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The dehydration-rehydration process in gmelinite-Na [absolute value of [Na.sub.7.27] [K.sub.0.28] [Ca.sub.0.15] [([H.sub.2]O).sub.21.85]][[Al.sub.7.71][Si.sub.17.24][O.sub.48]]-GME, a natural zeolite that can be described as a parallel stacking of double six rings of tetrahedra in the AABB sequence, was studied by X-ray diffraction data. Its space group is [P6.sub.3]/mmc with a = 13.764(1) and c = 10.078(1) [Angstrom] cell parameters. Single-crystal data collections were performed at room conditions and at increasing temperatures, in a hot nitrogen stream, up to the fragmentation of the crystals, which occurs at a temperature as low as 100[degrees]C, and afterward the crystal was cooled down to room conditions. X-ray powder diffraction data showed that gmelinite-Na transforms into a new structure with an AFI-type topology at about 300[degrees]C. At room conditions, extraframework cations are located in two symmetrically independent positions, both of which are coordinated to either framework O atoms or water molecules. When the mineral is heated to 90 [degrees]C, about 40% of [H.sub.2]O is lost, and one cation site splits over two positions, which are three-coordinated to the framework O atoms. The dehydration process is completely reversible over a period of hours. X-ray single-crystal data has highlighted that gmelinite-Na when quenched at 100 K displays remarkable modifications in its extraframework content, resulting in a strong disorder in its extraframework ions. As in the case of heating, the mineral restores its structural features when brought back to room temperature. Keywords: Gmelinite, dehydration, rehydration, in situ crystal structure, low temperature DOI: 10.2138/am.2010.3419

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 present paper reports a crystal-chemical study of minerals belonging to the proustite--pyrargyrite group by evaluating 32 natural samples of proustite and 27 samples of pyrargyrite from different localities that have variable chemical compositions. The unit-cell parameters were modeled as a function of the Sb contents. The a parameter is strongly influenced by the As [left and right arrow] Sb substitution, whereas the influence on the c parameter is very minor (nearly constant trend). The following equations were obtained from the linear fitting of the data: [a.sub.pred] = 10.8433(3) + 0.2019(4)Sb (apfu) [C.sub.pred] = 8.7189(6) + 0.0059(9)Sb (apfu) [V.sub.pred] = 887.77(7) + 34.0(1)Sb (apfu). The crystal structure of the members of the proustite--pyrargyrite solid solution consists of two sets of spiral chains parallel to the c-axis. Each chain contains alternating Ag and S atoms, with each chain being connected by As and Sb atoms, which are the apices of flat pyramidal As[S.sub.3]/Sb[S.sub.3] groups. Each S atom is part of a different Ag-S chain. The compositional data support the concept that proustite--pyrargyrite solid solutions re-equilibrate and exsolve to near end-member upon cooling. Examples of intermediate compositions are rare in nature and must have quenched above the solvus. Keywords: Sulfosalts, electron microprobe, proustite, pyrargyrite DOI: 10.2138/am.2010.3563

Since its first discovery in nature, natrolite has been largely known as a sodium aluminosilicate zeolite, showing very limited preference toward cation exchange. Here we show that fully K-exchanged natrolite can be prepared from natural Na-natrolite under mild aqueous conditions and used to subsequently produce Rb-and Cs-exchanged natrolites. These cation-exchanged natrolites exhibit successive volume expansions by ca. 10, 15.7, and 18.5% for K-, Rb-, and Cs-forms, respectively, compared to the original Na-natrolite. This constitutes the largest, ever-reported volume expansion via cation substitution observed in zeolites and occurs by converting the elliptical channels into progressively circular ones. The observed cation-dependent changes in the channel volume and shape thus show the flexibility limits of the natrolite framework and suggest the possible existence of compositionally altered analogues in suitable environments as well as a novel means to tailor the cation selectivity of this class of small pore zeolites toward various industrial and environmental applications. Keywords: Natrolite, ion-exchange, volume expansion, Rietveld refinement DOI: 10.2138/am.2010.3607

The crystal structures of biogenic Mn oxides produced by three fungal strains isolated from stream pebbles were determined using chemical analyses, XANES and EXAFS spectroscopy, and powder X-ray diffraction. The fungi-mediated oxidation of aqueous [Mn.Sup.2+] produces layered Mn oxides analogous to vernadite, a natural nanostructured and turbostratic variety of birnessite. The crystallites have domain dimensions of ~10 nm in the layer plane (equivalent to ~35 Mn[O.sub.6] octahedra), and ~1.5-2.2 nm perpendicularly (equivalent to ~2-3 layers), on average. The layers have hexagonal symmetry and from 22 to 30% vacant octahedral sites. This proportion likely includes edge sites, given the extremely small lateral size of the layers. The layer charge deficit, resulting from the missing layer [Mn.sup.4+] cations, is balanced mainly by interlayer [Mn.sup.3+] cations in triple-corner sharing position above and/or below vacant layer octahedra. The high surface area, defective crystal structure, and mixed Mn valence confer to these bio-minerals an extremely high chemical reactivity. They serve in the environment as sorption substrate for trace elements and possess catalytic redox properties. Keywords: Manganese oxide, birnessite, biominerals, phyllomanganate, crystal structure DOI: 10.2138/am.2010.3516

