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In this paper, we presented a detailed study on the effect of electron beam diameter, spectral overlapping, and element assay sequence on quantitative uncertainties of electron probe microanalysis. With a fixed electron beam diameter of 1 [mu]m for external standard materials, the sample signal intensities were found to decline with the increasing electron beam diameter from 1 to 300 [mu]m, resulting in a sample concentration bias higher than 2% and even up to 20%. Only when electron beam diameter difference between external standard materials and analyzed samples was less than 20 [mu]m, the concentration bias was negligible. The spectral overlapping interference investigation revealed that in the case of shoulder-peak overlapping it was possible to remove the concentration bias by appropriately choosing L value and background signal picking-up position. However, quantification calibration was mandatory when there existed on-peak spectral overlapping interference. For sphalerite samples, this effect was prominent, and the artificially produced Na.sub.2O concentration can be 6.23% (±0.30%, 2[sigma], n = 12) due to on-peak spectral interference of Zn on Na. Furthermore, because of the on-peak spectral interference of S on Mo, the quantification accuracy of Mo was found to be dependent on the mass fraction of S in the studied samples. We also observed that element assay sequence highly affected the quantification accuracy of geological samples containing alkali. In element composition analysis of albite samples, when using matrix-matched calibration standard, the average Na.sub.2O concentration decreased substantially from 11.55 to 5.61% when Na was measured the first and last, respectively., Author(s): Minwu Liu [sup.1] , Xijuan Tan [sup.1] Author Affiliations: (1) grid.440661.1, 0000 0000 9225 5078, Laboratory of Mineralization and Dynamics, College of Earth Sciences and Land Resources, Chang'an University, [...]

Byline: N. V. Chalapathi Rao (1), Rajesh K. Srivastava (1) Keywords: Petrology; Geochemistry; Kimberlite; Diamond; India Abstract: The petrology and geochemistry of some new occurrences of Mesoproterozoic diamondiferous hypabyssal-facies kimberlites from the Chigicherla, Wajrakarur-Lattavaram and Kalyandurg clusters of the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton (EDC), southern India, are reported. The kimberlites contain two generations of olivine, and multiple groundmass phases including phlogopite, spinel, calcite, dolomite, apatite, perovskite, apatite and rare titanite, and xenocrysts of eclogitic garnet and picro-ilmenite. Since many of the silicate minerals in these kimberlites have been subjected to carbonisation and alteration, the compositions of the groundmass oxide minerals play a crucial role in their characterisation and in understanding melt compositions. While there is no evidence for significant crustal contamination in these kimberlites, some limited effects of ilmenite entrainment are evident in samples from the Kalyandurg cluster. Geochemical studies reveal that the WKF kimberlites are less differentiated and more primitive than those from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton. Highly fractionated (La/Yb = 108--145) chondrite-normalised distribution patterns with La abundances of 500--1,000 x chondrite and low heavy rare earth elements (HREE) abundances of 5--10 x chondrite are characteristic of these rocks. Metasomatism by percolating melts from the convecting mantle, rather than by subduction-related processes, is inferred to have occurred in their source regions based on incompatible element signatures. While the majority of the Eastern Dharwar craton kimberlites are similar to the Group I kimberlites of southern Africa in terms of petrology, geochemistry and Sr--Nd isotope systematics, others show the geochemical traits of Group II kimberlites or an overlap between Group I and II kimberlites. Rare earth element (REE)-based semi-quantitative forward modelling of batch melting of southern African Group I and II kimberlite source compositions involving a metasomatised garnet lherzolite and very low degrees of partial melting demonstrate that (1) WKF and NKF kimberlites display a relatively far greater range in the degree of melting than those from the on-craton occurrences from southern Africa and are similar to that of world-wide melilitites, (2) different degrees of partial melting of a common source cannot account for the genesis of all the EDC kimberlites, (3) multiple and highly heterogeneous kimberlite sources involve in the sub-continental lithospheric mantle (SCLM) in the Eastern Dharwar craton and (4) WKF and NKF kimberlites generation is a resultant of complex interplay between the heterogeneous sources and their different degrees of partial melting. These observations are consistent with the recent results obtained from inversion modelling of REE concentrations from EDC kimberlites in that both the forward as wells as inverse melting models necessitate a dominantly lithospheric, and not asthenospheric, mantle source regions. The invading metasomatic (enriching) melts percolating from the convecting (asthenosphere) mantle impart an OIB-like isotopic signature to the final melt products. Author Affiliation: (1) Igneous Petrology Laboratory, Department of Geology, Banaras Hindu University, Varanasi, 221005, India Article History: Registration Date: 25/07/2008 Received Date: 17/04/2008 Accepted Date: 24/07/2008 Online Date: 07/08/2008 Article note: Communicated by T.L. Grove.

Poppiite, a new mineral from Gambatesa mine (Val Graveglia, Genova, Northern Italy), is the [V.sup.3+] end-member of the pumpellyite group [[sup.[VII]][([Ca.sub.7.68][Na.sub.0.27][K.sub.0.03] [Rb.sub.0.02]).sub.[summation of]8.00] [sup.[VI]][([V.sup.3+.sub.1.26][Fe.sup.3+.sub.1.02] [Mg.sub.0.78][Mn.sup.2+.sub.0.59][Al.sub.0.31] [Cu.sup.2+.sub.0.04]).sub.[summation of].4.00] [sup.[VI]][([V.sup.3+.sub.6.89][Al.sub.1.07][Ti.sub.0.04]).sub.[summation of]8.00] [sup.[IV]][([Si.sub.11.69][Al.sub.0.31]).sub.[summation of]12.00] [O.sub.42][(OH).sub.14]; C2/m, a = 19.2889(6), b = 6.0444(2), c = 8.8783(3) [Angstrom], [beta] = 97.328(2)[degrees], V = 1026.66(6) [[Angstrom].sup.3], [D.sub.meas] = 3.36(2) g/[cm.sup.3], and [D.sub.calc] = 3.44 g/[cm.sup.3]]. Poppiite crystals, with size varying from 0.1 to 0.6 mm, are minute, greenish-brown, and prismatic, and are associated with roscoelite, ganophyllite, manganaxinite, goldmanite, and calcite. The strongest lines in the X-ray powder diffraction pattern [[d.sub.obs] ([Angstrom]), [I.sub.rel], (hkl)] are: 2.930, 100, (511); 3.817, 70, (202); 2.548, 65, ([bar.3]13); 2.551, 62, (420); 1.612, 57, ([bar.7]31,424); and 2.367, 51, (222, 403). Poppiite is optically negative, with [2V.sub.calc] = 44[degrees], [n.sub.[alpha]] = 1.768(9), [n.sub.[beta]] 1.804(8), [n.sub.[gamma]] 1.810(9). The pleochroic scheme is [alpha] = light yellowish brown, [beta] = deep greenish brown, and [gamma] = brown to reddish brown. The crystal structure was refined using 1918 unique reflections to R = 0.0307. Like the other pumpellyite-group minerals the crystal structure of poppiite consists of chains of edge-sharing octahedra linked by Si[O.sub.4], [Si.sub.2][O.sub.7], and Ca[O.sub.7] polyhedra. Keywords: New mineral, analysis chemical (mineral), crystal structure, optical properties, XRD data

