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We investigated the oxidation behaviour of a synthetic potassic-ferro-richterite up to 750 degrees C by using simultaneous X-ray absorption spectroscopy and X-ray diffraction experiments with synchrotron radiation. From the X-ray diffraction results, we observed an abrupt decrease of cell dimensions at approximate to 335 degrees C accompanied by an anomalous increase in the monoclinic cell angle . From the analysis of the XANES spectra at the iron K-edge, we observed that the structural shrinkage is due to the iron oxidation process, coupled to hydrogen loss, occurring at approximate to 315 degrees C, slightly before the cell contraction. Combining these results with previous studies performed on similar samples by single-crystal structure refinement, Mossbauer, high temperature-Fourier transform IR and Raman spectroscopies, we show that the temperature evolution in Fe-amphiboles is a multi-step process. Following the iron oxidation driven by temperature, the structural dynamics in this double-chain silicate is ruled by local strains in the ribbon of iron-filled octahedra, mainly due to the contraction of the M(1) site.

A second occurrence of ferri-fluoro-leakeite has been identified in the Bratthagen nepheline syenite pegmatite (Vestfold County, Norway). With respect to the holotype found at the Verkhnee Espe deposit (Akjailyautas Mountains, Kazakhstan; Cámaraet al., 2010), it is closer to the ideal composition because of its larger Li and Mg contents and the absence of an oxo-component; however, it has a significant Zn content (0.29 a.p.f.u.). The ideal formula of ferri-fluoro-leakeite isANaBNa2C(Mg2Fe23+Li)TSi8O22WF2and the empirical formula derived from electron-microprobe analysis and single-crystal structure refinement for the sample used here isA(Na0.68K0.32)S=1.00BNa2.00C(Mg1.69Mn0.252+Fe0.242+Zn0.29Al0.23Fe1.503+Ti0.02Li0.78)S=5.00TSi8O22W(F1.59(OH)0.41)S=2.00. Unitcell data area= 9.788(2),b= 17.826(3),c= 5.282(1) Å, β = 104.195(5)°,V= 893.5 (3) Å3,Z= 2. Crystal-chemical analysis shows that Li is ordered at theM(3) site and Zn is ordered mainly at theM(2) site, confirming previous findings for Li-bearing amphiboles. The new data also make quantification of the oxo component in Na amphiboles possible.

Fluoro-potassic-pargasite, ideally AKBCa2C(Mg4Al) (Si6Al2)O22WF2, a new amphibole species, has been found in a skarn in the Tranomaro area, Madgascar. The sample used for the description of the new mineral species is a large single amphibole crystal, 4 mm × 2 mm × 2 cm in size, brownish-black with brownish-yellow phlogopite lamellae adhering to one face of the crystal. Fluoro-potassic-pargasite is brittle, has a Mohs hardness of 6.5 and a splintery fracture; it is non-fluorescent, has perfect {110} cleavage, no observable parting, and has measured and calculated densities of 3.46 and 3.151 g cm−3, respectively. In plane-polarized light, it is pleochroic, X = colourless to very pale grey, Y = very pale grey, Z = colourless; X ^ a = 46.9° (in β obtuse), Y ‖ b, Z ^ c = 31.4° (in β acute). It is biaxial positive, α = 1.638(2), β = 1.641(2), γ = 1.653(2); 2Vobs = 49.6(4)°, 2Vcalc = 53.4°.Fluoro-potassic-pargasite is monoclinic, space group C2/m, a = 9.9104(2), b = 17.9739(4), c = 5.3205(1) Å, β = 105.534(2)°, V = 913.11(6) Å3, Z = 2. The eight strongest lines in the X-ray powder-diffraction pattern are [d in Å(I)(hkl)]: 3.133(100)(310), 3.270(55)(240), 2.809(47)(330). 8.413(45)(110), 2.698(39)(151), 3.374(31)(131), 2.934(29)(221) and 1.647(29)(461). Electron microp-robe analysis gives SiO2 40.20, Al2O3 17.61, TiO2 0.46, FeO 1.96, Fe2O3 2.51, MgO 16.95, MnO 0.05, CaO 13.18, Na2O 0.99, K2O 3.72, F 2.75, H2Ocalc 0.77, sum 99.99 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH + F) = 2 - (2 × Ti), is A(K0.69Na0.28Ca0.04)∑=1.01BCa2.00C(Mg3.64Fe0.242+Mn0.01Al0.79Fe0.273+Ti0.05)∑=5.00T(Si5.80Al2.20)∑=8.00O22W[F1.26(OH)0.74]∑=2.00. The mineral species and name have been approved by the IMA CMNMC (IMA 2009-091).

Fluoro-potassic-magnesio-arfvedsonite, ideally AKBNa2c(Mg4Fe3+)TSi8O22wF2, has been found in a dyke ∼25 km southwest of Monte Metocha, Xixano region, northeastern Mozambique. Fluoro-potassic-magnesio-arfvedsonite and low sanidine form a fine-grained mafic, ultrapotassic, peralkaline igneous rock without visible phenocrysts. The amphibole is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage and no observable parting, and has a calculated density of 3.174 gcm−3. In plane-polarized light, it is pleochroic, X= pale grey-green, Y = blue-green, Z = pale grey; X ^ c = 23.6° (in β obtuse), Y ‖ b, Z ^ c = 66.4° (in β acute). Fluoro-potassic-magnesio-arfvedsonite is biaxial negative, α = 1.652(2), β = 1.658(2), γ = 1.660(2); 2Vobs = 22.5(7)°, 2Vcalc = 30.2°. The unit-cell dimensions are a = 9.9591(4), b = 17.9529(7), c = 5.2867(2) Å, β = 104.340(1)°, V = 919.73(10) Å3, Z = 2. The nine strongest X-ray diffraction lines in the experimental powder pattern are: [d in Å(I)(hkl)]: 2.716(100)(151), 3.410(70)(131), 8.475(50)(110), 3.178(50)(310), 3.309(30)(240), 2.762(20)(31), 2.549(20)(260), 2.351(10)(51), 2.269(10)(331). Electron microprobe analysis gave: SiO2 54.25, A12O3 0.03, TiO2 1.08, FeO 6.69, Fe2O3 8.07, MgO 13.99, MnO 0.32, ZnO 0.05, CaO 1.16, Na2O 6.33, K2O 5.20, F 2.20, H2Ocalc 0.74, sum 99.18 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH+F) = 2−(2 Ti), is AKa0.98B(Na1.18Ca0.18)∑1.99C(Mg3.07Fe0.832+Mn0.04Al0.01Fe0.903+Ti0.12Zn0.01)∑=4.98TSi8O22W[Fi.o3(OH)0.73O0.24]∑2.00 and confirms the usual pattern of cation order in the amphibole structure. The presence of a significant oxo component (locally balanced by Ti at the M(1) site) is related to the crystallization conditions. The presence of Fe3+ at the T sites, originally suggested for the holotype specimen, is discounted for this amphibole composition.