Forsterite ([Mg.sub.2]Si[O.sub.4]) is a silicate mineral frequently studied in the Earth sciences as it has a simple crystal structure and fast dissolution kinetics (elemental release rates under typical conditions on the order of [l0.sup.-7] mol/[m.sup.2]/[s.sup.1]). During the dissolution process, spectroscopic techniques are often utilized to augment solution chemical analysis and to provide data for determining reaction mechanisms. Nuclear magnetic resonance (NMR) is able to interrogate the local bonding arrangement and coordination of a particular nuclide to obtain structural information. Although previous NMR studies have focused on the silicon and oxygen environments in forsterite, studies focusing on the two nonequivalent magnesium environments in forsterite are limited to a few single-crystal studies. In this study, we present the results of [sup.25]Mg MAS, MQMAS, and static QCPMG experiments performed on a powdered sample of a pure synthetic forsterite. We also present spectral fits obtained from simulation software packages, which directly provide quadrupolar parameters for [sup.25]Mg nuclei occupying each of the two nonequivalent magnesium sites in the forsterite structure. These results are compared to calculations of the electric field gradient tensor conducted in previous ab initio studies to make definitive assignments correlating each peak to their respective magnesium site in the forsterite structure. Althought previous NMR investigations of forsterite have focused on single-crystal samples, we have focused on powdered forsterite as the increased surface area of powdered samples makes them more amenable to laboratory-scale dissolution studies and, ultimately, the products from chemical weathering may be monitored and quantified. Keywords: Forsterite, magnesium, [sup.25]Mg, NMR, MQMAS, QCPMG DOI: 10.2138/am.2010.3403

Ottoite, [Pb.sub.2]Te[O.sub.5], is a new tellurate from Otto Mountain near Baker, California. Most of the mining on Otto Mountain occurred between 1940 and 1970 and is attributed to Otto Fuetterer, for whom the mountain is now named. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins, which intersect granitic rocks. Ottoite is directly associated with acanthite, bromine-rich chlorargyrite, gold, iodargyrite, khinite, wulfenite, and four other new tellurates: housleyite, mark-cooperite, thorneite, and timroseite. Various other secondary minerals occur in the veins, including two other new secondary tellurium minerals, paratimroseite and telluroperite. Ottoite and most other secondary minerals of the quartz veins are interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of the veins. A later generation of quartz mineralization then recemented the breccias, effectively isolating and protecting the secondary mineralization from further alteration. Ottoite is monoclinic, space group 12/a, with the unit cell: a = 7.5353(6), b = 5.7142(5), c = 10.8981(12) [Angstrom], [beta] = 91.330(6)[degrees], V= 469.13(8) [[Angstrom].sup.3] , and Z = 4. The mineral occurs as complex spear-shaped crystals in subparallel to divergent intergrowths. It is yellow and transparent to translucent, with a pale yellow streak and adamantine luster. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture and two cleavages in the [100] zone at -90[degrees]--possibly on {010} and {001}. The calculated density is 8.721 g/[cm.sup.3]. Ottoite is biaxial (-), with a large 2 V, but indices of refraction are too high to be measured. The optic orientation could only partially be determined: Y [approximately equal to] a. No pleochroism was observed. Electron microprobe analyses provided the following averages: PbO 68.88 and Te[O.sub.3]28.03, total 96.95 wt%; the empirical formula (based on O = 5) is [Pb.sub.1.96][Te.sup.6+.sub.1.01][O.sub.5]. The strongest powder X-ray diffraction lines are [[d.sub.obs] in [Angstrom] (hkl) I]: 3.131 ([bar.2]02) 64, 3.055 (013) 90, 3.015 (211) 100, 2.112 (522) 29, 1.810 (006, 215) 21, 1.773 (411,402) 43, 1.686 (033, 231) 20. The crystal structure (R~ = 0.020) consists of straight chains of trans-comer-sharing [Te.sup.6+][O.sub.6] octahedra parallel to a, which are joined by bonds to Pb atoms. The Pb atom exhibit markedly lopsided 11-coordination, typical of Pb2+ with stereoactive 6s2 lone-pair electrons. The powder X-ray diffraction pattern of ottoite is very similar to that reported for girdite. Examination of girdite type material suggests that its description was based upon data obtained from at least two and possibly three different phases, one of which may correspond to ottoite. Keywords: Ottoite, girdite, new mineral, tellurate, crystal structure, stereoactive lone-pair, Otto Mountain, California DOI: 10.2138/am.2010.3510

Housleyite, [Pb.sub.6]Cu[Te.sub.4][O.sub.18][(OH).sub.2], is a new tellurate from Otto Mountain near Baker, California, named in honor of Robert M. Housley. The new mineral occurs on fracture surfaces and in small vugs in brecciated quartz veins. Housleyite is directly associated with acanthite, cerussite, gold, iodargyrite, khinite-40, wulfenite, and three other new tellurates: markcooperite, ottoite, and thorneite. A variety of other secondary minerals occur in the veins, including three other new secondary tellurium minerals, paratimroseite, telluroperite, and timroseite. Housleyite is monoclinic, space group [P2.sub.1]/n, a = 7.8552(5), b = 10.4836(7), c = 11.0426(8) [Angstrom], [beta] = 95.547(2)[degrees], and Z = 2. Crystals are prismatic to bladed with elongation parallel to b and typically occur in bow tie-like aggregates, drusy balls, and irregular sprays. It is pale to medium greenish blue and transparent, with pale blue streak and adamantine luster. Mohs hardness is estimated at 3. The mineral is brittle, with an irregular fracture. Cleavage was not observed, but is likely on { 101}. The calculated density is 7.845(1 ) g/[cm.sup.3]. Housleyite is biaxial (+), with 2V= 50[degrees] to 60[degrees] and strong inclined dispersion, r > v, but indices of refraction are too high to be measured. The optic orientation is Y = b, Z and c [approximately equal to] 40[degrees] in obtuse [beta] and pleochroism is Y (medium green-blue) > Z (light green-blue) > X. Energy dispersive spectroscopy provided PbO 62.53, CuO 3.77, Te[O.sub.3] 32.85, [H.sub.2]O 0.84 (structure), total 99.99 wt%.; the empirical formula (based on O = 20) is [Pb.sub.5.99][Cu.sub.1.01][Te.sub.4.00][O.sub.18][(OH).sub.2]. The strongest powder X-ray diffraction lines are [[d.sub.obs] in [Angstrom] (hkl) I]: 3.336 ([bar.2]02, 031,122) 69, 3.292 ([bar.1]13) 50, 3.195 (130, 103) 100, 3.068 ([bar.2]21,202) 47, 3.007 (023) 49, 2.942 (032, 212) 80, 2.723 (123,[bar.2]13, 132) 29, 2.580 (230, [bar.3]01, [bar.2]31) 38. The crystal structure ([R.sub.1] = 0.028) consists of comer-sharing chains of Te[O.sub.6] octahedra along [101] linked into slabs parallel to {10[bar.1]} by sharing edges and comers with strongly Jahn-Teller (4+2) distorted and severely skewed CuO6 octahedra. Lead (Pb) atoms in lopsided nine- and elevenfold coordinations form additional links within and between the octahedral sheets. Keywords: Housleyite, new mineral, tellurate, crystal structure, Otto Mountain, California DOI: 10.2138/am.2010.3511