First-principles calculations within the local density and pseudopotentiai approximations were performed to investigate the effects of pressure on the energetics and structural behavior of charged vacancy defects in MgO. The simulations were performed for a supercell containing 216 atoms with their positions being fully optimized. In particular, the formation and migration energies of cation and anion vacancies were shown to substantially increase over the pressure regime of the Earth's mantle. Our results thus suggest that pressure should suppress intrinsic diffusion mediated by ionic vacancies in MgO over the mantle pressure regime. The calculated three-dimensional data sets for atomic displacements and electron charge density were explored in detail using an interactive visualization system. Although the atomic and electronic structures are highly distorted in the close vicinity of the defects (i.e., in the region covering up to the nearest and next-nearest atoms), the effects are not negligible at farther distances. Keywords: Defects, mantle minerals, high pressure, rheology, first-principles calculations, scientific visualization

The effect of pressure upon hydrogen bonding in synthetic end-member clinochlore, ([Mg.sub.5]Al)([Si.sub.3]Al)[O.sub.10][(OH).sub.8], has been studied in situ by high-pressure micro-Raman spectroscopy in a moissanite-anvil cell to 26.5 GPa at 300 K. The ambient spectrum consists of three OH-stretching bands between 3400 and 3650 [cm.sup.-1], attributed to the hydrogen-bonded interlayer OH, and a narrow band at 3679 [cm.sup.-1] that is assigned to the non-hydrogen-bonded OH groups of the talc-like 2:1 layer. The pressure dependence of the OH modes is linear up to 6 GPa. Near 9 GPa a major discontinuity occurs in the pressure dependence of the interlayer OH-stretching modes. It involves frequency increases >100 [cm.sup.-1] that indicate major changes in hydrogen bonding. The OH mode of the 2:1 layer does not show discontinuous behavior at 9 GPa. A further discontinuity occurs at ~16 GPa. This discontinuity affects both interlayer and 2:1 OH, and is likely to be associated with a change in the overall compression mechanism of clinochlore. The spectroscopic behavior is a completely reversible function of pressure. Predictions based upon recent high-pressure diffraction studies of hydrogen bonding and compression of clinochlore suggest that the 9 GPa transition is associated with attainment of an [O.sup.2-]-[O.sup.2] -contact distance of 2.7 [Angstrom].

High resolution neutron powder diffraction has been used to determine lattice parameter variations of deuterated lawsonite across the Cmcm [left and right arrow] Pmcn and Pmcn [left and right arrow] [P2.sub.1]cn phase transitions, in the temperature interval 1.6-505 K. The variations are reversible through heating and cooling cycles. Strain analysis, based on a displacive model of the transitions with saturation temperatures to describe the temperature-independent behavior as T [right arrow] 0 K, shows that the data are consistent with a tricritical transition at 271 [+ or -] 2 K and a second-order transition at 155 [+ or -] 1 K. Comparisons with strains from published dilatation data for a natural (hydrogenated) sample highlight aspects of the transitions that are most dependent on the behavior of protons in the structure. Replacing H by D causes the low temperature transition point to be increased by ~27 K and an anomaly in the strain evolution of the Pmcn transition to increase from ~225 to ~250 K. The transition point of the high-temperature transition remains the same within [+ or -] ~2 K. We conclude that proton ordering and displacive contributions are both important in the 271 K transition, though with the displacive component providing the initial symmetry-breaking mechanism. Structural changes that are more dependent on the behavior of H or D become important ~20-50 K below this. Strains for the Pmcn [left and right arrow] [P2.sub.1]cn transition are consistent with a transition driven by a single order parameter. The data are used to determine values for strain/order parameter coupling coefficients for calculation of elastic anomalies due to the phase transitions.

The distribution of bonds associated with the M2 sites in various well-ordered pyroxene minerals is determined using a topological analysis of electron density in the manner proposed by Bader (1998). Each M2 atom is bonded to 2 O1 and to 2 02 atoms, and to zero, one, two, or four bridging 03 atoms. Each of the symmetries displayed by pyroxenes have their own bonding systematics, and each pyroxene-to-pyroxene phase transition involves a change in bonding to M2. As a function of temperature or pressure, the bonding changes appear as a well-defined sequence of steps that can be related to the degree of distortion from the ideal closest packing of anions. It is proposed that the condition at which an individual phase transition occurs is related to M2-Si repulsion through a shared edge. The bonding analysis should provide a qualitative means to interpret the behavior of all pyroxene structures over T, P, and x, and may guide the interpretation of the changes in properties observed by techniques other than X-ray diffraction, such as Raman spectroscopy.

A Sr-exchanged heulandite crystal of composition [Sr.sub.4.35][Ca.sub.0.13]([Al.sub.8.96][Si.sub.27.04][O.sub.72]).26[H.sub.2]O was used for stepwise dehydration experiments. The crystal was heated for approximately 12 h from room temperature to 250[degrees]C in steps of 50[degrees]C using an airflow-heater device. For single-crystal X-ray data collection the crystal was quenched to -173[degrees]C with liquid-[N.sub.2] on the diffractometer. Due to pronounced Sr order deviating from the topological symmetry C2/m, the structure was refined in space group Cm for each dehydration state. The initial [H.sub.2]O content of 26 molecules per formula unit (pfu) at room temperature decreased to 17 molecules pfu after heating at 250[degrees]C. Heating to 270[degrees]C mechanically destroyed the crystal and a completely dehydrated state could not be studied. The loss of [H.sub.2]O and accompanying migration of Sr caused a change of cell parameters: a and c slightly decreased, b decreased, and [beta] remained invariant, leading to a reduction of the cell volume. As Sr loses [H.sub.2]O upon dehydration, it moves toward the C rings and forms stronger bonds to the tetrahedral framework. With increasing dehydration the A and B ring become slightly compressed and elongated. Initially highly populated Sr sites split into less populated sites caused by the loss of surrounding [H.sub.2]O molecules.

This paper describes local mass transfer and fluid-rock interaction in epidote-blueschist subfacies basic schist around retrograde dolomite + calcite veins in the Nishisonogi Metamorphic Rocks, southwest Japan. The veins have alteration zones on both sides. The mineralogical and chemical changes during alteration were documented along two sample traverses normal to the veins. Approaching the veins, the peak metamorphic assemblage (winchite + epidote + chlorite + calcite + albite + quartz) has been modified by progressive breakdown of amphibole, epidote, and calcite to illite and dolomite. Mass-balance calculations using the isocon method reveal that [CO.sub.2] and K were added to the basic schists, and Ca was removed during alteration. The mass balance does not hold for these components between the vein + alteration zone and protolith as a whole. These findings suggest that the vein formation and metasomatism represent a process driven by fluid flow and long-distance element transport. Possible reaction paths between the vein-fluids and basic schists were estimated from the progressive change of mineral assemblages in the alteration zones. The phase relations on ionic activity diagrams indicate an increase in [logf.sub.[CO.sub.2]] and decreases in log([a.sub.[Ca.sup.2+]]/[[sigma].sub.[Ca.sup.2]]+[a.sup.2.sub.H+]) and log([a.sub.[Mg.sup.2+]]/[[sigma].sub.[Mg.sup.2+]][a.sup.2.sub.H+]) with progress of the alteration. Although a change in log([a.sub.K+]/[[sigma].sub.K+][a.sup.2.sub.H+]) is poorly constrained on the activity diagrams, the mass balance suggests a concentration gradient of K across the alteration zones. Hence, the reaction paths and mass balance calculations suggest that a combination of the concentration gradients of C[O.sub.2], Ca, Mg, and K produced by the vein-fluids drove the alteration process.