Fluoro-sodic-ferropedrizite, ideally ANaBLi2C()TSi8O22WF2, is a new mineral of the amphibole group from the Sutlug River, Tuva Republic, Russia. It occurs at the endogenic contact of a Li-pegmatite with country rocks near to a diabase dyke and formed by reaction of the pegmatitic melt with the country rock. Fluoro-sodic-ferropedrizite occurs as prismatic to acicular crystals, ranging in length from 0.1–3 cm and widths of up to 50 μm. Crystals occur inparallel to sub-parallel aggregates up to 5 mm across ina matrix of calcite and plagioclase feldspar. Crystals are pale bluish-grey with a greyish-white streak.Fluoro-sodic-ferropedrizite is brittle, has a Mohs hardness of ~6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.116 g cm–3. In plane-polarized light, it is pleochroic, X = pale purple-grey, Y = light grey, Z = colourless; X ^ a = 71.2º (in β acute), Y || b, Z ^ c = 83.4º (in β obtuse). Fluoro-sodic-ferropedrizite is biaxial positive, α = 1.642(1), β = 1.644(1), γ = 1.652(1); 2V(obs) = 68.0(3)º, 2V(calc) = 56.4º. Fluoro-sodic-ferropedrizite is monoclinic, space group C2/m, a = 9.3720(4) Å, b = 17.6312(8) Å, c = 5.2732(3) Å, β = 102.247(4)º, V = 851.5(2) Å3, Z = 2. The strongest ten X-ray diffraction lines in the powder patternare (d in Å ,(I),(hkl)): 8.146,(10),(110); 2.686,(9),(151); 3.008,(8),(310); 4.430,(7),(021); 2.485,(6),(02); 3.383,(4),(131); 2.876,(3),(51, 11); 2.199,(3),(12); 4.030,(2),(111) and 3.795,(2),(31). Analysis by a combination of electron microprobe and crystal-structure refinement gives SiO2 59.81, Al2O3 12.66, TiO2 0.09, FeO 10.32, MgO 5.56, MnO 0.73, ZnO 0.17, CaO 0.20, Na2O 2.81, Li2O 4.80, F 2.43, H2Ocalc 1.10, sum = 99.65 wt.%. The formula unit, calculated on the basis of 24(O,OH,F) is A(Na0.68)B(Li1.92Na0.05Ca0.03)C() T(Si7.98Al0.02)O22W(F1.03OH0.97). Crystal-structure refinement shows Li to be completely ordered at the M(3) and M(4) sites. Fluoro-sodic-ferropedrizite, ideally ANaBLi2C()TSi8O22WF2, is related to the theoretical end-member ‘sodic-pedrizite’, ANaBLi2C(Mg2Al2Li)TSi8O22W(OH)2, by the substitutions CFe2+ → CMg and WF → W(OH).

The crystal structures of eight sodic–calcic and sodic amphiboles from the Kajlidongri manganese mine, India, have been refined to R values of 1–2% using single-crystal Mo K α X-ray data. The crystals used in the collection of the intensity data were subsequently analyzed by electron- and ion-microprobe techniques. Site populations were assigned from the results of site-scattering refinement and stereochemical analysis, taking into account the unit formula determined for each crystal. These amphiboles range in composition from richterite to magnesioriebeckite to magnesio-arfvedsonite. All amphiboles contain Li, which ranges from 0.03 to 0.30 apfu and is completely ordered at the M (3) site. The amount of F in each crystal is equal to twice the amount of Li, suggesting that Li, which is ordered at the M (3) site, is locally associated with F at both the adjacent O(3) sites. The patterns of electron density in the A cavity and the populations at the A , O(3) and M (4) sites are in accord with previously proposed patterns of short-range order in monoclinic amphiboles. The compositions of these amphiboles lie along the join richterite–magnesioriebeckite and show a surprising degree of coherence in their major-element compositions considering the heterogeneity of the host rocks.

The experimental multipole electron density, ρ(r), of diopside was derived from high-resolution single-crystal diffraction at room temperature. Its topological analysis revealed predominantly ionic Si–O bonding, as found in electron density studies of other silicates. In particular, the non-bridging Si–O bonds are slightly less ionic in character than the bridging Si–O bonds. The Ca–O and Mg–O bonds are classified as pure closed-shell ionic interactions. An analysis of –∇2ρ(r) showed the presence of maxima around the oxygen atoms, associated to lone pairs domains that are involved in bonds with the surrounding ions. Calculation of atomic basins gave net charges of –1.56(12), 3.11(17), 1.79(13) and 1.88(18) e for O (averaged), Si, Ca and Mg atoms, respectively. O···O interactions between the O atoms at the vertices of the SiO4 tetrahedron were also detected from the topological analysis of ρ(r), and indicate a cooperative interaction among the lone pairs of neighbouring oxygen atoms. All these results were also confirmed by periodic restricted Hartree–Fock (RHF) calculations.