A new high-pressure form of topaz-OH (denoted here topaz-OH 11) was obtained at 14 GPa and 1400[degrees]C. The X-ray diffraction pattern of this phase can be indexed by an orthorhombic cell with a = 4.72318(5), b = 8.91480(9), and c = 2.77276(3) [Angstrom]. The lengths of a and b are similar, but c is approximately a third of that for a previously reported topaz-OH (denoted topaz-OH I). The structural formula of topaz-OH II can be written as ([Al.sub.0.68][Si.sub.0.32])[([O.sub.0.66][(OH).sub.0.34]).sub.2], suggesting significant cation disorder in the structure. The crystal structure of topaz-OH II is solved using powder synchrotron X-ray diffraction data, and refined with constraints provided by a separate multi-nuclear NMR study. The structure has similarities with topaz-OH I and diaspore ([alpha]-A1OOH) structures, having partially occupied double edge-shared octahedral chains, and 2 x 1 tunnels with partially occupied tetrahedral and octahedral sites. Keywords: Crystal structure, high-pressure studies, phase transition, order-disorder DOI: 10.2138/am.2010.3555

Schwertmannite is a poorly crystalline mineral that forms ochre rusts and precipitates in acid mine environments. Despite its ubiquity and its role as scavenger of important contaminants such as arsenic or selenium, its structure has not been yet determined. Here, a structure for schwertmannite is presented based on pair distribution function (PDF) data, X-ray diffraction (XRD) analyses, and density functional theory (DFT) calculations. We propose a structure formed by a deformed frame of iron octahedra similar to that of akaganeite. Simulations of X-ray diffraction patterns unveil the presence of long-range order associated with the position of the sulfate molecules, providing a useful way to discern two types of sulfate complexes in the structure. The simulations suggest that two sulfate molecules per unit cell are present in the structure forming one outer sphere and one inner sphere complex inside the channels formed by iron octahedra. Knowledge of the positions of the sulfates in the structure will help to better understand exchange processes with oxyanions of trace contaminants, such as arsenate, chromate, or selenate, that strongly influence their biogeochemical cycling in mining ecosystems. Keywords: Schwertmannite, diffraction, structure, X-ray, pair distribution function, DFT, iron, sulfate DOI: 10.2138/am.2010.3446

A new polymorph of topaz-OH (denoted as topaz-OH II) was recently discovered at higher P-T conditions than has been known thus far (denoted as topaz-OH I). High-resolution [sup.1]H, [sup.29]Si, and [sup.27]Al nuclear magnetic resonance (NMR) and micro-Raman spectroscopy are applied to shed light on the crystal chemistry of both polymorphs. Topaz-OH I, synthesized at 7 GPa and 640 [degrees]C, is stoichiometric (Si/Al = 0.5) with a largely ordered local structure. Higher P-T topaz-OH I synthesized at conditions close to the polymorphic phase transition boundary, on the other hand, shows lower Si/A1 ratios (0.44-0.45) and greater local structural disorder [including a small fraction (-3%) of octahedral Si with a unique [sup.29]Si chemical shift near-133 ppm]. The latter may be accounted for by the development of defects (Si/Al in normally vacant octahedral sites and vacancies in the tetrahedral sites) at higher P-T conditions. Topaz-OH II synthesized at 13.5~14 GPa and 1300-1400 [degrees]C similarly exhibits low Si/Al ratios (0.41-0.46). The NMR and Raman spectra for these topaz-OH II are, in general, broader and revealed a substantial fraction (33-37%) of octahedral Si with a range of [sup.29]Si chemical shifts (-130 to -190 ppm), a small fraction (2-3%) of tetrahedral Al, and a range of (and overall shorter) hydrogen-bonding distances than topaz-OH I. Therefore, the phase transition from topaz-OH I to II is characterized by both a significant increase in the occupied octahedral/tetrahedral site ratio as well as disordering of cation distribution, which is unique from the viewpoint of crystal chemistry. Keywords: NMR spectroscopy, Raman spectroscopy, high pressure, crystal structure, phase transition, vacancy, vacant site, Al-Si disorder, hydrogen bonding DOI: 10.2138/am.2010.3471

