedra. At difference from the structure proposed by the quoted authors, both the Si2O7groups are clinging to edges of calcium polyhedra. The cation distribution in the polyhedral walls and the location of fluorine anions are clarified and discussed, resulting in the following crystal chemical formula Na4(Ca7.48Mn0.20Fe0.32)Zr2(Nb1.6Ti0.4) (Si2O7)4O4F2(O1.6F0.4). Die Kristallstruktur des Wöhlerits (monoklinP21,a0=10,823(3),b0=10,244(3),c0=7,290(2) Å, β=109,00(4)o) wurde mit 2343 unabhängigen Reflexen aufR1=0,019 undR2=0,025 verfeinert. Die Verfeinerung bestätigt im wesentlichen Züge des vonShibayevaundBelov(1962) vorgeschlagenen Strukturmodells, nämlich Bänder aus den Polyedern um die großen Kationen, die — wie im Cuspidin — durch an den Polyedern hängenden Si2O7-Gruppen verknüpft sind. Die Kationenverteilung in den Polyederbändern und die Lokalisation der Fluor-Anionen wurden aufgeklärt und werden diskutiert; es ergibt sich folgende kristallchemische Formel Na4(Ca7,48Mn0,20Fe0,32)(Zr2(Nb1,6Ti0,4) (Si2O7)4O4F2(O1,6F0,4).