This work provides a crystal-chemical description of the trioctahedral sheet in 1M mica polytypes of C2/m symmetry. Some octahedral parameters were found to be related strictly to octahedral chemical composition, whereas others were related to the overall layer chemistry. As a general rule, the M1 site is more affected by octahedral chemical composition than the M2 site, and octahedral distortions are more affected than octahedral size. This behavior is attributed to the constraints related to edge-sharing octahedra and octahedral-tetrahedral coupling, which involves the sharing of the apical tetrahedral oxygen atom between the tetrahedron and octahedron. A more quantitative explanation was sought by considering expressions that relate octahedral parameters as a function of atomic coordinates and unit-cell parameters. This procedure identified those parameters affected by local distortions and those that are a function of a more global effect and whose variation greatly affects the layer. Local distortions are obviously more likely a result of local chemical composition. The size and distortion of the octahedral sheet seem to be independent for the database of samples considered. The [alpha] angle was found to be a complex parameter required to: (1) fit tetrahedral and octahedral lateral dimensions; (2) fit tetrahedral topology to its local chemical composition, and (3) fit the interlayer cation electrostatic interactions.

Sulfate-rich acid waters produced by oxidation of sulfide minerals enhance U mobility around U ores and U-bearing radioactive waste. Upon evaporation, several secondary uranyl minerals, including many uranyl sulfates, precipitate from these waters. The zippeite-group of minerals is one of the most common and diverse in such settings. To decipher the nature and crystal chemistry of the zippeite-group, the crystal structure of a new natural hydrated Mg uranyl sulfate related to Mg-zippeite was determined. The mineral is named marecottite after the type locality, the La Creusaz U prospect near Les Marecottes, Western Swiss Alps. Marecottite is triclinic, P[bar]1, with a = 10.815(4), b = 11.249(4), c = 13.851(6) [Angstrom], [alpha] = 66.224(7), [beta] = 72.412(7), and [gamma] = 69.95(2)[degrees]. The ideal structural formula is [Mg.sub.3][([H.sub.2]O) .sub.18][[(U[O.sub.2]).sub.4][O.sub.3](OH)[[(S[O.sub.4]).sub.2]].sub.2] [([H.sub.2]O).sub.10]. The crystal structure of marecottite contains uranyl sulfate sheets composed of chains of edge-sharing uranyl pentagonal bipyramids that are linked by vertex-sharing with sulfate tetrahedra. The uranyl sulfate sheets are topologically identical to those in zippeite, K[(U[O.sub.2]).sub.2](S[O.sub.4])[O.sub.2]*2[H.sub.2]O. The zippeite-type sheets altemate with layers containing isolated Mg[([H.sub.2]O).sub.6] octahedra and uncoordinated [H.sub.2]O groups. The uranyl sulfate and Mg layers are linked by hydrogen bonding only. Magnesium-zippeite is redefined as Mg[([H.sub.2]O).sub.3.5][(U[O.sub.2]).sub.2](S[O.sub.4])[O.sub.2], based on comparison of the powder X-ray diffraction pattern of micro-crystalline co-type material with the pattern of a synthetic phase. Magnesium-zippeite contains zippeite-type uranyl sulfate sheets with Mg located between the layers, where it is in octahedral coordination. In Mg-zippeite, distorted Mg octahedra are linked by sharing vertices, resulting in dimers. The apices of the Mg octahedra correspond to two O atoms of uranyl ions, and four [H.sub.2]O groups. Magnesium-zippeite and marecottite co-exist, sometimes in the same sample, at Lucky Strike no. 2 mine, Emery County, Utah (type locality of Mg-zippeite), at Jachymov, Czech Republic, and at La Creusaz. This study provides insight into the complexity of the zippeite-group minerals containing divalent cations, where different arrangements in the interlayers result in different unit cells and space groups.

To better understand the extended X-ray absorption fine structure (EXAFS) spectroscopic information obtained for complex materials such as those encountered in Earth materials, we propose to use the Continuous Cauchy Wavelet Transform (CCWT). Thanks to this method, EXAFS spectra can be visualized in three dimensions: the wavevector (k), the interatomic distance uncorrected for phase-shifts (R'), and the CCWT modulus (corresponding to the continuous decomposition of the EXAFS amplitude terms). Consequently, more straightforward qualitative interpretations of EXAFS spectra can be performed, even when spectral artifacts are present, such as multiple-scattering features, multi-electronic excitations, or noise. More particularly, this method provides important information concerning the k range of each EXAFS contribution, such as next nearest-neighbors identification. To illustrate the potential of CCWT analyses applied to EXAFS spectra, we present experimental and theoretical spectra obtained for thorite and zircon at the Th [L.sub.II] and Zr K edges, respectively. Then, we present CCWT analyses of EXAFS spectra collected for amorphous materials of geochemical and environmental interest, including sodium trisilicate glass and an aqueous chloride solution, at the Mo K and Au [L.sub.III] edges, respectively. Further studies based on CCWT phase terms are underway, in order to quantitatively characterize anharmonic information from EXAFS contributions.

Cejkaite, a new mineral from Jachymov, NW Bohemia, Czech Republic, forms a thin earthy efflorescence over a calcite vein associated with disintegrated uraninite. The color is pale yellow to beige, the streak is light yellow, and the luster is vitreous. The broad secondary mineral association includes andersonite and schrockingerite. Chemical analysis (by ICP-MS and TG) gave (in wt%): [Na.sub.2]O = 21.39, MgO = 0.15, FeO = 0.53, U[O.sub.3] = 53.93, and C[O.sub.2] = 24.00 (calculated by difference). The simplified chemical formula is [Na.sub.4]U[O.sub.2][(C[O.sub.3]).sub.3]. The mineral is triclinic, space group P1 or P[bar]1, a = 9.291 (2), b = 9.292(2), c = 12.895(2) [Angstrom], [alpha] = 90.73(2), [beta] = 90.82(2), [gamma] = 120.00(1)[degrees], V = 963.7(4) [[Angstrom].sup.3], Z = 4, [D.sub.meas] = 3.67(1) g/[cm.sup.3], and [D.sub.calc] = 3.766(5) g/[cm.sup.3]. The strongest seven lines in the X- raypowder-diffraction pattern [d in [Angstrom](I)(hkl)] are: 8.022(92)([bar]110, 010, 100), 5.080(57)([bar]102, [bar]012), 5.024(60)([bar]112, [bar]112), 4.967(68)(012, 102), 4.639(100)([bar]120, [bar]210, 110), 3.221(63)(004), 2.681(60) ([bar]3.30, [bar]114, 030, 300). Optical data could not be measured due to the extremely small grain size, but the calculated mean refractive index is 1.5825. Crystal size varies from 0.2 to 0.6 [micro]m and shows an indistinct hexagonal outline. Thermal decomposition of synthetic cejkaite proceeds in three main steps. DTA endotherm at 430[degrees]C corresponds to the decomposition of the uranyl tricarbonate groups. IR spectrum of cejkaite confirms the presence of crystallographically nonequivalent [(C[O.sub.3]).sup.2-] groups and the absence of water. The average U-O bond length in [(U[O.sub.2]).sup.2+], calculated from [v.sub.3] = 848 [cm.sup.-1], is [R.sub.U-O] ~ 1.81 [Angstrom]. A model based on the crystal structure of trigonal [Na.sub.4](U[O.sub.2])[(C[O.sub.3]).sub.3] was adopted and applied to solve the cejkaite crystal structure by the Rietveld method (7238 unique reflections, [R.sub.p] = 0.076, [R.sub.wp] = 0.104). Uranium is eight-coordinated, and forms a [U[O.sub.2][O.sub.6]] skeleton with almost linear O-U-O that is roughly perpendicular to an irregular cycle formed by six O atoms that, in turn, belong to three more-or-less regular and planar C[O.sub.3] groups. Atoms Na1, Na1a, and Na2 are octahedrally coordinated, whereas [Na.sub.3] is pentagonally coordinated. The mineral name honors Jiri Cejka for his notable contributions to the crystal chemistry of U minerals.

