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Hydrous wadsleyite ([beta]-[Mg.sub.2]Si[O.sub.4]) with 2.8 wt% water content has been synthesized at 15 GPa and 1250[degrees]C in a multi-anvil press. The unit-cell parameters are: a = 5.6686(8), b = 11.569(1), c = 8.2449(9) [Angstrom], [beta] = 90.14(1)[degrees], and V = 540.7(1) [[Angstrom].sup.3], and the space group is I2/m. The structure was refined in space groups Imma and I2/m. The room-pressure structure differs from that of anhydrous wadsleyite principally in the increased cation distances around O1, the non-silicate oxygen. The compression of a single crystal of this wadsleyite was measured up to 61.3(7) GPa at room temperature in a diamond anvil cell with neon as pressure medium by X-ray diffraction at Sector 13 at the Advanced Photon Source, Argonne National Laboratory. The experimental pressure range was far beyond the wadsleyite-ringwoodite phase-transition pressure at 525 km depth (17.5 GPa), while a third-order Birch-Murnaghan equation of state (EoS) [[V.sub.0] = 542.7(8) [[Angstrom].sup.3], [K.sub.TO] = 137(5) GPa, K' = 4.6(3)] still fits the data well. In comparison, the second-order fit gives [V.sub.0] = 542.7(8) [[Angstrom].sup.3], [K.sub.T] = 147(2) GPa. The relation between isothermal bulk modulus of hydrous wadsleyite [K.sub.TO] and water content [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is: KTO = 171 ( 1)-12(1 ) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (up to 2.8 wt% water). The axial-compressibility [[beta].sub.c] is larger than both [[beta].sub.a] and [[beta].sub.b], consistent with previous studies and analogous to the largest coefficient of thermal expansion along the c-axis. Keywords: Compressibility, hydrous wadsleyite, neon, orthorhombic DOI: 10.2138/am.2010.3533

The crystal structure and crystal chemistry of chromian pumpellyite from basic schist in the Osayama ultramafic body, Okayama, Japan, were investigated using electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), and single-crystal X-ray diffraction to determine the distribution of chromium between two independent octahedral sites and structural changes caused by ionic substitutions in pumpellyite, [sup.VII][W.sub.8][sup.VI][X.sub.4][sup.VI][Y.sub.8] [sup.IV][Z.sub.12][O.sub.56-n],[(OH).sub.n], (Z = 1). Five cbromian pumpellyite crystals (ocpl211, ocp0604, ocp1028, ocpl013, and ocpl016) with 0.52, 1.65, 1.26, 1.94, and 1.43 Cr atoms per formula unit (apfu) (EPMA data), respectively, were picked from a hand specimen for X-ray diffraction analysis. The crystal structures (space group C2/m) of ocp1211 [a = 19.1129(6), b = 5.8963(5), c = 8.818(1) [Angstrom],[beta] = 97.449(2)[degrees]], ocp0604 [a = 19.0935(4), b = 5.900(1), c = 8.810(2) A, [Angstrom],[beta] = 97.540(7)[degrees]], ocp1028 [a = 19.105(2), b = 5.9021(6), c = 8.8143(7) [Angstrom], [beta] = 97.513(3)[degrees]], ocp1013 [a = 19.1558(6), b = 5.9125(9), c = 8.844(1) [Angstrom], [beta] = 97.448(4)[degrees]], and ocp1016 [a = 19.174(3), b = 5.9194(8), c = 8.830(1) [Angstrom], [beta] = 97.497(4)[degrees]] were refined using 1058, 829, 1070, 1105, and 1095 unique reflections, and calculations converged at R factors of 4.08, 5.02, 6.32, 6.92, and 7.88%, respectively. The resulting site populations at the X and Y sites are [([Mg.sub.1.88][Al.sub.1.51] [Fe.sup.2+.sub.0.38] [Cr.sub.0.16][Mn.sup.2+.sub.0.05][Ni.sub.0.02]).sup.X] [([Al.sub.7.90][Ti.sub.0.07][V.sub.0.03]).sup.Y] for ocp1211, [([Mg.sub.1.81][Al.sub.1.53][Cr.sub.0.42][Fe.sup.2+.sub.0.18] [Mn.sup.2+.sub.0.04][Ni.sub.0.01]).sup.X][([Al.sub.7.34] [Cr.sub.0.65][V.sub.0.01]).sup.Y]for ocp0604, [([Al.sub.1.62] [Mg.sub.1.60][Cr.sub.0.61][Fe.sup.2+.sub.0.13][Mn.sup.2+.sub.0.03] [Ni.sub.0.01]).sup.X][([Al.sub.7.36][Cr.sub.0.61][V.sub.0.03]).sup.Y] for ocp1028, [([Mg.sub.1.79][Al.sub.1.33][Cr.sub.0.47] [Fe.sup.2+.sub.0.33][Mn.sup.2+.sub.0.08]).sup.X] ([Al.sub.1.62][Mg.sub.1.60][Cr.sub.0.61][Fe.sup.2+.sub.0.13][Mn.sup.2+. sub.0.03][Ni.sub.0.01]).sup.X]) [([Al.sub.7.36][Cr.sub.0.61][V.sub.0.03]).sup.Y] for ocp1016. [Cr.sup.3+] ions in ocp 1211 are distributed only in the X site. The distribution coefficient of Cr and Al between the X and Y sites [[(Cr/A1).sup.x]/[(Cr/Al).sup.Y]] is 1.66, 1.79, 3.09, and 4.54 for ocp1016, ocp1013, ocp0604, and ocp1028, respectively, indicating a stronger preference of Cr for the X site than the Y site. The a and b axes increase with increasing Cr content, whereas the c axis is almost constant. The mean Y-O distances increase linearly with increased [Cr.sup.3+] content in the Y site. However, the mean X-O distances do not depend on the substitution of [Cr.sup.3+] for [Al.sup.3+] at the X site. The bond valence sums and the difference-Fourier synthesis indicate that hydroxyl groups are located at the 05, 07, O10, and O11 positions. FTIR spectrum shows main absorption bands at ca. 2911, 3220, 3397, and 3512 [cm.sup.-1] of OH-stretching vibrations, indicating the presence of OH ... O hydrogen bonds. Keywords: Pumpellyite, chromium, X-ray structural analysis, crystal chemistry, FTIR DOI: 10.2138/am.2010.3376