New experimental amphibole/melt partition coefficients from a variety of geologically relevant amphibole (pargasite, kaersutite, and K-richterite) and melt compositions obtained under conditions of interest to upper-mantle studies are combined with the results of X-ray single-crystal structure refinement. The ideal cation radii (r0), calculated using the lattice-site elastic-strain model of Blundy and Wood (1994) under the hypothesis of complete REE (rare earth elements) ordering at [8]M4, mostly differ significantly from those obtained from both the structure refinement and the ionic radius of [8]Ca2+. Heavier REE may also strongly deviate from the parabolic trends defined by the other REE. On the basis of the crystal-chemical knowledge of major-element site-preference in amphibole and the occurrence of two sites with different co-ordination within the M4 cavity (M4 for Ca and Na, M4′ for Fe2+ and Mg), we propose a new model for REE incorporation. LREE order at the [8]M4 site, whereas HREE prefer the M4′ site with lower co-ordination in amphiboles with a significant cummingtonite component, and may also enter the M2 octahedron, at least in richterite. This more complex model is consistent with the observed Amph/LD, and drops the usual assumption that REE behave as a homogeneous group and order at the M4 site. The availability of multiple crystal-chemical mechanisms for REE3+ incorporation explains why measured and estimated Amph/LDHREE may differ by up to one order of magnitude. When REE enter two different sites within the same cavity, a fit performed on the basis of a single curve may appear correct, but the values obtained for r0 are biased towards those of the dominant site, and the Young's modulus is underestimated. When REE are incorporated in multiple sites in different cavities, the observed pattern cannot be reduced to a single curve, and the partition coefficients of heavy REE would be strongly underestimated by a single-site fit. The simplistic assumption that REE occupy a single site within the amphibole structure can thus substantially bias predictive models based on the elastic-strain theory. Our combined approach allows linkage between fine-scale site preference and the macroscopic properties of minerals and provides more reliable predictive models for mineral/melt partitioning. After the possible site-assignments have been identified, the shape of the Onuma curves constructed from accurately determined Amph/LDREE now allows the active mechanisms for REE incorporation in amphiboles to be recognised even where site populations are not available. The REE preference for polyhedra with smaller size and lower co-ordination than those occupied by Ca invalidates the general idea that Ca acts as a “carrier” for REE.

We applied different independent techniques (electron microprobe analysis, structure reÞ nement, and X-ray absorption spectroscopy) to unravel the possible mechanisms of Sc incorporation in the pyrope-grossular join. Samples were synthesized at elevated pressure and temperature by adding 5 wt% of Sc2O3 to selected nominal compositions (pyrope, pyrope60grossular40, pyrope20grossular80, and grossular). In this way, the site of incorporation was not pre-determined, and only depends on the availability of a mechanism for local charge-balance. The EXAFS spectra of the two end-members could be analyzed by a multi-shell Þ t procedure, whereas the chemical heterogeneity of the Sc-doped solid-solution terms prevented this approach. However, the available information allows detection of different mechanisms of incorporation, which are active as a function of the bulk composition. In pyrope, Sc mainly enters the dodecahedral X site, and the local charge balance is achieved by incorporation of Mg at the adjacent tetrahedral Z site. Local charge-balance requirements suggest that a Z site occupied by Mg bridges two X sites occupied by Sc. When the entrance of Ca provides relaxation of the aver- aged structure, Sc may enter all the three available cation sites via the coupled heterovalent exchange XSc1 ZSc1 XMg–1 ZSi–1 and the homovalent exchange YSc1 YAl–1. In the samples of this work, there is an apparent limit in the Sc incorporation at the Y site, which is in contrast to the favored mechanism of incorporation in Sc-doped andradites. This limit can be explained in terms of relative dimensions of the structural sites when Al is the dominant Y cation. These results must be taken into account when evaluating trace-element behavior in garnets for geochemical purposes. In particular, they explain why DSc can be treated together with DREE in models based on the elastic strain theory in garnets close to the pyrope composition, but deviate from the parabolic Þ t in grossular-rich garnets.

The site location and local geometry of trace amounts (299 ppm) of dysprosium in a natural melanite garnet from a carbonatitic rock have been studied by high-energy fluorescence-detected X-ray absorption fine-structure spectroscopy (XAFS). Measurements were done at the Dy K-edge (53789 eV). Data analysis shows that Dy (i.r. = 0.98 A) is incorporated at the X site, similarly to other REE, namely Nd (i.r. = 1.11 A) and Ce (i.r. = 1.14 A). Comparison of the XAFS data obtained for these three REE and for Ca shows that, within a given garnet composition, the difference in the local geometry can be modelled in terms of differences in the ionic radii. On the contrary, the local coordination of the individual cations is different in distinct garnet compositions, in contrast to what was suggested by previous atomistic simulations of the garnet structure. Comparison of the local coordination geometries available in the literature shows that the Young modulus of the X site strongly depends on the major-element composition of all the structural sites. Both these points are important for Earth Sciences, and especially for geochemical modelling of trace-element incorporation and partitioning.

This special issue of the Mineralogical Magazine springs from the session we organized as part of the Goldschmidt 2013 conference in Florence. The title we proposed “GEOLIFE – Geomaterials for environment, technology and human activities” reflects our feeling that a wise use of the expertise gained by mineralogists while studying the crystal chemistry, as well as the chemical and physical properties of minerals in rocks and soils, still plays an important role in what is called “The cutting edge in Mineralogy and Mineral Physics”. Indeed, the current expertise in the physical, chemical and structural characterization of geomaterials, i.e. minerals, rocks and their synthetic analogues, now allows us to design innovative applications both for technological and environmental purposes. During the meeting we discussed some frontier work on phases produced naturally by the Earth ‘laboratory’ or fabricated within academic laboratories, which have the potential to improve the quality of life for current and future generations. Thanks to the willingness of most of the speakers in the session to contribute to this special issue, the following pages document the breadth of the topic as well as its importance to society. A couple of reviews allow us to make the point on two strategic issues for not only mineralogy, but also for the whole of society: the use of microporous geomaterials to produce and store energy and that of metastable geomaterials to protect the environment. Unfortunately, they could not be inserted in this special issue. Lumpkin et al. (2014) discuss the use of Th-U minerals in assessing the performance of high-level nuclear waste forms. They focus on information that can be obtained from natural analogues with regard to host-phase crystal chemistry, …