Calcite aggregates are mineralized in an organic poly-acrylamide hydrogel using a counter diffusion arrangement. The particles obtained show a characteristic pseudo-octahedral morphology, which is unexpected for calcite crystals. Scanning and transmission electron microscopy reveal a microstructure composed of individual highly aligned calcite crystallites. Although the aggregates consist of independent crystallites, the X-ray diffraction patterns suggest calcite single crystals. By analogy with some biominerals, the inorganic assembly is intergrown with an organic hydrogel network. A specific model is proposed for growth of the aggregate.

Ideal pyroxenes are hypothetical structures based on ideal closest-packed arrangements of O anions. They are modeled after observed pyroxene structures and have the general formula M2M1[T.sub.2][O.sub.6], where M2 and M1 represent octahedrally coordinated cations, and T represents tetrahedrally coordinated cations. An algorithm has been created to construct all possible ideal pyroxenes based on closest-packed stacking sequences of length 12 or less. These structures are reported. The only significant structural parameters that vary between different ideal pyroxenes are the M1-T and M2-T distances. We show that the repulsive forces between these pairs of cations distinguishes the energetics of the ideal pyroxenes and may be important in determining the topologies of observed pyroxenes.

To establish more fully a basis for quantifying the role of apatite in trace-element fractionation processes, hitherto unknown mineral/melt partition coefficients ([D.sup.apatite/melt]) for a variety of trace elements (Li, Be, B, K, Cs, Rb, Ba, Th, U, Nb, Ta, La, Ce, Sr, Pr, Hf, Zr, Sm, Gd, Y, Lu, and Pb) have been measured between fluorapatite [[Ca.sub.5][([PO.sub.4]).sub.3]F], chlorapatite [[Ca.sub.5][([PO.sub.4]).sub.3]Cl], and hydroxylapatite [[Ca.sub.5][([PO.sub.4]).sub.3]OH] and carbonatite melt. Apatites were equilibrated experimentally with carbonatite melts at 1 GPa and 1250[degrees]C, and run products were analyzed for trace elements by secondary ion mass spectrometry (SIMS) and by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). Calculated partition coefficients indicate incompatibility of most analyzed elements. Rare-earth element (REE) partition coefficients show a convex-upward pattern, indicating that apatite prefers the middle (Sm, Gd) relative to the lighter (La, Ce, Pr) and heavier REE (Lu). Comparison of partition coefficients determined in this study with previous results in silicate systems reveals a strong influence of melt chemistry on partition coefficients, namely decreasing partition coefficients with decreasing silica-content, and increasing Ca and P in melts.

Titanium-rich biotites from graphite-bearing metapelitic xenoliths, equilibrated at ca. 850[degrees]C and 7 kbar in the presence of a granitic melt, have been studied through complete chemical analysis and single-crystal XRD refinements. The chemical study combines EMP analyses, hydrogen determination by both SIMS and C-H-N elemental analysis, and Mossbauer spectroscopy. Biotites in the analyzed xenoliths have Ti[O.sub.2] contents ranging from 4.5 to 4.9 wt% and an [X.sub.Fe] of 0.67. Their F and Cl contents are negligible, and [Fe.sup.3+]/[Fe.sub.tot] ranges from 10 to 16%. The [H.sub.2]O content of the biotites ranges from 2.4 to 2.8 wt%, and a small fraction of H is accommodated in the lattice as [NH.sub.4]. Based on these full chemical analyses, the calculated OH occupancy is 1.26 to 1.30 groups per formula unit, more than one third less than the stoichiometric value. The entrance of Ti in the octahedral site of biotite is consistent with the Ti-oxy exchange, whereas Ti-Tschermak or Ti-vacancy substitutions play a very minor role. The [Fe.sup.3+]-oxy exchange cannot account for the observed OH deficiency. From single-crystal XRD, biotites belong to the 1M polytype and contain variable amounts of stacking faults. The c cell parameter, K-O4 and [.sub.outer] distances provide an independent estimate of the OH content, which agrees with SIMS determinations. The linear relationship between [sup.VI][Ti.sup.4+] and the bond-length distortion of the cis-M2 octahedron reveals the partitioning of [Ti.sup.4+] in M2, and the [Ti.sup.4+] off-center shift toward O4 supports the occurrence of the Ti-oxy exchange. The ordering of [Ti.sup.4+] over two non-equivalent M2 sites, which would be favored energetically, is in agreement with the evidence for a third octahedral site suggested by Mossbauer spectroscopy. The biotite dehydrogenation combined with the partitioning of [Ti.sup.4+] in M2 and the low thermal expansion of [Ti.sup.4+]-containing octahedra, are the keys to understanding the thermal stabilization of Ti substitution in biotites.

The peak of regional metamorphism in western Maine was reached at ca. 404 Ma during the waning stage of Devonian Acadian deformation. Regional metamorphic mineral assemblages in metapelitic rocks range from greenschist to upper amphibolite facies. Subsolidus rocks are characterized by the association andalusite + staurolite; at the highest grades, anatectic migmatites are developed. Results of thermodynamic modeling in the MnNCKFMASH system are consistent with field data and imply a metamorphic field gradient that extends from 3.5-4.0 kbar at lower grades (500-520[degrees]C) to > 4.5 kbar at suprasolidus temperatures that exceeded 700[degrees]C. Regional isotherms that are inferred to have been shallowly inclined at lower grades are closely spaced around synmetamorphic granites and at the migmatite front, consistent with advection-controlled intracrustal redistribution of heat within the regionally extensive thermal high. Peak pressures vary both along and across the strike of the Central Maine belt, which is interpreted to record differential thickening during syntectonic metamorphism. Contact metamorphism associated with the Mooselookmeguntic igneous complex occurred ca. 35 million years after the regional metamorphic peak, and records higher pressure conditions than the regional event. We suggest that the final increment of late-Acadian thickening accounts for the pressure increase, consistent with regional cooling prior to the emplacement of the Mooselookmeguntic igneous complex. Pluton emplacement at deeper levels ca. 35 million years after the peak of Acadian metamorphism reflects lowering of the brittle-viscous transition zone, a level at which ascending magma is trapped, consequent on regional cooling and a steeper geotherm. An overall counter-clockwise P-T-t evolution is implied in the Central Maine belt, consistent with that proposed for Acadian metamorphism in western New Hampshire.