Natural kaolin, from Fujian province in China, was used as raw material to synthesize zeolite 4A powder under low-temperature hydrothermal treatment in alkali solution. Optimization studies on various reaction parameters were conducted. With the addition of an inorganic binder (montmorillonite), the as-prepared powder was shaped into spheres for desiccant application in industrial fields. Zeolite 4A powder was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the obtained powder was a cubic phase with high crystallinity. The water sorption capacity (WSC) and final compression strength (FCS) of zeolite 4A desiccant were studied. Higher crystallinity of zeolite 4A powder led to the higher WSC of zeolite desiccant. The observed WSC and FCS of 21.0% and 44.8 N, respectively, confirmed the potential application of zeolite 4A for water sorption. Keywords: Zeolite 4A, desiccant, kaolin, water sorption capacity (WSC), final compression strength (FCS) DOI: 10.2138/am.2010.3288

Crystals of the solid-solution series of (Ca,Sr)-lawsonite were synthesized hydrothermally at 4 GPa and 600 and 800[degrees]C in piston-cylinder experiments. Synthesis products were analyzed with SEM, EMP, and powder-XRD. Lawsonite was observed in both the orthorhombic space group Cmcm and in the monoclinic space group [P2.sub.1]/m. It is exclusively orthorhombic at low [x.sup.bulk.sub.Sr] but monoclinic at high [x.sup.bulk.sub.Sr]; in the range [x.sup.bulk.sub.Sr] = 0.18 to 0.4 both polymorphs coexist and the data suggest a two- phase field between X.sup.ortho.sub.Sr] ~0.1-0.2 and [x.sup.mono.Sr] ~0.3-0.4 at 4 GPa/600[degrees]C. Linear regression to the refined lattice parameters yields a = 0.017 X [X.sup.Sr] + 5.841 ([Angstrom]), b = 0.197 x [X.sub.Sr] + 8.787 ([Angstrom]), c = 0.263 x [x.sub.Sr] + 13.130 ([Angstrom]), and v 4.62 x [x.sub.Sr] + 101.46 ([cm.sup.3]/mol) for orthorhombic lawsonite and a = 0.119 x [x.sub.Sr] + 5.306([Angstrom]), b = 0.118 x [x.sub.Sr] + 13.160 ([Angstrom]), C = 0.025 x [x.sub.Sr] + 5.833 ([Angstrom]), [beta] = 0.38 x [x.sub.Sr] + 124.07 ([sup.o]), and v 3.20 x [x.sub.Sr] + 101.59 ([cm.sup.3]/mol) for monoclinic lawsonite. The data suggest an increasingly negative [[DELTA]v.sub.ortho-mono] with increasing [x.sub.Sr]. In monoclinic lawsonite, structural expansion due to the incorporation of Sr is primarily accomplished by tilting and rotation within the [Si.sub.2][O.sub.7]-group, whereas in orthorhombic lawsonite this tilting and rotation is prohibited by symmetry restrictions and expansion is mostly accomplished by an increase in lattice parameters. Combining the extrapolated Ca end-member volume for monoclinic lawsonite with published high-P data yields [K.sup.mono.sub.0] = 137(3) GPa (K' = 4.4). Contrary to the Ca end-member system, the Cmcm--[P2.sub.1]/m phase transition is quenchable within the Sr-bearing system. A tentative phase diagram for (Ca,Sr)-lawsonite at 600[degrees]C indicates a narrow orthorhombic-monoclinic two-phase field that shifts significantly to lower pressure with increasing Xs~. The Cmcm--[P2.sub.1]/m phase transition in the Sr end-member system is located at [less than or equal to] 1 GPa at ~400 to 600[degrees]C, 6 to 9 GPa below the transition in the Ca-system, and has a negative P-T slope. Keywords: Crystal structure, lawsonite, XRD data, experimental petrology DOI: 10.2138/am.2010.3220

The response of the mesolite crystal structure ([Na.sub.16][Ca.sub.16][Al.sub.48][Si.sub.72][O.sub.240] x 64 [H.sub.2]O) to dehydration was evaluated as a function of temperature and partial pressure of water (i.e., [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] or relative humidity, RH) using laboratory X-ray powder diffraction (XRD; CuK[alpha] radiation) and synchrotron X-ray pair distribution function (PDF) methods. At 425[degrees]C under low-[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] conditions ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] [less than or equal to] ~1.3 mbar), dehydrated mesolite preserved the long-range ordered aluminosilicate framework structure, which has not been previously observed. This new dehydrated phase, x-metamesolite, has unit-cell parameters [a 16.731(3) [Angstrom], b = 17.822(2) [Angstrom], c = 6.312(1) [Angstrom], V 1882.5(5) [[Angstrom].sup.3], and possible space group Fdd2] similar to those of other dehydrated natrolite phases (either [alpha]1-or [alpha]2-metanatrolite). Conversely, under high-[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] conditions ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] > ~1.3 mbar), dehydrated mesolite became amorphous (amorphous [T.sub.5][O.sub.10]) at 425[degrees]C. The local structure of amorphous [T.sub.5][O.sub.10] was characterized by PDF analyses, which showed the formation of twisted [T.sub.5][O.sub.10] nano-fibers [with dimensions (LWH) of ~6.9 x 6.9 x 6.3 [Angstrom]] resulting from breakage of the mesolite aluminosilicate framework. The two distinct high-temperature [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]-dependent phase transition paths illustrate the importance of considering the combined effects of temperature and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in mesolite. In addition, the low-temperature phase transition in mesolite, involving order-disorder of the extraframework cations, also showed a [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]-dependent transition temperature. Although, there is no path dependence on [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] for this transition, the local arrangement of Na, Ca, and vacancies in disordered metamesolite (formed through the extraframework cation order-disorder phase transition) likely influences the thermal stability of the aluminosilicate framework during further heating. Keywords: Phase transition, mesolite, XRD data, crystal structure DOI: 10.2138/am.2010.3443