[Fe.sup.3+] and [Mn.sup.3+] distributions on octahedral M1, M2, and M3 sites in synthetic epidote/piemontite from [Ca.sub.2][Al.sub.2][Fe.sup.3+.sub.l-q][Si.sub.3][O.sub.12.5] starting material and their effects on the crystal structure were investigated using X-ray Rietveld and [sup.57]Fe Mossbauer methods. Epidote and piemontite were crystallized as almost single phases from q = 1.0, 0.75, 0.5, and 0.25 starting materials at [P.sub.fluid] of 200-400 MPa and a temperature of 500[degrees]C, using standard cold-seal pressure vessels. The [Mn.sub.2][O.sub.3]-Mn[O.sub.2] buffer was used to produce fog adequate to maintain [Fe.sup.3+] and [Mn.sup.3+]. The Rietveld refinements converged to goodness-of-fit ranges from 1.21 to 1.60. At this temperature, site preferences of [summation]([Fe.sup.3+] + [Mn.sup.3+]) for octahedral sites are M3>MI(>>M2). [K.sub.D] values of [summation]([Fe.sup.3+] + [Mn.sup.3+]), where [K.sub.D] = [([Fe.sup.3+] + [[Mn.sup.3+] )/Al].sup.M1] /[([Fe.sup.3+] + [[Mn.sup.3+])/Al].sup.M3], (0.05-0.13) are similar to those of individual [Mn.sup.3+] and [Fe.sup.3+] vs. [Al.sup.3+], respectively. However, the [K.sub.D] values of [Fe.sup.3+] and [Mn.sub.3+] for M1 and M3, where [K.sub.D] = [([Fe.sup.3+]/[Mn.sup.3+]).sup.M1]/ [([Fe.sup.3+]/[Mn.sup.3+]).sup.M3], vary with [Fe.sup.3+.sub.Total]: [Mn.sup.3+.sub.Total] ratios. In epidote with [Fe.sup.3+] content larger than 0.4 atoms per formula unit (apfu) and [Mn.sup.3+] < 0.6 apfu, [Fe.sup.3+] has a stronger preference for M1 than [Mn.sup.3+]. In piemontite with 0.12 [Fe.sup.3+] and 0.73-0.78 [Mn.sup.3+] apfu, the preference of [Mn.sup.3+] for M1 is greater than that of [Fe.sup.3+]. The site occupancies of individual [Mn.sup.3+] and [Fe.sup.3+] are governed by the individual [K.sub.D] values and the [Mn.sup.3+] and [Fe.sup.3+] concentrations in corresponding epidote and piemontite. Variations of the unit-cell parameters indicate the combined result of linear variation due to Al [left and right arrow] [Fe.sup.3+] substitution and nonlinear variation due to Al [left and right arrow] [Mn.sup.3+] substitution. Keywords: Epidote, piemontite, synthesis, Rietveld refinement, M6ssbauer spectroscopy DOI: 10.2138/am.2010.3418

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

This paper reports the results of an in situ high-pressure synchrotron X-ray powder diffraction investigation on the natural zeolite boggsite [([K.sub.0.06][Na.sub.0.36][Sr.sub.0.01] [Ca.sub.7.00] [Mg.sub.1.20])([Al.sub.17.52][Si.sub.78.62][Fe.sub.0.05][O.sub.192]) x 82.3 [H.sub.2]O]. The study was performed using both a (16:3:1) methanol:ethanol:water mixture (m.e.w.) as a nominally 'penetrating' hydrostatic P-transmitting medium and silicon oil (s.o.) as a'non-penetrating' medium. The studied pressure ranges are: [P.sub.amb] -7.6 and [P.sub.amb] -5.9 GPa in m.e.w and s.o., respectively. No complete X-ray amorphization is observed up to the highest investigated pressures, and the original unit-cell parameters are almost completely recovered upon decompression in both media. The reductions of a, b, c, and V, within the pressure-ranges investigated, are 5.3, 4.2, 4.0, and 13.0% in s.o. and 4.1, 4.1, 3.8, and 11.5% in m.e.w. The Rietveld structural refinements of the powder patterns of the experiments in m.e.w, converged successfully up to 3.6 GPa and demonstrated the penetration of 13 additional water molecules between 0.3 and 2.9 GPa. This over-hydration occurs without any unit-cell volume expansion and can be explained by the fact that no new extraframework sites arise during compression and that water penetration is the only factor to increase the occupancy of already existing sites. Boggsite compressibility is higher in s.o. than in m.e.w. In particular, compressibility in m.e.w. is lower below 3 GPa, whereas above this pressure, the P-V trend becomes similar in the two media. This can be ascribed to the fact that, during water molecule penetration (0.3 < P < 3 GPa), the effect of the P-transmitting medium is directed to compress the system as well as to penetrate the channels. Keywords: Zeolite, boggsite, high pressure, compressibility, over-hydration, crystal structure, synchrotron XRPD data DOI: 10.2138/am.2010.3482

The V K-edge spectrum of a V-bearing grossular garnet (tsavorite) single crystal has been measured by high-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS). First-principles calculations based on the density functional theory (DFT) reproduce the experimental spectra well, including the angular dependence of the pre-edge. The latter arises from pure electric quadrupole transitions since vanadium is incorporated in a centrosymmetric site, which inhibits the electric dipole transitions. An interpretation of the spectral features is given using a monoelectronic description of the transitions involved in the X-ray absorption process. The assignment of experimental pre-edge peaks in terms of 1s-3d transitions makes it possible to determine the magnitude of the 3d-splitting, which is similar to the 10 Dq crystal-field value determined from optical absorption spectroscopy. DFT calculations also indicate a full structural relaxation around [V.sup.3+] substituting [Al.sup.3+] in the garnet structure. The angular dependence only causes weak variations of the pre-edge intensity, which supports the use of V-bearing grossular garnet as a reference compound for octahedral [V.sup.3+]. Keywords: Vanadium, garnet, HERFD-XAS, DFT calculations, K pre-edge, angular dependence, structural relaxation, crystal-field splitting DOI: 10.2138/am.2010.3432

Akaogiite, an ultra-dense polymorph of Ti[O.sub.2] was encountered in heavily shocked garnet-cordieritesillimanite gneiss in the Suevite breccia of the Ries meteorite impact crater in Germany. The chemical formula ofakaogiite is Ti[O.sub.2], containing (wt%) Ti[O.sub.2] 97.6-97.7; [Nb.sub.2][O.sub.5] 0.15-0.20, and FeO 0.11-0.14. The empirical formula is: [Ti.sub.0.998][Fe.sub.0.002][Nb.sub.0.001][O.sub.2]. Akaogiite is optically distinguishable from futile only in reflected light microscopy, through its slightly higher brightness and the intense royal blue color of its internal reflections in crossed nicols. The mineral grains consist of countless randomly oriented submicrometer particles. In situ micro-beam X-ray diffraction established akaogiite to be monoclinic with the baddeleyite-type structure. Cell parameters are a = 4.606(2) [Angstrom], b = 4.896(3) [Angstrom], c = 4.933(3) [Angstrom], and [beta] = 99.17[(6).sup.o]; space group [P2.sub.1]c; molar volume = 16.82(2) cmTmol; density = 4.72 g/[cm.sup.3]. Akaogiite coexists in the shocked gneiss with graphite-diamond phase transition assemblage, a second dense Ti[O.sub.2] polymorph with the scrutinyite-type structure (Ti[O.sub.2]-11), liquidus idiomorphic jadeite inclusions in melt pockets in garnet, and a new FeTi[O.sub.3]-polymorph with the Li-niobate structure. The high-pressure assemblage constrains the equilibrium peak-shock pressure to be [less than or equal to] 22 GPa and a post-shock temperature Keywords: Akaogiite, Ries Crater, suevite impact breccia, shock, rutile, Ti[O.sub.2]-11, graphite, diamond, Li-niobate structured FeTi[O.sub.3] DOI: 10.2138/am.2010.3425