A critical aspect of the debate about the origin and conditions of metamorphism of the Alpe Arami (AA) peridotite is the disagreement over how much ilmenite is contained in the older generation of olivine and therefore how much Ti[O.sub.2] might have been dissolved at high pressure and temperature. We have now determined quantitatively the 3-dimensional distribution of ilmenite in AA olivine by confocal laser scanning microscopy (CLSM). The CLSM measurements show an average concentration of 0.31 vol% of ilmenite in olivine, with individual grains containing up to 1.2 vol%. This translates into average and maximum concentrations of 0.23 and 0.9 wt% Ti[O.sub.2] in olivine, respectively, and confirms the original estimation of maximum concentration of ~1 vol% Ti[O.sub.2]. The vast majority of ilmenite in AA olivine is distributed randomly (although topotactically oriented) and, in all cases, is accompanied by chromite in a ratio of ~4:1. These observations are consistent with an origin of the ilmenite (and chromite) by exsolution from an olivine solid solution at P = 9-12 GPa and temperatures above the stability field of titanian clinohumite, but are not consistent with suggested breakdown of titanian clinohumite. Combining these results with other recent findings suggests that exsolution followed deformation under relatively high fugacity of [H.sub.2]O, and that the high solubility of Ti[O.sub.2] is probably explained by pressure-induced accommodation of Ti in the tetrahedral site of silicates.

The low-frequency mechanical properties of polycrystalline [Ca.sub.1-x][Sr.sub.x]Ti[O.sub.3] (0.5 [less than or equal to] x [less than or equal to] 0.9) have been investigated as a function of temperature and bulk composition using the technique of dynamical mechanical analysis in three-point bend geometry. [Ca.sub.1-x][Sr.sub.x]Ti[O.sub.3] forms a cubic solid solution at high temperatures. At lower temperatures it undergoes successive displacive transitions to tetragonal and orthorhombic phases on cooling and increasing CaTi[O.sub.3] content. The low-frequency mechanical response of the tetragonal phase is dominated by thermally activated displacements of transformation twin domain walls, causing almost a twofold decrease in storage modulus relative to the twin-free cubic phase on cooling through the phase transition (superelastic softening). Below 140[degrees]C the mobility of domain walls decreases and the storage modulus returns to a value close to that of the cubic phase. For x > 0.85, the cubic to tetragonal transition temperature is below 140[degrees]C and domain walls are immobile immediately on formation, greatly reducing the magnitude of mechanical softening. The frequency dependence of the storage modulus is accurately described by a modified Burgers model of anelastic relaxation. Activation energies of 103 and 96 kJ/mol were obtained for samples with x = 0.7 and 0.74, respectively, suggesting that domain walls are strongly pinned by vacancies at the O positions. Superelastic softening is not observed below [T.sub.c] for the tetragonal to orthorhombic phase transition in samples with x = 0.5, 0.55, and 0.6. This is explained by the small value of the spontaneous strain in orthorhombic samples with intermediate compositions, which are distorted from cubic symmetry by less than 1[per thousand]. With such small strain contrast between differently oriented twin domains, the effective force on the domain walls due to the external stress is less than the critical unpinning force, preventing displacement of the walls and suppressing superelastic softening.

Chromian dissakisite-(Ce), a Cr-enriched Mg analogue of allanite-(Ce), is found in a garnet lherzolite from the Su-Lu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. Major minerals of the lherzolite are olivine [[X.sub.Mg] = Mg/(Mg + Fe) = 0.92], pyrope-rich garnet ([Prp.sub.70.1-73.2] [Alm.sub.11.3-13.4][Grs.sub.6.9-8.3]Uvr.sub.3.6-5.[Anr.sub.0-0.4][Sps.sub. 0.7-1.7]), orthopyroxene ([X.sub.Mg] = 0.92-0.93), and clinopyroxene (X.sub.Mg = 0.92-0.95). The chromian dissakisite-(Ce) occurs as a single-crystal inclusion in a clinopyroxene neoblast that also contains several irregularly shaped olivine grains. It is partly metamict, and there is intensive radial cracking in the surrounding clinopyroxene. Its composition is represented by the averaged formula: [([Ca.sub.0.86][Na.sub.0.03]).sub.0.89][([REE.sub.0.86] [Th.sub.0.04]).sub.0.90] ([Mg.sub.0.98][Fe.sup.2+sub.0.20][Fe.sup.3+.sub.0.21] [Cr.sub.0.36][Al.sub.1.39] [Ti.sub.0.04])[Si.sub.3.03][O.sub.12](OH), with [Ce.sub.2][O.sub.3], MgO and [Cr.sub.2][O.sub.3] contents up to 13.1, 7.3, and 5.4 wt%, respectively. Because the M3 site in the chromian dissakisite-(Ce) is fully occupied by Mg and [Fe.sup.2+]., [Fe.sup.3+] and Cr can only occupy the smaller M1 site. Similar site occupancy is noted for a chromian allanite from the Sanbagawa metamorphic belt, Japan, which contains up to 0.547 Cr atoms per formula unit (apfu). Such compositional characteristics of the chromian dissakisite/allanite and existing polarized absorption data on Cr-bearing epidote suggest the existence of possible end-members, 'CeCa(Mg,Fe)CrAl[Si.sub.3][O.sub.12](OH),' for the epidote-group minerals, which may form solid solution with [Ca.sub.2][Al.sub.3][Si.sub.3][O.sub.12](OH) through coupled substitutions of REEMg[Ca.sub.-1][Al.sub.-1], REEFe[Ca.sub.-1][Al.sub.-1], and Cr[Al.sub.-1]. The rare earth elements (REE), Ca, and Na total 1.79 apfu, implying that Mn and [Fe.sup.2+] are also present on the nine-coordinated Al site. The high REE abundance, the presence of minor Na, and the Mg and Cr-enriched characteristics of the mineral suggest that it was formed as a result of reaction between the host lherzolite and crustderived melt/fluid at UHP conditions. Textural relations suggest that the chromian dissakisite-(Ce) was unstable in the garnet lherzolite and reacted with olivine to form clinopyroxene, Dissakisite(REE) in subducted ultramafic rocks can transport rare earth elements into the Earth's mantle.

A new series of aluminogermanate alkali feldspars has been synthesized as part of a study to investigate elastic strain energies in exsolved samples. Enthalpies of solution in 20.1 wt% hydrofluoric acid (Hr) at 50[degrees]C for chemically homogeneous unstrained members of this series can be expressed as a function of mole fraction K ([N.sub.OrGe]): -[H.sub.soln] (kJ/mol) = 630.65 + 9.92 [N.sub.OrGe] - 47.0 [N.sup.2.sub.OrGe] + 17.6 [N.sup.3.sub.OrGe]. The associated enthalpies of mixing, [H.sub.ex] (kJ/mol) = 29.4 [N.sub.OrGe] + [N.sup.2.sub.AbGe] + 11.9 [N.sub.AbGe] [N.sup.2.sub.OrGe] (where [N.sub.abGe] is mole fraction Na), reach maximum values of 5.4 kJ/mol at sodic compositions, similar in behavior to normal aluminosilicate analogs. Enthalpies of elastic strain associated with exsolution have been determined via HF solution calorimetric experiments on several coherently exsolved samples of the aluminogermanate series and also on a normal Ge-free aluminosilicate alkali feldspar. These energies were found to be less than 2.0 kJ/ mol, consistent with independent estimates by previous workers.