Esperite from Franklin, New Jersey, was first described by Moore and Ribbe (1965) as monoclinic with a well-developed 'superlattice' a = 2 x 8.814(2) [Angstrom], b = 8.270(3)[Angstrom], c = 2 x 15.26(1)[Angstrom], [beta] [approximately equal to] 90[degrees], space group [P2.sub.1]/n (subcell), and the chemical formula Pb[Ca.sub.3][(ZnSi[O.sub.4]).sub.4]. They attributed 'superlattice' reflections to the ordered distributions of Pb and Ca cations over four beryllonite-type subcells for esperite with the Ca:Pb ratio greater than 2:1. We examined two esperite fragments from the type sample using single-crystal X-ray diffraction, electron microprobe analysis, and Raman spectroscopy. Although both fragments have Ca:Pb [approximately equal to] 1.8, one exhibits the 'superlattice' reflections as observed by Moore and Ribbe (1965), whereas the other does not. The sample without 'superlattice' reflections has unit-cell parameters a = 8.7889(2), b = 8.2685(2), c = 15.254(3) [Angstrom], [beta] = 90.050[(1).sup.o], V = 1108.49(4) [[Angstrom].sup.3], and the chemical composition [Pb.sup.1.00]([Ca.sup.1.86][Fe.sup.2+.sub.0.07][Mn.sub.0.04] [Cr.sup.3+.sub.0.02]).sub.[[summation] = 1.99] [([Zn.sub.1.00][Si.sub.1.00][O.sub.4]).sub.3]. Its crystal structure was solved in space group [P2.sub.1]/n ([R.sub.1] = 0.022). Esperite is isostructural with beryllonite, NaBeP[O.sub.4], and its ideal chemical formula should, therefore, be revised to Pb[Ca.sub.2][(ZnSi[O.sub.4]).sub.3], Z = 4. The Zn[O.sub.4] and Si[O.sub.4] tetrahedra in esperite share corners to form an ordered framework, with [Pb.sup.2+] occupying the nine-coordinated site in the large channels and [Ca.sup.2+] occupying the two distinct octahedral sites in the small channels. The so-called 'superlattice' reflections are attributed to triple twins, a trilling of ~60[degrees] rotational twinning around the b axis, similar to those observed in many other beryllonite-type materials. A phase transformation from a high-temperature polymorph to the esperite structure is proposed to be responsible for the twinning formation. Keywords: Esperite, beryllonite, Pb-Zn silicates, crystal chemistry, X-ray diffraction DOI: 10.2138/am.2010.3415

The crystal structure of gypsum-II, a polymorph of CaS[O.sub.4]*2[H.sub.2]O stable above 4 GPa, has been solved using single-crystal synchrotron X-ray diffraction data collected at 5.35 and 6.74 GPa. Gypsum-II is monoclinic, space group [P2.sub.1]/n, with lattice parameters a = 5.865(12), b = 15.045(14), c = 5.478(12) [Angstrom], [beta] = 115.3(2)[degrees], and V 437.0(14) [[Angstrom].sup.3] at 5.35 GPa, and a = 5.776(2), b = 15.017(2), c = 5.473(2) [Angstrom], [beta] = 114.98(4)[degrees], and V= 430.3(2) [[Angstrom].sup.3] at 6.74 GPa. The crystal structure has been refined to [R.sub.1] = 3.7 (5.35 GPa) and 3.9% (6.74 GPa). It closely resembles that of gypsum at room pressure with a stacking of Ca[O.sub.8] and S[O.sub.4] polyhedra along the b-axis to form layers. With increasing pressure, a continuous increase in distortion of the S[O.sub.4] tetrahedron and a strong change in the bonding style of the water molecules are observed. The mechanism of phase transformations previously hypothesized in gypsum, on the basis &high-pressure spectroscopic data, is here clarified for the polymorph stable between 4-8 GPa. Keywords: Gypsum, high pressure, crystal structure, phase transition, Ca-sulfate DOI: 10.2138/am.2010.3452

Anthoinite, AlW[O.sub.3][(OH).sub.3], from the Mt. Misobo Mine, Democratic Republic of the Congo, has triclinic symmetry with cell parameters a = 8.196(1)[Angstrom], b = 9.187(1) [Angstrom], c = 11.316(1) [Angstrom], [alpha] = 92.82(1)[degrees], [beta] = 94.08(1)[degrees], [gamma] = 90.23(1)[degrees], space group [bar.I1], Z = 8. The structure was solved by applying ab initio structure solution methods (Reverse Monte Carlo/Simulated Annealing) to both X-ray and neutron powder diffraction data and was refined using the Rietveld method. The structure is built up of two types of [M.sub.4][(O,OH).sub.16] planar tetrameric clusters of edge-sharing octahedra, one containing predominantly Al and the other predominantly W. The Al-rich and W-rich clusters interconnect via corner sharing to form stepped layers parallel to (001). The layers are held together by strong hydrogen bonding. The structure can be described as a rocksalt derivative structure, with the close-packed anion layers parallel to (012), and with Al and W atoms ordered into one third of the octahedral sites within the cubic close-packed anion lattice. The structure is complicated by partial disorder between Al and W in the tetrameric clusters and associated disorder in the H atom sites. Infrared and [sup.27]Al MAS NMR results are also presented for anthoinite. Keywords: Structure of anthoinite, ab initio structure determination, new layer structure in AlW[O.sub.3][(OH).sub.3], layer structure of anthoinite DOI: 10.2138/am.2010.3377