Kapundaite, ideally [(Na,Ca).sub.2][Fe.sup.3+.sub.4][(P[O.sub.4]).sub.4] [(OH).sub.3] x 5[H.sub.2]O, is a new mineral (IMA2009-047) from Toms phosphate quarry, Kapunda, South Australia, Australia. The new mineral occurs as cavernous aggregates of fibers up to several centimeters across, associated with leucophosphite, natrodufrenite, and meurigite-Na crystals and amorphous brown, black, and/or greenish coatings. Individual kapundaite crystals are very thin flattened fibers up to a few millimeters in length, but typically no more than a few micrometers in thickness. The main form observed is {100}; other forms in the [010] zone are present, but cannot be measured. Crystals of kapundaite are pale to golden yellow, transparent to translucent, have a yellow streak and silky luster, and are non-fluorescent. Mohs hardness is estimated to be about 3; no twinning or cleavage was observed. Kapundaite is biaxial (+), with indices of refraction [alpha] = 1.717(3), [beta] = 1.737(3), and [gamma] = 1.790(3). 2V could not be measured; [2V.sub.cale] is 64.7[degrees]. The optical orientation is Z = b, Y [approximately equal to] c with weak pleochroism: X= nearly colorless, Y= light brown, Z = pale brown; absorption: Y> Z > X. No dispersion was observed. The empirical chemical formula (mean of seven electron microprobe analyses) calculated on the basis of 24 O is ([Ca.sub.1.13][Na.sub.0.95])[summation]2.08[([Fe.sup.3+.sub.3.83] [Mn.sub.0.03][Al.sub.0.02][Mg.sub.0.01]).sub.[summation]3.89] [P.sub.3.92][O.sub.16]([OH).sub.3] x 5[H.sub.2.11]O. Kapundaite is triclinic, space group P[bar.1], a = 6.317(5), b - 7.698(6), c = 9.768(7) [Angstrom], [alpha] = 105.53[(1).sup.o], [beta] = 99.24[(2).sup.o], [gamma] = 90.09[(2).sub.o], V = 451.2(6) [[Angstrom].sup.3], and Z- 1. The five strongest lines in the powder X-ray diffraction pattern are [[d.sub.obs] in [Angstrom], (I) (hkl)]: 9.338 (100) (001 ), 2.753 (64) (2[bar.1]1), 5.173 (52) (011 ), 2.417 (48) ([bar.2][bar.1]-3, 202, 0[bar.1]4), and 3.828 (45)(0[bar.2]1). The crystal structure was solved from single-crystal X-ray diffraction data using synchrotron radiation and refined to [R.sub.1] = 0.1382 on the basis of 816 unique reflections with [F.sub.o] > 4[sigma]F. The structure of kapundaite is based on a unique corrugated octahedral-tetrahedral sheet, which is composed of two types of chains parallel to a. Kapundaite is structurally related to melonjosephite. The mineral is named for the nearest town to the quarry. Keywords: Kapundaite, new mineral, phosphate, Toms phosphate quarry, crystal structure, octahedral-tetrahedral sheet, melonjosephite DOI: 10.2138/am.2010.3466

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

Coulsellite, Ca[Na.sub.3]Al[Mg.sub.3][F.sub.14], from the Cleveland tin mine at Luina, western Tasmania, has a rhombohedral distortion of the cubic pyrochlore [A.sub.2][B.sub.2][X.sub.6]Y structure, with a = 7.1756(1) [Angstrom], [alpha] = 59.867[(1).sup.o], space group R[bar.3]m, Z = 1. The corresponding hexagonal cell parameters are a = 7.1620(1) [Angstrom], c = 17.5972(3) [Angstrom]. The crystals are multiply twinned about threefold axes of the pseudocubic cell. The structure was determined using X-ray data collected on a twinned crystal and refined to Robs = 0.027 for 452 observed reflections with 1 > 2[sigma](I). The structure is possibly unique among published structures of pyrochlore-like minerals in having full 1:3 ordering of Ca:Na in the A sites and Al:Mg in the B sites. Transmission electron photomicrographs show a nanodomain structure due to twinning on a scale of ~5 nm. Keywords: Rhombohedral pyrochlore, new fluoride mineral, structure determination, 1:3 cation ordering in Ca[Na.sub.3]Al[Mg.sub.3][F.sub.14] DOI: 10.2138/am.2010.3360

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

In this paper, I demonstrate that the complex structure observed in natural dendritic zircon, which crystallized from a mafic magma, can be approximated by a simple model of deterministic volume-filling fractal growth. The model comprises a novel dendritic growth process that reveals a previously unrecognized underlying structure to complex dendritic crystals, and provides an ideal way of maximizing surface area at the crystal-melt interlace during dendritic crystal growth. This addresses the important kinetic effect of creating interfacial area. In turn, this relates to dissipation of the latent heat of fusion from the moving crystal-melt interlace, which, in addition to chemical diffusion, is known to be a fundamental rate-controlling process in dendritic crystal growth. A new mechanism of tip-splitting branch formation in dendritic crystals is proposed. Although both types of branch formation seem to occur simultaneously, the newly proposed mechanism operates at larger length scales and independently of classical side-branching linked with periodic perturbations caused by thermal noise. It is shown that this type of modeling potentially has applications in metallurgical engineering; and in predicting the relative lengths, orientations, and spacings of branches in mathematical modeling studies of natural and experimentally grown dendritic crystals. Keywords: Dendrite, zircon, fractal, alloy casting, crystal growth DOI: 10.2138/am.2010.3320