Molecular structures of the basic copper arsenate minerals olivenite, cornubite, cornwallite, and clinoclase were studied using a combination of infrared emission spectroscopy and Raman spectroscopy. Infrared emission spectra of the basic copper arsenates were obtained over the temperature range 100 to 1000[degrees]C. The IR emission spectra of the four minerals are different, in line with differences in crystal structure and composition. The Raman spectra are similar, particularly in the OH-stretching region, but characteristic differences in the deformation regions are observed. Differences are also observed in the arsenate stretching and bending regions. Infrared emission studies show that the minerals are completely dehydroxylated by 550[degrees]C.

Zinc speciation was studied by EXAFS spectroscopy, [micro]-SXRF elemental mapping, XRD, and chemical extraction methods in two smelter-impacted soils sampled near one of the largest Pb and Zn processing plants in Europe, which is located in northern France about 50 km south of Lille. The tilled and wooded soils chosen for study differ in Zn concentration ([approximately equal to]600 and 1400 mg/kg, respectively), soil pH (7.5 and 5.5, respectively), and organic matter content (1.5 and 6.4 wt% TOC, respectively). In both soils, the occurrence of Fe- and Zn-rich (up to 10 wt% Zn) slag particles ranging in size from a few micrometers to a few millimeters, was shown by [micro]-SXRF elemental mapping of soil thin sections as well as by SEM and chemical analysis of different soil size fractions. For both soils, XRD analysis of the dense coarse fraction, which contains up to 10 wt% Zn, revealed the presence of a minor amount (1-1.5 wt%) of crystalline ZnS (sphalerite and wurtzite). In this fraction, EXAFS data show that Zn is mainly incorporated in the tetrahedral sites of a magnetite-franklinite solid solution. The clay fraction (

Room-temperature FTIR spectra of ten chemically and structurally well-characterized synthetic spinel-hercynite solid solution single crystals containing between 4 and 98 mol% hercynite component show that absorption in the range 2500-7000 [cm.sup.-1] is linearly correlated ([R.sup.2] = 0.995) with [sup.IV][Fe.sup.2+] concentration. The integral molar absorption coefficient for this absorption equals 1.49.[10.sup.8] em/mol. In addition, the structure of the absorption envelope in this spectral region remains unchanged throughout the entire composition range. These two findings are consistent with assignments to a spin-allowed electronic d-d transition ([sup.5]E [right arrow] [sup.5][T.sub.2]) in [sup.IV][Fe.sup.2+], split by the dynamic Jahn-Teller effect, and demonstrate that next-nearest interactions in Fe clusters have little or no effect on this absorption feature at ambient conditions.

The Fe end-members scorzalite [[Fe.sup.2+][Al.sup.3+.sub.2][([PO.sub.4]).sub.2][(OH).sub.2]] and barbosalite [[Fe.sup.2+][Fe.sup.3+.sub.2][([PO.sub.4]).sub.2][(OH).sub.2]] of the lazulite series have been investigated by Mossbauer and diffuse reflectance spectroscopy, and by electronic structure calculations in the local spin density approximation. The measured quadrupole splitting ([[DELTA]E.sub.Q] = -3.99 mm/s) in scorzalite is in quantitative agreement with the calculated value ([[DELTA]E.sub.Q] = -3.90 mm/s), as well as its temperature dependence. The optical spectrum of barbosalite can be resolved into three peaks at 8985 [cm.sup.-1], 10980 [cm.sup.-1], and 14110 [cm.sup.-1]. These positions correlate well with the two calculated spin-allowed d-d transitions at 8824 [cm.sup.-1] and 11477 [cm.sup.-1], and with an intervalence charge transfer transition at about 14200 [cm.sup.-1]. The calculated low-temperature magnetic structure of barbosalite is characterized by a strong antiferromagnetic coupling (J = -84.6 [cm.sup.-1]) within the octahedral [Fe.sup.3+]-chains, whereas a weak antiferromagnetic coupling within the trioctahedral subunit cannot be considered as conclusive. The analysis of the charge and spin densities reveals that more than 90% of the covalent part of the iron-ligand bonds arises from the Fe(4s,4p)-electrons. Clusters of at least 95 atoms are required to reproduce the available experimental data with quantitative accuracy.

The layer silicates are among the most common minerals in the Earth's surface environment, play important roles in many geological processes, and have diverse technological applications. While it has been suggested that O isotope exchange and dissolution kinetics in aqueous solutions are controlled by chemical bonding and local atomic structures, the effect of atomic environment around O atom sites in clay minerals on their site-specific reactivities with [H.sub.2]O are not well known, mainly because direct experimental evidence is lacking. Here, we present for the first time detailed high-resolution [sup.17]O NMR data for [sup.17]O-exchanged natural kaolinite [[Al.sub.2][Si.sub.2][O.sub.5][(OH).sub.4]] and muscovite [[KAl.sub.2]([AlSi.sub.3])[O.sub.10][(OH).sub.2]] using [sup.17]O triple quantum magic angle spinning (3QMAS) and MAS NMR at high fields. At least two basal O atom sites in kaolinite are resolved: 04, and (03 + 05). Apical O atoms ([sup.[4]]Si-O-2[sup.[6]]Al) and hydroxyl groups are also shown in these spectra. The [sup.17]O 3QMAS spectrum for muscovite shows improved resolution over the [.sup.17]O MAS NMR spectrum, allowing us to resolve several basal O atoms, including ([sup.[4]Si-O[sup.[4]Al), as well as hydroxyl groups. The fraction of each O atom appears to deviate somewhat from the stoichiometric value, suggesting that each crystallographically distinct site may have a different rate of exchange with the O atom in [H.sub.2]O.

Single-crystal X-ray diffraction data, collected from a sartorite crystal from Lengenbach (Binntal, Valais, Switzerland), yielded a ninefold superstructure: space group P[2.sub.1]/c; a = 37.71 (2), b = 7.898(3), c = 20.106(8)[Angstrom] [beta] = 101.993(7)[degrees]; [R.sub.1] = 6.08% for 6293 reflections with I > 2[[sigma].sub.I]. The sample is an [N.sub.1,2] = 3,3 sartorite homologue and the refined formula [Pb.sub.8][Tl.sub.1.5][As.sub.17.5][S.sub.35] compares very well with the empirical formula [Pb.sub.8.2][Tl.sub.1.4][As.sub.17.5][Sb.sub.0.5][S.sub.35] obtained from electron microprobe analyses. It has a high T1 content, up to 6.5 wt%. In a coupled substitution approximately 1.5 [Tl.sup.+]replace about 0.5 [As.sup.3+] and 1 PbS. The refined structure has 35 S atoms pfu instead of the expected 36 S (= 9 x 4 S, from Pb[As.sub.2][S.sub.4]). The incorporation of substantial amounts of [Tl.sup.+] into Pb[As.sub.2][S.sub.4]) is essential for the type and periodicity of superstructures in sartorite. The refined superstructure can be interpreted as a so-called 'lock-in' structure with a composition that yields a commensurate lattice for a mineral that usually has an incommensurate lattice. No commensurate periodicity could be found for a second crystal with about 0.5 Tl apfu.

The magnetic microstructure of a natural, finely exsolved intergrowth of submicron magnetite blocks in an ulvospinel matrix is characterized by using off-axis electron holography in the transmission electron microscope. Single-domain and vortex states in individual blocks, as well as magnetostatic interaction fields between them, are imaged at a spatial resolution approaching the nanometer scale. The images reveal an extremely complicated magnetic structure dominated by the shapes of the blocks and magnetostatic interactions. Magnetic superstates, in which clusters of magnetite blocks act collectively to form vortex and multidomain states that have zero net magnetization, are observed directly.