An As-rich variety of fergusonite-beta-(Y) occurs as greenish yellow pseudo-bipyramidal crystals up to 1 mm in length in centimeter-sized secondary cavities within sub-horizontal pegmatite dikes at Mount Cervandone (Western Alps, Italy). The mineral is associated with quartz, biotite, potassium feldspar, and orange-yellow barrel-shaped hexagonal crystals of synchysite-(Ce) up to 2 mm in length. Fergusonite-beta-(Y) crystallized during the Alpine metamorphism under amphibolite-facies conditions, as a result of interaction between As-enriched hydrothermal fluids, circulating through the pegmatite dikes, and precursor accessory minerals in the pegmatites enriched in high-field-strength elements. These pegmatites are of NYF (niobium-yttrium-fluorine) geochemical type and served as the principal source of Be, 5(, Nb, Ta, and rare-earth elements (REE) that were liberated and redeposited as rare Be-As-Y-REE minerals, including the As-rich fergusonite-beta-(Y). The latter mineral crystallizes with monoclinic symmetry [a - 5.1794(14), b = 11.089(3), c = 5.1176(14) [Angstrom], [beta] = 91.282(8)[degrees], V= 293.87(14) [[Angstrom].sup.3], space group 12/a] and has the empirical formula [([Y.sub.0.70][Dy.sub.0.07][Er.sub.0.05] [Ca.sub.0.05][Gd.sub.0.02][U.sub.0.02][Yb.sub.0.01] [Tb.sub.0.01][Th.sub.0.01][Nd.sub.0.01])[SIGMA]0.95] [([Nb.sub.o.68][As.sup.5+.sub.0.27][W.sub.0.06] [Ta.sub.0.01][Si.sub.0.01]).sub.[SIGMA]1.03][O.sub.4]. The crystal structure of fergusonite-beta-(Y) has been refined using a thermally untreated single crystal to [R.sub.1] = 6.6% for 441 observed reflections with [F.sub.o]/[sigma][F.sub.o] > 4. The incorporation of As in the structure of monoclinic fergusonite-type phases is discussed in the context of the data available for synthetic analogs. Keywords: Fergusonite, single crystal, X-ray diffraction, EMPA DOI: 10.2138/am.2010.3239

A new type of Al-rich hydroxylian pseudortuile (HPR), containing 64.6 wt% Ti[O.sub.2], 12.1 wt% [Al.sub.2][O.sub.3], 10.9 wt% [Fe.sub.2][O.sub.3], and 12.4 wt% [H.sub.2]O, has been identified in detrital heavy mineral concentrates from Central Kalimantan, Indonesia. The unusual translucent orange-colored grains have been characterized using electron microprobe analyses, thermal analyses, [sup.27]Al MAS NMR, and synchrotron XRD studies including the use of differential pair distribution function analysis, to determine how the Al is incorporated. The results support a model in which diaspore-form AIOOH is incorporated into nanopores in the solid hydrogel-like mineral. The HPR matrix structure comprises disordered unit-cell scale intergrowths of diaspore-type and rutile-type structure elements, which have a close dimensional match to the diaspore structure, thus providing a suitable template for epitactic nucleation and growth of the diaspore. The average composition of the grains is [Fe[Ti.sub.6][O.sub.10.8][(OH).sub.5.4]] x 1.8A1OOH x [H.sub.2]O, where the formula within the square brackets represents the HPR matrix, and the A1OOH and [H.sub.2]O occupy the intragrain pore volume. Keywords: Hydroxylian pseudorutile, Al-rich pseudorutile, synchrotron XRD study, diaspore-rutile intergrowth structure DOI: 10.2138/am.2010.3330

A sample of Mg-vermiculite from Santa Olalla (Spain) was studied by X-ray powder diffraction, electron microprobe, and thermo-gravimetry. The 3D structure is described as a disordered stack of two types of 2D building blocks, which are made up of one talc-type layer and one interlayer space containing hydrated [Mg.sup.2+] cations. We have succeeded in the refinement of both the atomic positions and occupancies of exchangeable cations and water molecules in the interlayer space of this vermiculite using the program package DIFFaX+. The position of the [Mg.sup.2+] cations is the only difference between the two layers. Besides the water molecules associated to the octahedrally coordinated [Mg.sup.2+], we also located water molecules in the interlayer space. The structural analysis confirms that vermiculite is a semi-ordered crystalline material characterized by the existence of a large density of defects due to random ~[+ or -]b/3 translations along the crystalline [010] direction. In this way, this structure can no longer be described by means of a unit cell repeated in 3D space. Instead, long-range order is only recognized in the a-b plane. The 3D structure is described by means of a recursive method. Keywords: Mg-vermiculite, stacking faults, X-ray diffraction, DIFFaX+ DOI: 10.2138/am.2010.3249