Producing a rational and straightforward scheme for the classification of complex mineral groups often implies a long and winding road. In the case of the amphibole supergroup, A0?1B2C5T8O22W2, efforts started in 1968, and proceeded under the guidance of Bernard Leake until 2006. In the last 20 years, however, discovery of new amphibole compositions (especially, CLi and WO2? amphiboles) clearly showed that a system based on stoichiometric ranges of A-, B- and T-group cations failed to represent such complexity. A major attention to crystal-chemistry, the use of the concepts of dominant valency, and classification based on A-, B- and C-group cations were discussed but not implemented during the almost 10-years discussion which produced the Leake et al. (1997) report. Unfortunately, the logic of minor changes and limited redefinitions eventually prevailed. However, these concepts germinated in the mineralogical literature and were implemented for smaller mineral groups (e.g., hellandite: Oberti et al. 2002; arrojadite: Chopin et al. 2006; epidote: Armbruster et al. 2006) until the dominance criterion was adopted by IMA-CNMCN (Hatert & Burke 2008). The newly approved scheme for the nomenclature and classification of the amphibole supergroup adheres to the concepts of dominant group valency and dominant ion. The hierarchy of classification proceeds through the W (-> groups), B (-> subgroups), and C and A (-> rootnames) ions in a rational and comprehensive scheme which takes into account amphibole stability based on synthesis work. The use of prefixes now refers to ANa C(Mg,Al) root compositions (starting points), with a few exceptions that recognize the petrological relevance of some C(Fe2+,Fe3+) rootnames. The new scheme implies redefinition of a number of rootnames and species, but the overall pattern is greatly simplified and can be easily handled by a series of inequalities. Hence, the present pain of expert mineralogists and petrologists will be hopefully compensated by the future relief for younger scientists. More important, the scheme will no longer allow oddities such as the use of different rootnames for compositions differing solely by homovalent cations (e.g., pargasite and ehimeite). In parallel with the preparation of the report on amphiboles, new nomenclature schemes for other mineral groups have been developed by other subcommitees (tourmaline: Henry et al. 2011; garnet: Grew et al. 2012), which are based on the dominant valency rule and the dominant ion criterion. This will hopefully bring consistency to these classification schemes. Major requirements for using these classification schemes effectively have been and should be a complete (multi-technique) chemical analysis and a correct crystal-chemical model for ion assignment. This is undoubtedly the route to be followed in the future for all mineral groups. Armbruster et al. (2006) E.J.M., 18, 551-567; Chopin et al. (2006) Am. Min., 91, 1260-1270; Grew et al. (2012) Am. Min. in press; Hatert & Burke (2008) Can. Min., 40, 679-710; Henry et al. (2011) Am. Min., 96, 895-913; Leake et al. (1997) Can. Min., 35, 219-246; Oberti et al. (2002) Am. Min., 87, 745-752.

Water is known to be an effective flux of mantle melting. Thus knowledge of its distribution and effects is critical for our understanding of geochemical fractionation within the Earth's mantle, since this is largely driven by melt production and migration. However, the influence of water on magmas can be difficult to distinguish from that produced by other factors, such as pressure and temperature. Our approach to this problem has been to compare the compositional and structural properties of clinopyroxene (an important mantle phase) crystallized from both water-rich and water-poor magmas. High pressure experiments were performed at 1.0-3.5 GPa and 1025-1190 C on a hydrous intraplate magma (nepheline basanite) at Macquarie University, Australia. Water contents ranging from 5.8 to 16.3 wt. % were dissolved in the coexisting melts. Clinopyroxenes crystallized from these experiments were analysed for major, minor and trace elements by electron microprobe and laser-microprobe ICP-MS at the GEMOC Analytical Facility, Macquarie University, Australia. Crystal chemical structural data, including lattice parameters and structure refinements, were obtained using single-crystal X-ray diffractometry at the CNR-Institute of Geoscience and Georesources, Pavia, Italy. Water concentrations in the melts were estimated from mass balances between run products and starting materials. Increasing pressure of formation was found to have a marked effect on both the compositions and structural properties of the clinopyroxenes crystallized from the hydrous melts. Augite crystals [Ca(Mg,Fe)Si2O6] become more jadeite-rich (NaAlSi2O6), but less calcic and Ti-rich as pressures of synthesis increase. These changes are accompanied by systematic decreases in cell volumes. Higher temperatures cause increases in both the clino-enstatite/clino-ferrosilite components [(Mg,Fe)2Si2O6] and the Ca-Tschermaks component (CaAlAlSiO6). Inclusion of these components also reduces cell volumes. Consistent with these changes, patterns of incompatible trace element incorporation also vary with concomitant reductions in the volumes of M1 and M2 sites. We evaluated the effects of H2O by applying the single-crystal clinopyroxene barometer of Nimis & Ulmer (Contrib. Mineral. Petrol., 133: 122-135, 1998) to our data. This barometer is distinctive in that it is based on the overall response of the crystal structure (principally cell volume) to pressure, rather than to specific compositional changes. It was also calibrated primarily for anhydrous melt compositions. When applied to our data, the Nimis & Ulmer (Contrib. Mineral. Petrol., 133: 122-135, 1998) barometer systematically underestimates pressures of synthesis, with the underestimation increasing at higher pressure. This is due to the comparatively large volumes of the crystals grown in our experiments. Thus at constant pressure, clinopyroxenes crystallized from H2O-rich melts have larger unit cell volumes (being comparatively enriched in diopside and hedenbergite) than those crystallized from equivalent anhydrous systems. This may partially be the result of the differential affects of H2O on the activity coefficients of pyroxene-forming melt components. But it also reflects the comparatively low temperatures of the hydrous experiments and the affect that this has on the activity coefficients of high and low volume components within the clinopyroxene crystal structure.

The structure of Ritipenem Acoxil, obtained by single crystal x-ray diffraction analysis, is reported and some stereochemical features are discussed. The compound exhibits a characteristic CD spectrum. The relevance of the C-5 configuration in the determination of the sign of the CD bands is also discussed.

Rearrangement of the tricarbonyl(cycloheptatriene)iron derivative 1 to 2 and 3 took place very readily in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) at room temperature. This finding is in striking contrast to the stability of 1 in MeOH under otherwise similar conditions. The isomerization processes which give rise to an equilibrium among 1, 2 and 3 must involve zwitterionic intermediates of the type 4, whose formation, consequently, is highly favored by HFIP. Heating 9 in HFIP brought about its rearrangement to 15. We suggest that formation of the zwitterionic intermediate 12 triggers a rearrangement of the carbocyclic moiety which can take place as a result of the high polarity and low nucleophilicity of HFIP. The rearrangement 9 → 15 could not be achieved by using other polar solvents such as methanol or nitromethane. This observation once again demonstrates how suitable HFIP is as a medium for isomerizations via zwitterionic intermediates. The role of traces of free acid, present even in purified HFIP, is discussed.