The favorable spin arrangement between adjacent layers of CuO(sub)2 ribbon chains in the Cu(sub)2O(sub)3 spin lattice of paramelaconite forces the CuO(sub)2 chains to adopt an infinite opposing spin exchange arrangement. Data indicate that the calculated spin exchange parameters suggest a low-dimensional magnetic character determines the magnetic properties of paramelaconite.

X-ray diffraction experiments have been carried out on [beta]-eucryptite (LiAlSi[O.sub.4]) at pressures up to 2.5 GPa and temperatures up to 1073 K in a large-volume apparatus. With room-temperature compression, we observed a phase transition to a new polymorph between 0.83 and 1.12 GPa. This transition is reversible in character. The new phase, referred to here as [epsilon]-eucryptite, can be indexed according to an orthorhombic unit cell with a = 10.217(4) [Angstrom], b = 8.487(4), [Angstrom] c = 5.751(3) [Angstrom], and V = 498.7(4) [[Angstrom].sup.3] for XRD data at 2.2 GPa and 298 K. On heating at 2.2 GPa, [epsilon]-eucryptite and [beta]-eucryptite were metastable over the temperature interval 298-873 K; at higher temperatures they underwent an irreversible phase transition to [alpha]-eucryptite. Both hexagonal [alpha]-eucryptite and [epsilon]-eucryptite show anisotropic thermal expansion. For [alpha]-eucryptite, we obtained [[alpha].sub.a] = 6.71([+ or -]0.25) x [10.sup.-6] [K.sup.-1], [[alpha].sub.c] = 1.07([+ or -]0.05) x [10.sup.-5] [K.sup.-1], and [[alpha].sub.v] = 2.42([+ or -]0.1) x [10.sup.-5] [K.sup.-1] at 1.94(2) GPa over the temperature range 298-1073 K, For [epsilon]-eucryptite at 2.32(8) GPa, we find larger thermal expansion in a smaller temperature range 298-773 K, with [[alpha].sub.a] = 1.47([+ or -]0.15) x [10.sup.-5] [K.sup.-1], [[alpha].sub.b] = 6.65([+ or -]1.33) x [10.sup.-6] [K.sup.-1], [[alpha].sub.c] = 7.83([+ or -]0.88) x [10.sup.-6] [K.sup.-1], and [[alpha].sub.v] = 2.99([+ or -]0.15) x [10.sup.-5] [K.sup.-1]. In combination with a previous determination of thermal expansion at ambient pressure, the pressure effect on volume thermal expansion of [alpha]-eucryptite is determined to be -2.68 x [10.sup.-6] [GPa.sup.-1] [K.sup.-l], and the temperature derivative of the bulk modulus is estimated to be -0.015 GPa/K.

Significant amounts of boron in both trigonal and tetrahedral coordination have been found through [sup.11]B magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of natural olenite (aluminum-rich tourmaline) from Stoffhutte, Koralpe, Styria, Austria. The [sup.11]B MAS NMR spectrum consists of a superposition of two quadrupolar MAS peaks. A broad peak with [[delta].sub.iso] = 18.3 ppm, [v.sub.Q] = 1410 KHz, and [eta] = 0.11 demonstrates the trigonal-planar environment of the B[O.sub.3] group (relative area ratio = 80%). The narrow symmetrical peak ([[delta].sub.iso] = 0.0 ppm, [v.sub.Q] = 300 KHz, [eta] = 0.00) represents tetrahedral B[O.sub.4] groups (relative area ratio = 20%). An infrared spectrum shows hydroxyl stretching bands at low wavenumbers indicating that underbonded O atoms of the hexagonal ring (due to a partial replacement of [sup.[4]][Si.sup.4+] by [sup.[4]][B.sup.3+]) form relatively strong hydrogen bonds with the protons of the hydroxyl groups. A [sup.29]Si MAS NMR spectrum shows a peak consisting of a main signal at -90 ppm and a shoulder at about -85 ppm. The main signal originates from Si atoms connected (via oxygen bridges) to two other Si atoms in the hexagonal ring, and the minor signal is from Si atoms connected to one Si and one B atom. No signal corresponding to [sup.[6]]Si was detected in this natural olenite sample.

Hogbomite is a closest-packed polysomatic mineral composed of spinel, [T.sub.2][M.sub.4][O.sub.8], and nolanite-like, [TM.sub.4][O.sub.7](OH), modules where T stands for tetrahedrally and M for octahedrally coordinated cations. The modules are stacked in an ordered fashion in various ratios. Single-crystal X-ray diffraction for a 24R and a 10T polysome and structure modeling for a 12H and 14T polysome have been applied to characterize different stacking variants. Hogbomite from a spinel-phlogopite schist at Corundum Creek (South Australia) with composition [Mg.sub.3.8][Fe.sub.3.2][Zn.sub.1.6][Ti.sub.1.0][A1.sub.18.3][0.sub.38] [(OH).sub.2] is a 10T polysome with a = 5.723(1), c = 23.026(4) [Angstrom], space group P[bar]3ml, Z = 1. This polysome with the general formula [T.sub.8][M.sub.20][0.sub.38][(OH).sub.2] is composed of an alternation of spinel (S) and nolanite-like (N) blocks stacked in the sequence NSSNS. Hogbomite from a Fe-Ti deposit at Liganga (Tanzania) with composition [Mg.sub.13.5][Fe.sub.5.6][(Zn,Mn,Ni).sub.0.2] [Ti.sub.4.7][Al.sub.41.7][(Cr, Ga).sub.0.2][0.sub.90][(OH).sub.6] is a 24R polysome with a = 5.7145(7), c = 55.056(5) [Angstrom], space group R[bar]3m, Z = 1. The structure with the general formula [T.sub.18][M.sub.28][O.sub.90][(OH).sub.6] is composed of a periodic alternation of two S and two N blocks. The crystal structures of hogbomite-12H, [T.sub.10][M.sub.24][0.sub.46][(OH).sub.2], a = 5.7, c = 27.6 [Angstrom], space group [P6.sub.3]mc, Z = 1, and hogbomite-14T, [T.sub.12][M.sub.28][0.sub.54][(OH).sub.2], a = 5.7, c = 32.2 [Angstrom], space group P[bar]3ml, Z = 1, were modeled from the stacking principles of the known 6T, 8H, 10T, and 16H polysomes. The 12H and the 14T polysomes have stacking sequences NSSNSS and NSSSNSS, respectively.