The crystal structure of a polycrystalline knorringite, [Mg.sub.3][([Cr.sub.0.8][Mg.sub.0.1][Si.sub.0.1]).sub.2][(Si[O.sub.4]).sub.3], synthesized at 11 GPa and T = 1500 [degrees]C in a multi-anvil press, has been refined from high-resolution synchrotron X-ray powder diffraction data. The structure is cubic, space group Ia[bar.3]d, a = 11.5935(1) [Angstrom], V = 1558.27(4) [[Angstrom].sup.3], [D.sub.calc] = 3.79 g/[cm.sup.3]. The structural formula indicates that knorringite is susceptible to majorite substitution at these synthesis conditions. The Cr-O distance, 1.959(7) [Angstrom], is similar to that in Cr-bearing pyrope [Mg.sub.3][Al.sub.2][(Si[O.sub.4]).sub.3]. This confirms that the magnitude of the Cr-O distance is not responsible for the difference in crystal field splitting values between green knorringite and red Cr-pyrope. A comparison with the structure of other Cr-garnet end-members shows that the Cr-O distance and the [sup.[4]]Si-O-Cr angle decrease with decreasing synthesis pressure and with increasing X-cation size. Keywords: Structure refinement, knorringite, XRD, synchrotron powder diffraction, Cr-garnet DOI: 10.2138/am.2010.3243

Anandite, a trioctahedral mica, has an ideal chemical formula of Ba[(FeMg).sub.3](Si[Fe.sup.3+])[O.sub.10](OH)S and a microprobe-derived formula of [([Ba.sub.0.96][K.sub.0.03] [Na.sub.0.01]).sub.[SIGMA]=1.00] [([Fe.sup.2+.sub.2.01][Mg.sub.0.46][Fe.sup.3+.sub.0.28][Al.sub.0.10] [Mn.sup.3+.sub.0.04][Mn.sup.2+.sub.0.04][Ti.sub.0.01].sub.[SIGMA]=2.93] [([Si.sub.2.60][Fe.sup.3+.sub.1.40]).sub.[SIGMA]=4.00][O.sub.10] [[(OH).sub.0.96][S.sub.0.84][Cl.sub.0.16][F.sub.0.04]].sub.[SIGMA]=2.00], where [S.sup.2-] primarily substitutes for [(OH).sup.-]. A single-crystal, X-ray structure determination of anandite-2M was refined to [R.sub.1] = 0.0443 and w[R.sub.2] = 0.1232 on [F.sup.2] in space group Am. Cell parameters are: a = 5.4431 (3), b = 9.4719(6), c = 20.042(1) [Angstrom], and [beta] = 95.046(1)[degrees]. Layer stacking is analogous to a 1M stacking pattern (parallel unidirectional a/3 shifts within layers and octahedral set I only occupied), however cation order and (S,OH) positional disorder produce a two-layer repeat with [beta] equaling ~95[degrees]. Subgroup symmetry of Am results from tetrahedral sheets within layers that are non-centrosymmetric with unequal compositions ([Si.sub.0.61][Fe.sup.3+.sub.0.39] vs. [Si.sub.0.79][Fe.sup.3+.sub.0.21]) and thicknesses (difference of 0.209 [Angstrom]), and there is positional and site-occupancy disorder (four sites with S of 0, 30, 52, and 58%) of (S,OH). Characteristics of anandite-2M, which are similar to those of anandite-20, include (1) alternation of smaller tetrahedral rings containing four Si-rich tetrahedra (T1a: 1.643 [Angstrom], T2b: 1.657 [Angstrom]) and two [Fe.sup.3+]-rich tetrahedra (T2a: 1.733 [Angstrom], T1b: 1.760 [Angstrom]) and larger rings containing four [Fe.sup.3+]-rich tetrahedra and two Si-rich tetrahedra within each layer; (2) nearly in-phase wave forms of basal O atoms across the interlayer ([DELTA]z = -0.110 and 0.011 [Angstrom] and across the interlayer [DELTA]z = -0.121 and 0.007 [Angstrom]); and (3) attraction that results in Ba being shifted toward S (0.070 [Angstrom]) and S being shifted toward Ba (0.117 [Angstrom] average) along the c axis, relative to the ideal. Bond-valence calculations show that Ba is shifted toward the undersaturated, bridging-basal O atoms of the [Fe.sup.3+]-rich tetrahedra and toward S-rich sites to achieve charge balance. Comparison of anandite-2M and anandite-20 shows that they possess unit cells (2M setting) that have nearly equal a axes, unequal b and c axes, and [beta] (anandite-2M is smaller by 0.0371 [Angstrom], larger by 0.08 [Angstrom], and smaller by 0.089[degrees], respectively). Moreover, anandite-20 exhibits larger [Fe.sup.3+]-rich tetrahedral rings than anandite-2M, which allow for a greater shift in Ba (difference of 0.03 [Angstrom]). The ordering and consequent absence of a twofold axis in anandite-2M allows the in-phase wave structure of basal O atoms, which was previously thought only possible in the orthorhombic P cell. Keywords: Anandite mica, single-crystal X-ray diffraction, two-layer monoclinic mica polytypes, phyllosilicate, Ba-rich mica, S-rich mica, Fe-rich mica

The crystal structure of the 2.5 hydrate MgSO4 phase was determined by simulated annealing from laboratory X-ray powder diffraction data measured from 2-140[degrees]2[theta] using CuK[alpha] radiation. The 2.5 hydrate is monoclinic, space group C2/c, with unit-cell parameters a - 18.8636(4) [Angstrom], b 12.3391(2) [Angstrom], c= 8.9957(2) [Angstrom], [beta] = 94.568(2)[degrees], V 2087.1(6) [[Angstrom].sup.3], and Z= 16. The model was refined using fundamental-parameters Rietveld refinement, converging to [R.sub.wp] = 8.89%, [R.sub.p] = 6.61%, [R.sub.exp] = 3.33%, [R.sub.Bragg] = 3.95%, and [chi square] = 2.67. The refined structure is consistent with a formula of 2.5 [H.sub.2]O. Bond-valence calculations for the refined model show that the structure is chemically sensible. In the refined structure, [[Mg(O,[H.sub.2]O).sub.6]] octahedra and [[SO.sub.4]] tetrahedra build up 2-D double-sheet slabs by sharing vertex O atoms, which are held together by inter-slab H-bonds involving [([SO.sub.4]).sup.2-] groups and [H.sub.2]O molecules coordinated with [Mg.sup.2+] cations to form the layer structure of the 2.5 hydrate phase. Keywords: Mg[SO.sub.4].2.5[H.sub.2]O, Mg[SO.sub.4].2.4[H.sub.2]O, crystal structure, simulated annealing, structure determination, powder diffraction, Rietveld refinement