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

This paper reports a complete set of TG, DTG, and DTA data, coupled with emitted gas analysis, for well-constrained, almost pure serpentine samples. Serpentine dehydroxylation takes place between 550 and 800 [degrees]C, with DTG and DTA peak temperatures progressively decreasing from antigorite (720 and 715 [degrees]C, respectively) to lizardite (708 and 714 [degrees]C), polygonal serpentine (685 and 691 [degrees]C), and chrysotile (650 and 654 [degrees]C). Antigorite has an additional diagnostic signal at ~740-760 [degrees]C, always absent in the other serpentines, and dependent on antigorite superperiodicity (T shift of ~20 [degrees]C from 36 to 49 [Angstrom] modulation wavelength). A sharp exothermic peak occurs at extremely constant temperatures (~820 [degrees]C), independently from the starting serpentine structure. The high-T mineral assemblage is always represented by forsterite and enstatite. Based on the observed relationships between serpentine structures and DTG/DTA dehydroxylation temperatures, thermal analysis may represent a useful tool for serpentine identification, particularly in the case of natural massive samples where different varieties are mutually intermixed. The accurate definition of serpentine mineralogy would have obvious implications in both geological-petrological and health-related issues. Keywords: Serpentine, lizardite, antigorite, dehydroxylation, thermal analysis DOI: 10.2138/am.2010.3366

Single crystals of spinel and hausmannite having seven different compositions in the Mg[Al.sub.2][O.sub.4]Mg[Mn.sub.2][O.sub.4]-Mn[Mn.sub.2][O.sub.4] system were synthesized and structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. As predicted, tetrahedral and octahedral bond lengths increase with increasing substitutions of [Mn.sup.2+] for Mg and [Mn.sup.3+] for Al, respectively. A transition from cubic to tetragonal symmetry occurs at a critical concentration of [Mn.sup.3+] > 1.4 atoms per formula unit as a result of the Jahn-Teller distortion around octahedrally coordinated [Mn.sup.3+]. The present data in conjunction with data from the literature provide a basis for quantitative analyses of the cation polyhedral-distortion parameters and their variations in spinel- and hausmannite-type structures (Fd3m and [I4.sub.1]/amd, respectively). In contrast to the linear correlation between (octahedral quadratic elongation) and [[sigma].sup.2.sub.M] (octahedral bond-angle variance) observed for many silicates and isomorphic structures, these two distortion parameters are not correlated in multiple oxides with spinel- and hansmannite-type structures. By using a model of multiple linear regression, it is demonstrated that varies as a function of both [[sigma].sup.2.sub.M] and [[DELTA].sub.M] (octahedral bond-length distortion). The degree of octahedral distortion is significant in the spinel structures and is in fact comparable with that calculated for the hausmannite-type structures. The degree of octahedral distortion is related to steric effects in both spinel- and hausmannite-type structures, whereas the electronic effects caused by [Mn.sup.3+] account for the transition from cubic to tetragonal symmetry. Keywords: Crystal structure, spinel, hansmannite, XRD data, chemical analysis, polyhedral distortion DOI: 10.2138/am.2010.3336

The crystal chemistry of 13 spinel samples from the Somma-Vesuvius volcanic complex (Italy) was studied by crystal structural refinement and electron microprobe analysis, processing the data with a tested optimization model to obtain site populations. Five samples come from the volcanic xenoliths found in Pollena Quarry and belong to the deposits produced by the Pollena eruption of A.D. 472. All crystals are characterized by [Fe.sup.2+] [left and right arrow] Mg substitution and pertain to the Mg-rich portion of the spinel sensu stricto-hercynite join. The crystals show a partially inverted cation configuration with inversion degree ranging from 0.20-0.25. Aluminum contents characterize the crystal-chemistry: the unit-cell parameter decreases with increasing total Al and the M-O bond length decreases with increasing [sup.M]Al. Using a well-tested geothermometer based on the [sup.M]Al+[sup.T]Mg = [sup.T]Al+[sup.M]Mg intracrystalline exchange, closure temperatures were calculated for the Pollena Quarry spinels. Results range from 694 to 809 [degrees]C. The latter value is assumed to be representative of the temperature of the Pollena eruption and is in excellent agreement with that reported in the literature (800 [degrees]C) and estimated by experimental phase equilibria. Keywords: Spinel, crystal structure, chemical analysis, geothermometer, crystal chemistry, orderdisorder, Vesuvius DOI: 10.2138/am.2010.3401

Numerous petrologic studies have attempted to determine crystal growth rates in volcanic systems through several methods, including analyses of crystal size distributions in natural samples and decompression experiments on hydrous magmas. Experiments have revealed that rim growth on existing crystals will occur under a wide range of decompression conditions and is favored under conditions of low to moderate undercoolings over microlite nucleation, which has typically been the focus of decompression-induced crystallization studies. For this study, samples of eruptive clasts were collected from a Vulcanian explosion that occurred following the July 12-13, 2003 dome collapse of Soufri6re Hills volcano, Montserrat. Plagioclase phenocrysts were extracted and examined with secondary ion mass spectrometry (SIMS) depth profiling. Lithium inflection depths within the profiles, along with the observed time interval between the peak in the collapse decompression and the explosion that ejected the examined samples, were used to calculate the growth rates as a result of magma devolatilization, with an average of 8.3 x [10.sup.-8] mm/s. Anorthite content of the plagioclase rim growth indicates an average decompression magnitude of 40 MPa, inducing an undercooling of ~45[degrees]C that favors crystal growth over microlite nucleation. However, variability in the final anorthite contents suggests that not ali phenocrysts recorded an equilibrium composition reflecting accurate pressure conditions. In such events occurring over short timescales (< 10 h), lithium is a more reliable indicator of decompressioninduced growth than changing anorthite content due to lithium's rapid diffusivity. Keywords: Plagioclase, lithium, decompression, SIMS, Soufriere Hills DOI: 10.2138/am.2010.3292