Fluoro-aluminoleakeite, ideally , is a new mineral of the amphibole group from Norra Kärr, Sweden (IMA-CNMMNC 2009-012). It occurs in a proterozoic alkaline intrusion that mainly comprises a fine-grained schistose agpaitic nepheline-syenite (grennaite). Fluoro- aluminoleakeite occurs as isolated prismatic crystals 0.10–2 mm long in a syenitic matrix. Crystals are light greenish-blue with a greenish-blue streak. It is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.14 g cm–3. In plane-polarized light, it is pleochroic, X = pale green, Y = dark green, Z = pale green; X ^ a = 62.9° (in β obtuse), Y || b. Fluoro-aluminoleakeite is biaxial negative, α = 1.632(1), β = 1.638(1), γ = 1.643(1); 2Vobs. = 98.0(4)°, 2Vcalc. = 95.5°.MFluoro-aluminoleakeite is monoclinic, space group C2/m, a = 9.7043(5) Å, b = 17.7341(8) Å, c = 5.2833(3) Å, β = 104.067(4)°, V = 882.0(2) Å3, Z = 2. The eight strongest X-ray diffraction lines in the powder-diffraction pattern are [d in Å, (I), (hkl)]: 2.687, (100), (31, 151); 4.435, (80), (021, 040); 3.377, (80), (131); 2.527, (60), (02); 8.342, (50), (110); 3.096, (40), (310); 2.259, (40), (71, 12) and 2.557, (30), (002, 061). Analysis, by a combination of electron microprobe and crystal-structure refinement, gives SiO2 58.61, Al2O3 7.06, TiO2 0.32, FeO 3.27, Fe2O3 6.05, MgO 8.61, MnO 0.73, ZnO 0.43, CaO 0.05, Na2O 9.90, K2O 2.43, Li2O 1.62, F 3.37, H2Ocalc. 0.50, sum 101.08 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F,Cl) p.f.u. with (OH) + F = 2 a.p.f.u., is A(Na0.65 O22W(F1.47OH0.53)Σ=2.00. Crystal-structure analysis shows CLi to be completely ordered at the M(3) site, and provided reliable site populations. Fluoro-aluminoleakeite is related to the end-member leakeite, , by the substitutions CFe3+ → CAl and WF → W(OH).

Rearrangement of the tricarbonyl(cycloheptatriene)iron derivative 1 to 2 and 3 took place very readily in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) at room temperature. This finding is in striking contrast to the stability of 1 in MeOH under otherwise similar conditions. The isomerization processes which give rise to an equilibrium among 1, 2 and 3 must involve zwitterionic intermediates of the type 4, whose formation, consequently, is highly favored by HFIP. Heating 9 in HFIP brought about its rearrangement to 15. We suggest that formation of the zwitterionic intermediate 12 triggers a rearrangement of the carbocyclic moiety which can take place as a result of the high polarity and low nucleophilicity of HFIP. The rearrangement 9 → 15 could not be achieved by using other polar solvents such as methanol or nitromethane. This observation once again demonstrates how suitable HFIP is as a medium for isomerizations via zwitterionic intermediates. The role of traces of free acid, present even in purified HFIP, is discussed.

Roberta Oberti (CNR-IGG Pavia, Italy) Structure refinement and structure modelling: a chemical probe for complex mineral groups Solid solution of many chemical species in a number of structural sites is a common feature of many mineral groups. In these cases, site preference and partitioning is a function of both the bulk composition and the intensive parameters of the system (P, T, fH2O...). In complex mineral groups, reliable models can be obtained only by comparative analysis of crystal-chemical databases built up with a multi-technique approach including structure refinement. On this basis, statistical analysis allows modelling of the crystal-chemical formula as a function of combination of subtle changes in the geometric and electronic descriptors obtained by structure refinement.

The synthetic LiGaSi2O6 clinopyroxene is monoclinic C2/c at room-T. Its experimental electron density, q(r), has been derived starting from accurate room-T single-crystal diffraction data. Topological analysis confirms an intermediate ionic-covalent character for Si-O bonding, as found by previous electron-density studies on other silicates such as diopside, coesite and stishovite. The non-bridging Si-O bonds have more covalent character than the bridging ones. The Ga-O bonds have different bonding characters, the Ga-O2 bond being more covalent than the two Ga-O1 bonds. Li-O bonds are classified as pure closed-shell ionic interactions. Similar to spodumene (LiAlSi2O6), Li has sixfold coordination, but the bond critical points associated to the two longest bonds are characterized by very low electron density values. Similar to what previously found in spodumene and diopside, OO interactions were detected from the topological analysis of q(r), and indicate a cooperative interaction among the lone pairs of neighbouring oxygen atoms. In particular, this kind of interaction has been obtained for the O1O1 edge shared between two Ga octahedra. Integration over the atomic basins gives net charges of -1.39(10), 2.82(10), 1.91(10) and 0.82(8) e for O (averaged), Si, Ga and Li atoms, respectively. Periodic Hartree-Fock and DFT calculations confirm the results obtained by multipole refinement of the experimental data. Moreover, the theoretical topological properties of the electron density distribution on the Si2O6 group are very similar to those calculated for spodumene.