Five clinopyroxenes containing various amounts of six-coordinated Si ([sup.VI]Si) in the Na([Mg.sub.0.5][Si.sub.0.5]) [Si.sub.2][O.sub.6] (NaPx)-NaAl[Si.sub.2][O.sub.6] (jadeite) system have been synthesized at 15 GPa and 1600[degrees]C and their structures studied with single-crystal X-ray diffraction and Raman spectroscopy. The results show that clinopyroxenes with [sup.V1]Si [less than or equal to] 0.33 atoms per formula unit (apfu) possess C2/c symmetry, whereas those with [sup.V1]Si [greater than or equal to] 0.45 apfu crystallize with P2/n symmetry. There is an obvious discontinuity in the unit-cell parameters a, [beta], and V as the [sup.V1]Si content increases from 0.33 to 0.45 apfu, suggesting that the C2/c-P2/n transition is first-order in character, rather than tricritical as reported for the transition from jadeite/diopside/augite to omphacite. The Mg and [sup.V1]Si cations in the P2/n structure are completely ordered into two nonequivalent octahedral sites, M1 and M1 (1), respectively, with M 1 being appreciably more distorted than M 1 (1). With increasing mean distance, the mean tetrahedral distance increases, whereas the O3-O3-O3 angle of the tetrahedral chain decreases systematically, consistent with the structural variation trends found in the jadeite-diopside system. A comparison of the Raman spectra reveals that the C2/c-P2/n transition is characterized by the splitting of many Raman bands in C2/c clinopyroxenes into doublets in P2/n, and such splitting becomes more pronounced with increasing [sup.V1]Si. For C2/c clinopyroxenes, all Raman bands become progressively broader with the increased substitution of([Si.sup.4+] + [Mg.sup.2+]) for [Al.sup.3+]. In addition, several new Raman bands, attributable to the presence of [sup.V1]Si, are observed. Together with previous data, we suggest that the maximum [sup.V1]Si content allowed for an Mg/Al dominated octahedral site is close to ~35%, above which [sup.V1]Si and Mg/ Al are likely to be ordered into distinct sites. Keywords: Clinopyroxenes, six-coordinated silicon, X-ray structure refinement, Raman spectroscopy, phase transformation

A synthetic pyroxene with composition LiFe[Ge.sub.2][O.sub.6] and space group P[2.sub.1]/c at ambient conditions was investigated by single-crystal X-ray diffraction using a diamond anvil cell. The unit-cell parameters and crystal structure were determined at eight different pressures up to 8.7 GPa. Between 4.16 and 4.83 GPa, the sample shows a strongly first-order phase transition as indicated by a drastic drop in a, c, [beta], and unit-cell volume. The transition is marked by the disappearance of b-type reflections (h + k = odd) forbidden in a C-centered lattice. The volume bulk modulus of the P[2.sub.1]/c phase is estimated to be 110 GPa as compared to 147 GPa of the C2/c one. The crystal structure evolution as a function of pressure is mainly influenced by the kinking of tetrahedral chains; the A and B non-symmetry equivalent chains of the P[2.sub.1]/c phase undergo strong deformations up to 4.16 GPa (A chain ~2%, B chain ~5.3%). At the transition, the two chains become symmetry equivalent and the single tetrahedral chain of the C2/c phase shows only minor deformations with pressure (~1.9%) due to its already strong kinking (~130 [degrees]). Such behavior is the main reason for the strong difference in compressibility between the low- and high-symmetry forms. Keywords: Single-crystal structure analysis, germanates, high-pressure phase transformations, X-ray diffraction

The crystal structure of sanderite, MgS[O.sub.4] x 2[H.sub.2]O, was determined from laboratory X-ray powder diffraction data measured from 2-140 [degrees]2[theta] using CuK[alpha] radiation. Sanderite is orthorhombic, space group P[2.sub.1][2.sub.1][2.sub.1], with unit-cell parameters a = 8.8932(1) [Angstrom], b = 8.4881(1) [Angstrom], c = 12.4401(2) [Angstrom], V = 939.16(3) [Angstrom], Z = 8. The crystal structure model was determined using the charge flipping method and was refined using fundamental parameters Rietveld refinement method to [R.sub.wp] = 6.52%, [R.sub.exp]: 1.89%, and [chi square] = 3.43. Bond-valence calculations for the refined model show that the structure is chemically reasonable. In the refined structure, [Mg.sup.2+] cations are coordinated by four O atoms from [[S[O.sub.4]].sup.2-] groups and by two [H.sub.2]O molecules, forming distorted octahedra. By sharing vertex O atoms, [S[O.sub.4]] tetrahedral and [Mg[O.sub.4]([[H.sub.2]O).sub.2]] octahedra build up a 3-D framework. Keywords: Sanderite, MgS[O.sub.4] x 2[H.sub.2]O, crystal structure, charge flipping, structure determination, powder diffraction