The incommensurately modulated structure of the mineral natrite has been refined for the first time. Two single-crystal grains, Lv and Kh, from two different occurrences [Mt. Karnasurt, Lovozero massif(Lv), Kola peninsula, Russia, and the pegmatite of Mt. Koashva, Khibiny massif (Kh)], have been investigated at 293 and 120 K using synchrotron X-ray data. The average structures of both minerals are identical and the basic features &the structural modulations are similar to the synthetic [gamma]-[Na.sub.2]C[O.sub.3] phase previously published. The 7 (incommensurate) [right arrow] (lock-in) phase transition reported at low temperature for the synthetic compound was not observed down to 120 K in natural natrite. Crystalchemical aspects, especially about the second coordination sphere for the carbon atoms, are examined to explain the different structural behaviors observed at low temperature. The possible role played by the minor isomorphous substitutions in natural natrite specimens is also discussed. Keywords: Incommensurate structure, natrite, superspace, synchrotron X-ray data DOI: 10.2138/am.2010.3384

Olivine is the dominant component in coherent kimberlite rocks and related pyroclastic rocks. Quantitative characterization of olivine crystals in kimberlite rocks may be used to better understand kimberlite emplacement and eruption. Here, we construct the first complete olivine crystal size distribution (CSD) for magmatic or coherent kimberlite using two-dimensional image analysis techniques with a new method for scale-integration. Crystal size and frequency data are collected from polished slabs and thin sections, normalized to the largest scale of observation, and stereologically corrected to create a complete CSD covering the full range of observed olivine crystal sizes. Resulting CSDs show the following properties for olivine in crystal-rich interiors of intrusive coherent kimberlite in the A154N kimberlite pipe, Diavik, Northwest Territories: (1) 0.03-10.0 mm in diameter size range; (2) 46.7-51.2% modal crystal content; (3) modal% dominance by crystals >1 mm; (4) frequency dominance by crystals Measured size ranges and modal crystal content are consistent with previous reported data. Relative frequency and area ratios between crystals of different sizes and shape properties differ from previous assessments. Olivine CSDs are consistent with a power-law distribution over at least two orders of magnitude, and statistical parameters (power-law exponents, Inman parameters) suggest that apparent characteristic ranges are independent of crystal frequencies, modal abundance (area%), or sampling locale. These properties suggest olivine crystals may be a single population with a shared paragenesis, and not the end-product of a combination of two populations of olivine. On this basis, olivine CSDs and population parameters have the following uses: (1) to compare and discriminate among kimberlite facies and deposit types, and (2) to test models for olivine paragenesis. Keywords: Olivine, kimberlite, crystal size distribution, image analysis, emplacement, diamond DOI: 10.2138/am.2010.3277

This paper reports the occurrence and the crystal structure of fantappieite, a new member of the cancrinite-sodalite group of minerals from Torre Stracciacappe, Trevignano community (Rome, Latium, Italy). The mineral occurs within a volcanic ejectum consisting of dominant sanidine with minor plagioclase, biotite, augitic clinopyroxene, andradite, and iron oxides. Fantappieite (0.7 mm as largest size) is observed within miarolitic cavities of the rock as transparent colorless crystals, showing complex morphologies and striated faces. It is non-pleochroic and uniaxial negative, [n.sub.[omega]] = 1.5046(5) and [n.sub.[epsilon]] = 1.5027(5). [D.sub.calc] is 2.471 g/[cm.sup.3]. Fantappieite is trigonal, space group P[bar.3]; the cell parameters are: a = 12.8742(6), c = 87.215(3) [Angstrom], V= 12518.8(9) [[Angstrom].sup.3], Z= 1. The empirical chemical formula is: ([Na.sub.84.12][Ca.sub.30.00][K.sub.15.95][Fe.sub.0.19] [Ti.sub.0.13][Mn.sub.0.10][Mg.sub.0.09])([Si.sub.99.36] [Al.sub.98.64])[O.sub.396][(S[O.sub.4]).sub.30.24] [(C[O.sub.3]).sub.0.29][Cl.sub.0.84][F.sub.0.82]*5.18[H.sub.2]0, which corresponds to the ideal formula [[[Na.sub.82.5][Ca.sub.33] [K.sub.16.5].sub.[SIGMA]=132]([Si.sub.99][Al.sub.99] [0.sub.396])[(S[O.sub.4]).sub.33]*6[H.sub.2]0. The five strongest reflections in the X-ray powder pattern are [d in [Angstrom] (I %) (hkl)]: 3.70 (100) (3 0 0), 3.60 (80) (1 0 23), 2.641 (65) (0 0 33), 6.85 (60) (0 1 10), 6.40 (55) (1 1 0). The single-crystal FTIR spectrum rules out OH groups and shows the presence of [H.sub.2]O and CO2 molecules, as well. The structure can be described as a stacking sequence of 33 layers of six-membered rings of tetrahedra along the c axis. The stacking sequence is ACBACABACBACBACBCACBACBACBABCBACB ..., where A, B, and C represent the positions of the rings within the layers. This sequence gives rise to liottite, sodalite, and cancrinite cages, alternating along c. Sulfate groups occur within the liottite cages associated by Na, K, and Ca, while highly disordered sulfate groups are located within the sodalite cages. [H.sub.2]0 groups occur within the cancrinite cages, bonded to Ca and Na cations. Split positions are found for Na-Ca sites, and are related to disordering of the sulfate groups in the sodalite cages. Keywords: New minerals, fantappieite, crystal structure, IR spectroscopy, mechanical properties DOI: 10.2138/am.2010.3279