Beside - or instead of - the classical accessory phosphates characterized by large-size cations, metamorphic rocks of sedimentary or hydrothermal derivation can bear phosphates of Mg, Fe and Mn which may contain in addition Al or larger-size cations. These are in particular wagnerite (Mg,Fe,Mn)2PO4(F,OH), lazulite (Mg,Fe)Al2(PO4)2(OH)2, and arrojadite-group minerals, presently defined as KNa4Ca (Fe,Mn,Mg)14Al(PO4)12(OH,F)2. The latter were long considered as restricted to granitic pegmatite but also occur in metaquartzite and in hydrothermal veins cross-cutting shale and iron-stone. Recent findings and our re-investigation of classical material reveal large compositional variations, which go so far beyond those suggested by the above formula that the mineral may act as a sink for Ba and Sr. These variations may, or may not, be related to pressures and temperatures of formation that cover a much broader range than anticipated. Together with new crystal-structure data, they imply complete reconsideration of the crystal-chemistry of the arrojadite group, which will be briefly outlined (but thoroughly addressed in the companion contribution by Oberti et al. [1]), including an assessment of the role of lithium, fluorine and OH groups in this complex structure. Wagnerite and lazulite have received more attention from a petrological and experimental point of view, so that thermodynamic data are now available for lazulite and the Mg-OH end-member of wagnerite [2, 3, 4]. Application of these data to natural assemblages reveals the dramatic effect of fluorine in stabilizing wagnerite toward low pressures and accounts for the scarcity (absence?) of lazulite in HP and UHP rocks. In addition to these phase relations and compositional variables that are of direct petrological relevance, wagnerite-group minerals also show an uncommon structural variable. Periodic faulting of the arrangement of the fluorine atoms creates a modulation of the structure along b , which results in a variety of polytypes (and space groups) with at least 2b, 5b, 7b and 9b superstructures [5, 6, 7]. The relative importance of P and T, chemistry and kinetics in the control of this structural parameter will be discussed. Therefore, even if restricted to Ca-poor rocks, these often neglected accessory phosphates should rather be considered, through their structure and composition, as a valuable source of information supplementing the classical geochemical and petrological approach. [1] Oberti R., Cámara F., Chopin C. (2005) This meeting. Geophys. Res. Abstracts. [2] Schmid-Beurmann P., Brunet F., Kahlenberg V. (2003) Berichte der DMG, Bh. 1, 175. [3] Brunet F., Morineau D., Schmid-Beurmann P. (2004) Mineral. Mag. 68, 123- 124. [4] Leyx C., Chopin C., Van Miltenburg C.J., Brunet F., Parra T. (2004) EMPG X abstr., Lithos 73, S68. [5] Ren L., Grew E.S., Xiong M., Ma Z. (2003) Canad. Mineral., 41, 393-411. [6] Chopin C., Armbruster Th., Leyx C. (2003) Geophys. Res. Abstracts, 5, 08323. [7] Chopin C., Armbruster Th., Baronnet A., Grew E.S. (2004) Abstr. 62-7, 32th IGC, Florence.

This work reports the synthesis of ferri-clinoholmquistite, nominally square(Li2)(Mg3Fe23+)Si8O22(OH)(2), at varying f(O2) conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mossbauer and Raman) techniques. Under reducing conditions (less than or equal to NNO+1, where NNO = Nickel-Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions (less than or equal to NNO+1.5), the amphibole yield is much lower (

Non-metamict betafite, a pyrochlore-group mineral with general formulaA2−mB2XO6Y(O,OH,F)1−n·pH2O and 2 Ti > Nb+Ta and U > 20% at theAsite, has been found at Le Carcarelle, (Latium, Italy). It occurs within miarolitic cavities of a foid-bearing syenitic ejectum enclosed within the pyroclastic formation known as “ignimbrite C”, which belongs to the main effusive phase of the Vico volcanic complex. The host rock is composed of K-feldspar, biotite, augitic clinopyroxene, magnetite and minor sodalite. Electron microprobe analyses gave the following crystal-chemical formula: (Ca1.24Na0.17U0.49REE0.03)Σ=1.93(Ti1.05Nb0.76Zr0.14Fe0.04Ta0.01)Σ=2.00O6(O,OH). Compared with other occurrences reported in the mineralogical literature, betafite from Le Carcarelle is extremely enriched in U and depleted in Th. Due to its young age of formation (∼150 k.y.), this betafite sample is highly crystalline, thus allowing structure refinement of unheated material. Betafite from Le Carcarelle is cubicFdm, witha= 10.2637(13) Å, andV= 1081.21(35) Å3, and has a smallerAsite (consistent with the higher U content), and a larger and more distortedBsite (consistent with the higher Ti content) than calciobetafite from Campi Flegrei, Italy (Mazzi and Munno, 1983). Analysis of the atomic displacement parameters provides evidence for static disorder at theXsite.

Ferrian magnesian spodumene was synthesized in the MLFSH system at P=0.4 GPa, T=700 °C, fO2=NNO+2.3. The space group at room T is P21/c [a=9.638(3) A, b=8.709(2) A, c=5.258(2) A, β=109.83(3)∘, V=415.2 A3]. The structure is topologically equivalent to that of ferrian spodumene, LiFeSi2O6, and has two symmetrically independent tetrahedral chains, A and B, and two independent octahedral sites, M1 and M2. The crystal-chemical composition was determined combining EMP, SIMS and single-crystal XRD analysis, yielding M2(Li0.85Mg0.09Fe2+ 0.06) M1(Fe3+ 0.85Mg0.15)Si2O6. Li is ordered at the M2 site and Fe3+ is ordered at the M1 site, whereas Mg (and Fe2+) distribute over both octahedral sites. Structure refinements done at different temperatures (25, 70, 95, 125, 150 and 200 °C) allowed characterization of a reversible displacive P21/c→C2/c transition at 106 °C. Previous HT-XRD studies of Li-clinopyroxenes had shown that the transition temperature is inversely related to the size of the M1 cation. For the crystal of this work, the aggregate ionic radius at M1 is longer than that of ferrian spodumene, for which the transition temperature is −44 °C. The higher transition temperature observed can only be explained on the basis of the shorter aggregate radius at the M2 site (due to the presence of Mg substituting after Li), in keeping with the results obtained for ferromagnesian P21/c pyroxenes. The effects of all the chemical substitutions must be considered when modelling transition temperatures and thermodynamic behaviour in clinopyroxenes.

The P21/m↔C2/m displacive phase transition in the synthetic end-member amphibole Na NaMg Mg5 Si8 O22 (OH)2 has been studied by monitoring changes in unit-cell parameters and the intensities of superlattice reflections at 25–400 °C. This amphibole allows investigation of the effects of compositional variations at the A- and B-group sites upon the transition. Polynomial fitting of a 24 Landau potential to the evolution of the order parameter with T yielded a T c of 257 ± 3 °C, and Landau coefficients compatible with a second-order transition. Structure refinement of single-crystal data collected at 25, 140, 270 and 370 °C allowed modelling of the structural changes as a function of T and symmetry. Crystal-chemical analysis suggests that differences in T c in cummingtonites and in the crystal of this work depend mainly upon the relations between the aggregate ionic radii of the B- and C-group cations.

Natural melanite garnets from carbonatitic rocks have beenstud ied by a multitechnique approach based onboth experimental (chemical, diffractometric and spectroscopic) methods and full-multiple scattering calculations of the X-ray absorption near-edge structure. Inparti cular, the site location and geometry of trace amounts of neodimium (from 176 to 1074 ppm) and cerium (791 ppm) in natural garnets have been studied by fluorescence-detected X-ray absorption fine-structure spectroscopy (XAFS) at high energy. The measurements, done at both Nd K (43569 eV) and Ce K (40443 eV) edges, demonstrate that, in all the samples, the trace elements are located in the dodecahedral X site and not in ill-defined defects. The local geometry around the two rare-earth elements is compatible with their ionic radius and is compared with that of Ca, the major element at the X site, as determined by single-crystal X-ray diffractiondata. This work represents the first example of direct investigation of trace-level REE coordination in natural garnets, and confirms the great relevance for the Earth Sciences of the use of fluorescence XAFS at high energy.