Aluminocerite-(Ce), ideally [(Ce,Ca).sub.9]Al[(Si[O.sub.4]).sub.3] [[Si[O.sub.3](OH)].sub.4][(OH).sub.3], is isostructural with cerite-(Ce) and cerite-(La). The holotype was found at the Ratti quarry, near Baveno, Italy, in millimeter-sized secondary cavities hosted in aplite-pegmatite veins and pods within pink granite. Aluminocerite-(Ce) forms aggregates of pseudo-octahedral to rhombohedral crystals flattened on the c axis. The cotype of aluminocerite-(Ce) was discovered at the Locatelly quarry, also near Baveno, where it occurs in centimeter-sized miarolitic cavities in pink granite. The mineral is pale pink to pink-reddish, with a white streak, and is translucent with a vitreous luster. Aluminocerite-(Ce) is non-fluorescent. The hardness based on the Mohs scale is 5, and the tenacity is brittle. Neither cleavage, fracture, or twinning were observed. Calculated density is 4.675 g/[cm.sup.3]. It is uniaxial, optically positive, with [n.sub.o] = 1.810-1.816 and [n.sub.e] = 1.812-1.822 ([lambda], = 589 nm) and non-pleochroic. The average of 15 electron microprobe analyses for the holotype gave (wt%): [Ce.sub.2][O.sub.3] 23.37; [Nd.sub.2][O.sub.3] 15.59; [La.sub.2][O.sub.3] 7.43; [Sm.sub.2][O.sub.3] 4.38; [Pr.sub.2][O.sub.3] 3.54; [Gd.sub.2][O.sub.3] 3.12; [Y.sub.2][O.sub.3] 1.68; [Dy.sub.2][O.sub.3] 0.46; [Yb.sub.2][O.sub.3] 0.07; CaO 8.31; [Fe.sub.2][O.sub.3] 0.47; [Al.sub.2][O.sub.3] 2.47; Si[O.sub.2] 24.01; and [H.sub.2]O 3.63 (calculated from crystal-chemical constraints), total 98.53 wt%, corresponding to the empirical formula [([Ca.sub.2.60][Ce.sub.2.49][Nd.sub.1.62][La.sub.0.80][Sm.sub.0.44] [Pr.sub.0.38][Gd.sub.0.30][Y.sub.0.26][Dy.sub.0.04][Yb.sub.0.01]).sub.[SIGMA] 8.94][([Al.sup.3+.sub.0.85][Fe.sup.3+.sub.0.10]).sub.[SIGMA]0.95] [(Si[O.sub.4]).sub.3][[Si[O.sub.3](OH)].sub.4] [(OH).sub.3.06], calculated on the basis of Si = 7. Aluminocerite-(Ce) is trigonal, space group R3c, with a =10.645(1), c = 38.019(5) [Angstrom], V = 3731 [[Angstrom].sup.3]. The strongest eight lines in the X-ray powder diffraction pattern are [d in [Angstrom] (I)(hkl)]: 3.405(27)(122), 3.250(26)(124), 2.914(100)(02,10), 2.647(58)(220), 2.198(40)(03,12), 1.923 (34) (238), 1.826(24)(051), and 1.732(46)(03,18). The crystal structure has been refined to R1 = 0.056 for 745 observed reflections. The name is an allusion to the fact that it is the Al-dominant analog of cerite-(Ce). Keywords: Aluminocerite-(Ce), single-crystal XRD, EMP analyses, new mineral, Raman spectroscopy

Molecular crystals of an [As.sub.4][S.sub.4-x][Se.sub.x] (0 [less than or equal to] x [less than or equal to] 4) solid solution were grown at 400[degrees]C using vacuum-sublimation and were characterized using single-crystal X-ray diffraction and electron microprobe analyses. The solid solution crystallizes in the monoclinic space group [P2.sub.1]/n with lattice parameters of a = 9.33-9.57 [Angstrom], b = 13.57-13.82 [Angstrom], c = 6.60-6.74 [Angstrom], [beta] = 106.4-106.7[degrees], V = 801-854 [[Angstrom].sup.3] and Z = 4. Substitution of Se for S in the [As.sub.4][X.sub.4] molecule causes nearly isotropic unit-cell expansion retaining identical molecular packing to the low-temperature form [alpha]-[As.sub.4][S.sub.4] (natural realgar). Crystal structure refinements show that Se is distributed with a strong preference for the X2 site. The As-X3 bond is slightly elongated in the solid-solution series. The bond length difference between As-X3 and the other As-X bonds increases with the Se content, thereby inducing atomic shift of the As4 bonds to X3 and X4 toward the side of X3. The atomic position of As4 returns to the place on the bisector between X3 and X4 at the [As.sub.4][Se.sub.4] end-member composition. Although As-As bonds shorten with Se content, the volume of the [As.sub.4][X.sub.4] molecule and the intercentroid distance between the nearest [As.sub.4][X.sub.4] molecules increase continuously, resulting in isotropic expansion of the unit cell in this solid-solution series. The strong site preference of Se for the X2 site suggests that S may be detached from that site more easily than from the remaining ones. On the contrary, very slight substitution of Se for S in the X3 site indicates that S in the X3 site is strongly bonded to two As atoms. Therefore, S is more stably incorporated into the X3 site than into the X2 site; these molecular features of the Se substitution in the [As.sub.4][X.sub.4] molecule are consistent with the proposed photoinduced transformation dynamics in realgar. Continuous illumination of the Se-containing realgar engenders alteration to pararealgar under identical transformation mechanisms to those of the realgar. Keywords: Realgar, [As.sub.4][S.sub.4], seleno-realgar, [As.sub.4] [Se.sub.4], solid solution, crystal structure