The incorporation of molecular water into the c-parallel structural channels in end-member beryl [sup.VI][Al.sub.2] [[Be.sub.3][Si.sub.6][O.sub.18]] * n[H.sub.2]O, where [n.sub.[H.sub.2]O] = 1.00 corresponds to 3.24 wt% [H.sub.2]O, was studied experimentally in the temperature-pressure range 400-950 [degrees] C and 1-14.5 kbar ([P.sub.[H.sub.2]O]= [P.sub.tot]). Time-dependent studies ensured that the incorporation of water by beryl had reached the equilibrium [n.sub.[H.sub.2]O] values in thehydration experiments. Increasing water contents were found to enhance the refractive indices of beryl as follows: [n.sub.[epsilon]] = 1.5585 + 0.0080 * wt% [H.sub.2]O (r = 0.986) [n.sub.[omega]] = 1.5616 + 0.0086 * wt% [H.sub.2]O (r = 0.978) These relations were used to determine the water contents attained in the equilibrium experiments, and were calibrated using synthetic beryls, the water contents of which had been determined gravimetrically with an accuracy of [+ or -] 0.06 wt% [H.sub.2]O. The incorporation of water into the structural channels of beryl leaves the hexagonal a-axis unchanged, a = 9.2110(10) [Angstrom], c and V increase as: c ([Angstrom]) = 9.1893 + 0.0020 * wt% [H.sub.2]O (r = 0.974) V ([[Angstrom].sup.3]) = 674.98 + 0.203 * wt% [H.sub.2]O (r = 0.936) Two isobars at 3.4 and 10.8 kbar with [P.sub.[H.sub.2]O] = [P.sub.total] could be modeled as: wt% [H.sub.2]O (P) = a - bT ([degrees] C) + c[T.sup.2] ([degrees] C) 3.4 kbar: a = 4.10, b = 5.90 * [10.sup.-3], c = 0.31 * [10.sup.-5] (r = 0.963) 10.8 kbar: a = 3.31, b = 0.514 * [10.sup.-3], c = 0.00 (r = 0.941) Similarly, the two isotherms at 600 and 900 [degrees] C could be modeled as: wt% [H.sub.2]O (T) = a + bP (kbar) - c[P.sup.2] (kbar) 500 [degrees] C: a = 0.94, b = 0.261, c = 0.0075 (r = 0.949) 900 [degrees] C: a = 0.19, b = 0.331, c = 0.0092 (r = 0.964) These relations together with data points from additional experiments were used to construct a ([P.sub.[H.sub.2]O = [P.sub.tot]) - T field of isohydrons for the system end-member beryl-[H.sub.2]O. Comparing [n.sub.[H.sub.2]O]-P sections at 600 [degrees] C for beryl obained in this study with data for Mg-cordierite obtained from the literature, proves nearly the same equilibrium contents of water in both minerals.

The proton positions in leucophoenicite, ideally [Mn.sub.7][Si.sub.3][O.sub.12][(OH).sub.2], have been determined by neutron powder diffraction under ambient conditions on a natural sample from Franklin, New Jersey. Refinement in the P[2.sub.1]/a space group gave [R.sub.p] = 2.0% (w[R.sub.p] = 2.1%), [chi square] = 4.04 for 110 refined parameters. The two non-equivalent protons form a pair of hydroxyl groups and make hydrogen bonds to the same O7 atom of the Si1 tetrahedron at distances of 1.99(1) and 2.09(1) [Angstrom]. The H.... H distance in leucophoenicite is 2.16(1) [Angstrom], which is more than twice the Van der Waal's radius of H (>2 [Angstrom]) and so no proton positional disorder is expected in leucophoenicite. A comparison of the H environments is made between leucophoenicite and Phase B, Superhydrous B, and Phase A.

A procedure was developed for accurate quantification of REE, actinides, and light elements in complex matrixes of interest in earth and material sciences (hellandite and britholite, the REE analogue of apatite). These minerals show a peculiar chemical composition due to the coexistence of high amounts of LREE, U, Th with variable quantities of H, Li, Be, B, and F. Molecular interferences were resolved, and problems arising from unpredictable matrix effects and lack of reference materials were overcome. X-ray single-crystal structure refinement (SREF), which is not affected by matrix effects and does not require analytical standardization, was used to precisely estimate (by means of both site-scattering value and site geometry) in a wholly independent way the amounts and the distribution of the various groups of elements. The combined SIMS-SREF approach allowed us to obtain results of impact for mineralogy and also allowed the accuracy of SIMS investigation to be fixed. The capabilities of SIMS in the quantification of light (Z 57) elements as both minor and major constituents ((mathematical expression not reproducible in ASCII)REE(sub ox)) up to approximately 70 wt % in britholite) are shown. This approach may open new perspectives for the in situ analysis of chemically complex materials.

Thermal expansivities for the MgSiO(sub 3) phases of orthoenstatite, high clinoenstatite, ilmenite, and majorite; and for stishovite were estimated using the thermodynamic Maxwell relation (mathematical expression not reproducible in ASCII) = (mathematical expression not reproducible in ASCII) where the entropies at high pressures were derived using a statistical method and spectroscopic data. The spectroscopically determined thermal expansivities for all minerals are in excellent agreement with previously determined volumetric data, where available. A value of 3.25(10) X 10(super -5) K(super -1) for orthoenstatite at room temperature was obtained; this value is situated in the middle of the large spread of reported values and is in excellent agreement with the two latest volumetric determinations. For high clinoenstatite, (alpha) at room T is estimated as 2.56(9) x 10(super -5) K(super -1). This method provides good high temperature estimates of (alpha) for the high-pressure polymorphs, where data are scanty or unavailable. Included in this report are previous data for the Mg(sub 2)SiO(sub 4) phases and MgO for completeness. The following equations may be used to extrapolate a to higher temperatures at 1 atm in 10(super -5) K(super -1): (alpha)(majorite) = 2.95 + 0.000521x; (alpha)(gamma)-Mg(sub 2)SiO(sub 4) = 2.70 + 0.000648x; (alpha)(ilmenite) = 2.64 + 0.000537x; (alpha)(perovskite) = 2.51 + 0.000805x; and (alpha)(stishovite) = 2.19 + 0.000485x, where x is (T/K-750).

Ultrahigh-pressure (UHP) minerals of the Maowu mafic-ultramafic complex in the Dabieshan, east-central China exhibit many exsolution textures. Magnetite lamellae are common in olivines and Ti clinohumites from harzburgite and garnet pyroxenite. Monazite-(Ce) lamellae occur in apatites from the garnet pyroxenite. Independent P-T estimates suggest that these ultramafic rocks formed at P > 5 GPa and T = 700 [+ or -] 50 [degrees] C. The lamellae-bearing minerals are believed to preserve an earlier, higher P-T record prior to exsolution. Compositions and unit-cell parameters of the magnetite and host olivine and intergrowth relations were determined using a newly developed X-ray diffraction microprobe technique employing synchrotron radiation. The host olivine and magnetite lamellae bear a topotaxial relation with [[220].sub.Mag] || [[200].sub.Ol], [[111].sub.Mag] || [Mathematical Expression Omitted], [Mathematical Expression Omitted] || [[331].sub.Ol], [[242].sub.Mag] || [Mathematical Expression Omitted]. The recalculated composition of primary olivine may contain up to 1.5 wt% [Fe.sub.2][O.sub.3]. Four hypotheses may explain the observed intergrowths of oriented magnetite lamellae in olivine: (1) oxidation of olivine; (2) decomposition of [Fe.sup.3+]-bearing olivine formed at >6 GPa; (3) exsolution of a spinel (wadsleyite) solid-solution [Fe.sub.3][O.sub.4]-[(Fe,Mg).sub.2]Si[O.sub.4] during decompression; and (4) breakdown of phase A [[Mg.sub.7][Si.sub.2][(OH).sub.6]] + enstatite. The third hypothesis appears to be the most likely inasmuch as no additional silicate phase occurs as associated inclusions in the olivine host. However, the actual mechanism for exsolution of magnetite from olivine remains to be studied experimentally.