Titanite/liquid partition coefficients for most of the trace elements relevant in petrogenetic studies are provided for titanite-saturated liquids equilibrated at 1.5 GPa and 850 °C starting from lamproitic compositions. The high compatibility observed for REE, HFSE, Sr, V and Sc, and the strong incompatibility observed for actinides, large ion lithophile and light elements are discussed in terms of available crystal-chemical mechanisms for incorporation and crystal-structure control. The exchange vectors Na1Ca−1 and Al1Ti−1 allow local charge balance to be achieved after incorporation of REE3+ and R5+ at the Ca and Ti site, respectively. The significant amounts of H measured are also relevant in this regard [the exchange mechanism being (OH)1O−1 at the O1 site]. The incorporation of U4+ and Th4+ at the Ca site is scarce, and is likely balanced by that of Mg2+ at the Ti site; both these substitutions are responsible for strong structural strain. Titanite can thus be considered an important repository for REE and HFSE in metamorphic and igneous rocks, and its role must be accounted for when modelling trace-element residence during metamorphic reactions and late magmatic crystallisation history. Due to the measured differences in compatibility, titanite crystallisation increases the values of Nb/Ta and LREE/HREE ratios in residual liquids. The similar compatibility of U and Pb makes titanite suitable for U–Pb geochronology of igneous rocks only after common Pb correction. Finally, this study confirms that the titanite end member is not suitable for radioactive waste disposal due to the discussed crystal-chemical constraints, and that titanite-based waste forms should contain high amounts of Na+ and Mg2+.

In the title compound the pyrazole and benzene rings form a dihedral angle of 64.5 (1) o . Neither ring deviates significantly from planarity. There is an intramolecular hydrogen bond between atom N12 and atom O23 [N12...O23 2.682 (4) A, N12-H12...O23 102.9 (2) o ]; all other bond distances and angles are within the expected ranges

New partition coefficients between liquid and pargasitic/kaersutitic amphiboles (Amph=LDNb,Ta) experimentally determined for Nb and Ta at upper-mantle conditions, combined with single-crystal structure refinement of the synthesised amphiboles, show that Amph=LDNb;Ta are strongly dependent on the structure and composition of both amphibole and melt. The correlation of the Amph=LDNb;Ta with the amphibole oxy-component is explained by the ordering of Nb and Ta at the M1 site, contributing with the fraction of Ti at M1 to locally balance the O3O23HO3(OH)3 substitution. In our set of dehydrogenated amphiboles, variations in the SiO2 content of the melt from 41.5 to 54.6 correspond to a six-fold increase of the Amph=LDNb;Ta, in which Amph=LDNb varies from 0.14 to 0.71 and Amph=LDTa from 0.11 to 0.54. Partition coefficients for Nb and Ta abruptly increase in Ti-depleted compositions (Amph=LDNb up to 1.63 and Amph=LDTa to 1.00). The ratio of DNb to DTa (Amph=LDNb=Ta) varies from 0.71 to 1.63, and is a function of the M1 site dimension, which in turn depends on its Fe, Mg and Ti contents. The observed variations can be explained by assuming that the ionic radius of Nb is (V0.01^0.02 Aî ) larger than that of Ta, contrary to the common assumption that they are both equal to 0.64 Aî . We calibrated a simplified model for the prediction of Amph=LDNb=Ta values shown to be negatively related mainly to mg# [Mg/(Mg+Fe)] and to Ti content. High-mg# amphiboles have Amph=LDNb=Ta close to unity, so the low Nb/Ta found in convergent margin volcanics and in the continental crust cannot be explained by the involvement of amphibole in the mantle wedge. Amphibole in the subducting slab may have lower mg# and consequently high Nb/Ta values, and thus may give rise to subchondritic Nb/Ta values in coexisting melts. Nb/La is also negatively correlated with mg#, and strongly increases in Ti-depleted compositions.

OBJECTIVE: To assess how clinical and angiographic findings are related to the decision to carry out coronary angioplasty (PTCA) or coronary bypass grafting in patients with multivessel coronary artery disease. DESIGN: Prospective survey carried out in 14 centres in the Lombardia region of Italy. PATIENTS: 1468 consecutive patients under going coronary arteriography for known or suspected ischaemic heart disease between May and October 1994, who were found to have multivessel coronary artery disease. MAIN OUTCOME MEASURES: Multivariate analysis was undertaken using stepwise logistic regression to identify the clinical and angiographic variables correlated with revascularisation (v medical treatment) in all of patients, and with surgery (v angioplasty) in the subset of revascularised patients. RESULTS: In all patients the clinical decision after coronary arteriography was made by physicians of each participating centre on the basis of their experience and clinical judgment: 53% of patients had bypass surgery, 28% had PTCA, and 19% continued medical treatment. The choice of a revascularisation procedure was directly related to a clinical diagnosis of unstable angina (P < < 0.001), the presence of left anterior descending artery disease (P < < 0.001), and to an ejection fraction > or = 40% (P < < 0.001), and inversely related to history of previous coronary bypass surgery (P < < 0.001). In revascularised patients, bypass surgery was the preferred treatment in patients with left anterior descending artery disease (P < < 0.001), three-vessel disease (P < < 0.001), and in those with at least one occluded vessel (P = 0.008). The choice of PTCA was significantly related to history of previous PTCA (P < < 0.001) or coronary bypass surgery (P < < 0.001), to a clinical diagnosis of non-Q wave myocardial infarction (P = 0.002), and to the possibility of implanting an intracoronary stent (P = 0.01). CONCLUSIONS: Bypass surgery is still the most widely used treatment for patients with multivessel coronary artery disease. This analysis provides a basis for comparison with future developments in the treatment of such patients. Further advancements in PTCA technology are needed to tilt the balance in favour of this less invasive procedure.