The crystal-structure, crystal-chemistry, and low-temperature behavior of a natural phillipsite-Na from the 'Newer Volcanic Suite,' Richmond, Melbourne district, Victoria, Australia [[[K.sub.0.75]([Na.sub.0.88][Ca.sub.0.57).sub.[SIGMA]1.45] [([Al.sub.2.96][Ti.sub.0.01][Si.sub.5.07).sub.[SIGMA]8.04][O.sub.16] x 6.2[H.sub.2]O (Z = 2) a = 9.9238(6), b = 14.3145(5), c = 8.7416(5) [Angstrom], [beta] = 124.920(9)[degrees], and V = 1018.20(9) [[Angstrom].sup.3], space group P[2.sub.1]/]m], have been investigated by means of in situ single-crystal X-ray diffraction, thermogravimetric analysis, and electron microprobe analysis in the wavelength dispersive mode. Two accurate structural refinements have been obtained on the basis of single- crystal X-ray diffraction data collected at 298 and 100 K, with: [R.sub.1] [(F).sub.298K] = 0.035, 3678 unique reflections with [F.sub.o] > 4[sigma]([F.sub.o]) and 195 parameters, and [R.sub.1] [(F).sub.298K] = 0.035, 3855 unique reflections, [F.sub.o] > 4[sigma]([F.sub.o]) and 195 parameters. In both refinements, the residuals in the final difference Fourier maps are Keywords: Zeolite, phillipsite, crystal chemistry, low temperature, single-crystal X-ray diffraction

The thermally induced structural modifications of the natural zeolite barrerite [[Na.sub.16] [Al.sub.16][Si.sub.56][O.sub.144] x 52[H.sub.2]O, a = 13.6239(4) [Angstrom], b = 18.2033(5) [Angstrom], c = 17.8317(7) [Angstrom], V = 4422.3(3) [[Angstrom].sup.3], space group Amma, framework type STI] were studied in a temperature-resolved X-ray powder diffraction experiment, using synchrotron radiation, in the temperature range 339-973 K. In the initial stage of heating, up to 508 K, barrerite Phase A (space group Amma) is stable, the unit-cell volume decreases by about 4% and a water release of about 66% is observed. Between 521 and 598 K, a phase transition to the collapsed so-caned barrerite Phase B (space group Amma) is observed. During the transition, the rotation of the [4.sup.2][5.sup.4] secondary building units causes a large decrease in cell volume and deformation of the channel system. Phase B, at 611 K, shows the statistical breaking of T-O-T bridges in the 4-rings and the migration of the involved tetrahedral atoms to new 'face-sharing' tetrahedra, with a consequent reduction of the free volume of the channels parallel to [100]. The new structure is stable up to 741 K and the total volume decrease is about 16%. A new phase appears from 754 K with cell parameters similar to those reported for the highly deformed barrerite Phase D and is stable up to 910 K, which is the temperature at which the total volume decrease is 22.5%. The material does not undergo amorphization up to the highest temperature investigated. Keywords: Zeolite, barrerite, dehydration, X-ray powder diffraction, synchrotron radiation, crystal structure

Here we report the first continuous time-resolved X-ray diffraction analysis of a biologically mediated mineral reaction. We incubated total membrane (TM) fractions of the facultative anaerobe Shewanella oneidensis in an anoxic environmental reaction cell with formate (as electron donor via formate dehydrogenase) and powdered bimessite, a layered [Mn.sup.3+,4+] oxide common to many soils. Using both synchrotron and conventional X-ray sources, we irradiated the reaction mixtures for up to two weeks and observed bioreduction and dissolution of birnessite and the concomitant precipitation of rhodochrosite [[Mn.sup.2+]C[O.sub.3]] and hausmannite [[Mn.sup.2+][Mn.sup.3+.sub.2]+[O.sub.4]]. The high time resolution of these experiments documented systematic changes in crystal structure during the breakdown of birnessite and the emergence of nanocarystalline rhodochrosite. In addition, the relative abundances of bimessite and rhodochrosite were quantified over time for different concentrations of TM fraction, allowing for the determination of rate equations that govern this bioreaction. Importantly, constant irradiation for two weeks did not stop the enzymatic reaction, suggesting that enzymes may be more resilient than whole cells when exposed to X-ray radiation. Keywords: Mn oxide, biological-mineral interactions, time-resolved XRD, birnessite, rhodochrosite, hausmannite

The crystal structure of a natural jadeite, NaAl[Si.sub.2][O.sub.6], was studied at room temperature over the pressure range 0-9.17 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at nine of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-Vdata yielded [V.sub.0] = 402.03(2) [[Angstrom].sup.3], K0 = 136.5(14) GPa, and [K.sup.'.sub.0] = 3.4(4). Jadeite exhibits strongly anisotropic compression with unit strain axial ratios of 1.00:1.63:2.10. Silicate chains become more O-rotated with pressure, reducing [angle]O3-O3-O3 from 174.7(1)[degrees] at ambient pressure to 169.2(6)[degrees] at 9.17 GPa and bringing the anions of jadeite closer to a cubic closest-packed arrangement. No evidence of a phase transition was observed over the studied pressure range. In an effort to understand pyroxene compressibilities, selected clinopyroxene bulk moduli were plotted against ambient unit-cell volumes. Two trends were identified and are explained in terms of differences in M2-O3 bonding topologies and the geometric relationship of the bonds with tetrahedral rotation in the silicate chains. Bonds positioned to favor the tetrahedral rotation upon compression are termed 'sympathetic,' whereas bonds positioned to resist the rotation are termed 'antipathetic.' Examination of the different pyroxene structures indicates that structures containing antipathetic M2-O3 bonds are less compressible than those with only sympathetic M2-O3 bonds. This behavior has not been previously recognized. Keywords: Jadeite, crystal structure, high pressure, single-crystal X-ray diffraction, pyroxene, clinopyroxene, compressibility, elasticity, bulk modulus

The determination of an accurate crystal structure for the title zirconium complex as well as a complete electron density (ED) analysis is studied by the high-resolution synchrotron X-ray diffraction. The ED distribution and its topological analysis give new insight into the electronic structure of the title zirconium complex.