A Moraxella bovis strain was isolated from a kerato-conjunctivities lesion of a calf in Villa Valeria (Córdoba); it was used to establish improved cultural conditions, such as nature and concentration of carbon and nitrogen sources, and pH control in shaken flasks. The selected conditions were assayed for biomass production in a bench-top fermentor. The strain is used by the pharmaceutical industry to produce vaccines and adjuvants. In the initial condition (48 h culture on blood agar) 0.019 g biomass/l.h-1 was obtained. With the use of liquid defined medium with pH control, productivity was increased to 0.153g/l.h-1, with optimum harvest time of 32 h.

Recent work on spinel-facies mantle assemblages has shown that Amph/CpXDTi (a) are always higher than 1; (b) may vary in the range 2.7-8.9, and (c) are significantly higher than those of REEs and Zr (Vannucci et al. , 1995). Therefore, in amphibolebearing systems Ti can strongly fractionate relative to REEs and Zr, with important implications for the modelling of geochemical processes. The behaviour of Ti 4§ in amphibole is rather complex, and has recently been the subject of a number of systematic studies based on complete (EMP+SIMS) chemical characterization and X-ray single-crystal structure-refinement (SREF) of calcic, sodic-calcic and sodic amphiboles (Oberti e t al., 1992, Hawthorne et al. , 1993,1998). These studies have shown that Ti 4§ can enter the amphibole structure according to three different crystalchemical mechanisms: (a) T2Ti4+ T2Si4+ 1; (b) M1Ti4+ O302MI(Mg,Fe)2_~ ~ (c) M2'M3Ti4+

The electron density distribution of diopside at ambient conditions has been determined by X-ray diffraction and refined through the multipole model of electron density, following the formalism of Stewart [1]. The final multipole refinement includes two extinction parameters, according to the Sabine model, and two kappa expansion/contraction parameters (one for O and the other for Si, Ca and Mg valence monopoles). The expansions over the spherical harmonics were truncated at the octopole level. Topological analyses of the electron density and its Laplacian distributions [2] reveal that the bonding character of the four Si-O bonds is intermediate between ionic and covalent, as previously found for stishovite and coesite. As expected, the Mg-O and Ca-O bonds are definitely ionic. Determination of the atomic basins results in charges of +3.2(2) e for Si and -1.6(1) e, on average, for the oxygen atoms. The charges calculated for Mg and Ca are very close to the formal values. Our atomic charges are then more ionic than the corresponding ones determined by Sasaki et al. [3]. The program VALTOPO [4] was used for refinements and topological analysis of the experimental density. [1] Stewart R. F., Acta Crystallogr. Sect. A, 1976, 32, 565. [2] Bader R. F. W., Atoms in Molecules - A Quantum Theory, Oxford University Press, Oxford, 1994. [3] Sasaki S., Fujino K., Takéuchi Y., Sadanaga R., Acta Cryst. Sect. A, 1980, 36, 904. [4] Bianchi R., Forni A., J. Appl. Crystallogr., 2005, 38, 232.

Tetracyanoethene reacted with tetracyclo [5.3.2.02,10.03.6] dodeca-4,8,11-triene (1) according to two competitive reaction modes, both involving the sole homotropilidene moiety, to give a mixture of adducts 4 and 6. Structure 6 was established by X-ray analysis. Compounds 4 and 6 result from a thermally allowed homocycloaddition and a forbidden[Π25 + σ25+ Π2s+Π2s] reaction, respectively. The reaction rate and the 6:4 ratio increased on passing from benzene to nitromethane as reaction medium. The homo-Dies-Alder reaction leading to 4 was shown to be reversible. In methanol compound 4 gave rise to a zwitterion which was trapped by solvent. Reaction mechanisms are discussed. A zwitterion is proposed as intermediate on the pathway to 6 whereas experimental findings do not permit a definitive choice between an ionic two step and a concerted cycloaddition in the formation of 4. The neutral and base catalyzed addition of methanol to the tetracyanoethylene moiety of 4, 6 and related derivatives was also investigated.

Coarse grained garnet-pyroxene coronas in anorthositic gabbros of the Bergen and Sognefjord areas preserve relics of two stages of reaction during cooling from magmatic T: (1) ol + plag→cpx I+ opxI + spn; (2) cpxI + opxI + spn + plag→cpxII + opxII + gnt.

The photochemical reaction of 1,4-dicyanonaphtalene (1) in the presence of methylbenzenes (2a–c) in acetonitrile affords 1 - benzyl - 4 - cyanonaphtalenes (3), 1 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (4), 2 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (5 and 6) and the tetracyclic derivatives 7 and 8. Compounds 3, 7 and 8 are not the products of subsequent transformations of compound 4. No photochemical reaction is observed in non-polar media, in which, on the contrary, exciplex emission is detected. Experiments in the presence of electron acceptors, electron donors and strong acids support the idea that the reaction is initiated by electron transfer from the methylbenzenes to singlet excited 1, followed by protolytic equilibrium of the benzylic radical cation to the corresponding radical, which is the attacking species.

3,4-Dihydroisoquinoline-N-oxide 1 reacted readily with both acyclic (Z)- and (E)-disubstituted alkenes bearing electron-attracting substituents (methoxycarbonyl, cyano, phenylsulphonyl and benzoyl groups) and with cyclic derivatives (e.g. maleimides) to give mixtures of the two possible diastereoisomers. Similar amounts of endo - and exo -adducts were formed in the reactions of (Z)-cyano, methoxycarbonyl and benzoyl derivatives whereas exo -addition clearly won over its endo -counterpart in the case of (Z)-(phenylsulphonyl) and cyclic derivatives. High exo -selectivity was also observed in the sluggish reactions of 1 with electron-rich alkenes [(Z)-stilbene, vinylene carbonate, acenaphthylene etc.] Our results, which revise previous literature data, clearly show that an “ endo -rule” does not hold for the reactions of 1 with (Z)-1,2-disubstituted alkenes. We conclude that in these reactions repulsive steric interactions either counteract efficientlt or clearly win over stabilizing secondary orbital overlaps in controlling endo/exo -selectivity. These reactions were found reversible under mild conditions so that relative formation rates of related pairs of (Z)- and (E)-dipolarophiles in cycloreversion processes of isoxazolidines could be determined; as a rule (E)-alkenes are extruded faster then (Z)-isomers. These results provide unambiguous experimehntal evidence that increase in steric compression between the substituents in (Z)-alkenes on there way toward transition state, is not a major factor in dertermining their lower reactivity with respect to (E)-isomers in 1,3-dipolar cycloadditions.