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

Fe-rich 'oxydravite' and dravite from the Late Proterozoic ophiolitic melange of the Arabo-Nubian Shield, located in Egypt and Saudi Arabia, were structurally and chemically characterized by using crystal structure refinement based on single-crystal X-ray diffraction data, electron microprobe analysis, and Mossbauer spectroscopy. Structural formulae obtained by optimization procedures indicate disordering of Al, Mg, and [Fe.sup.2+] over the Y and Z sites, and an ordering of [Fe.sup.3+] at Y. The disordering can be explained by the substitution mechanisms [2.sup.Y] Mg+[sup.Z]+[sup.W]OH = [2.sup.Y]Al+[sup.Z]Mg+[sup.W][O.sup.2-] and [2.sup.Y][Fe.sup.2+]+[sup.2][Fe.sup.3+]+[sup.W]OH = [2.sup.Y][Fe.sup.3+]+[sup.2][Fe.sup.2+]+[sup.W][O.sup.2], which are consistent with reducing the mismatch in dimensions between Y[O.sub.6] and Z[O.sub.6] octahedra. To explain the Mg-Al disordering process, as well as the occurrence of B at the T site in tourmaline, analogies have been drawn between the crystal structure of tourmaline and that of lizardite. A critical constraint in both structures is the geometrical fit of the six-membered tetrahedral ring with the attached group of three [YO.sub.6] octahedra. In tourmaline, the disordering of Mg and Al over Y and Z relieves the strain due to the misfit in dimensions of the larger triads of edge-sharing Mg[O.sub.6] octahedra and the smaller [Si.sub.6][O.sub.18] tetrahedral tings. In Al-rich tourmaline, where the octahedral cluster is smaller, the strain can be relieved by incorporating B in the tetrahedra. An opposite effect is observed by substitution of Al for Si at the tetrahedral site in Mg-rich tourmaline. Because the Al radius is intermediate between those of Mg and Si, Al plays an important structural role in accommodating the potential misfit between [YO.sub.6], Z[O.sub.6], and T[O.sub.4] polyhedra. The amount of Al and its distribution in the structure strongly affects the values of the unit-cell parameters of tourmaline and yields volume variations according to a quadratic model. This results from the effect of [sup.Z]Al combined with the occurrence of B at T in Al-rich tourmaline. [sup.Z]Al has a greater effect than [sup.Y]Al as long as Al does not fully occupy the Z site. Keywords: Chemical analysis, tourmaline, crystal structure, Mossbauer spectroscopy, order-disorder, XRD data DOI: 10.2138/am.2010.3357

The crystal structure, crystal chemistry, and low-temperature structural evolution of natural thomsonite from Terzigno, Somma-Vesuvins volcanic complex, Naples Province, Italy, have been investigated by means of in situ single-crystal X-ray diffraction, electron microprobe analysis in the wavelength dispersive mode, and Raman spectroscopy. Six structure refinements have been obtained at different temperatures: 295.5,248.0, 198.0, 148.0, 98.0, and 296.0 K (after the low-T experiments). The reflection conditions and the structure refinements prove that the crystal of thomsonite here investigated is orthorhombic with a = 13.0809(3), b = 13.0597(3), c = 6.6051(1) [Angstrom], V= 1128.37(14) [[Angstrom].sup.3], and space group Pbmn, which differs from thomsonite from different localities reported in previous studies (with a ~ 13.1, b ~ 13.06, c ~ 13.2 [Angstrom], and space group Pncn). The refined bond distances suggest that the Si/Al-distribution in the tetrahedral framework is fully 'disordered,' giving rise to the halving of the c axis relative to that found in 'ordered' thomsonites. The extra-framework population consists of: (1) one site about 50% occupied by Ca (labeled as 'Ca'); (2) one site occupied by Na (~70%) and Ca (~30%) (labeled as 'Na'); and (3) three water molecule sites ('WI,' 'W2,' 'W3'). The structure refinements allowed the location of all the proton sites, and the hydrogen-bonding scheme in the structure is provided. The low-temperature refinements show no significant change in the structure within the T-range investigated. The evolution of the unit-cell volume with T exhibits a continuous and linear trend, without any evident thermo-elastic anomaly, with thermal expansion coefficients [[alpha].sub.v] = [V.sup.-1]*[delta]V/[delta]T= 20(2)*[10.sup.-6] [K.sup.-1] (between 98.0 and 295.5 K). A list with the principal Raman active modes is provided and a comparison with the vibrational modes previously found for 'ordered' thomsonite is carried out. Keywords: Zeolite, thomsonite, Somma-Vesuvious, crystal chemistry, low temperature, single-crystal X-ray diffraction, single-crystal Raman spectroscopy DOI: 10.2138/am.2010.3353

Microlites in pumice fragments can record the rate of magma decompression and ascent, but only if none grow while those fragments cool in the atmosphere. For highly viscous silicate melts, such crystallization is unlikely, but more basic melts are known to crystallize rapidly, and thus could partially crystallize during cooling and overprint decompression textures. To examine whether post-fragmentation crystallization can occur, we examined two basaltic pumice clasts from the sub-Plinian April 1999 eruption of Shishaldin volcano, Alaska. Radial sectioning shows that microlite content doubles from rim to core in both, mainly from growth of plagioclase. Dendrite magnetite also increases greatly in content, but only within the larger pumice clast. Such radial textures demonstrate that crystallization occurred after fragmentation and before deposition (no welding occurred). Using a conductive cooling model coupled with a model for temperature in the eruption column, we estimate that rims of the pumice clasts cool to their glass-transition temperature in ~100-200 s, but their cores take ~500-2000 s to cool, which translates into cooling rates of ~0.2 to 2.5[degrees]C/s. Using a conservative assumption that all plagioclase nucleated before cooling began, we estimate that both short and long axes grew at ~4.8 ([+ or -] 2.7) x [10.sup.-7] cm/s. Such rates match those determined experimentally for basaltic melts at similar cooling rates. Magnetite grew only at the slowest cooling rates, and the rate of bulk magnetite crystallization equals that of plagioclase. Our results demonstrate that groundmass crystallization can occur in basic melts on the timescale of explosive eruptions, and so pumice clasts from such eruptions must be viewed with caution before being used to infer eruption dynamics. Keywords: Crystal growth, plagioclase, cooling, igneous petrology, basaltic pumice, microlites DOI: 10.2138/am.2010.3270

The crystal structure of a natural Na-rich gobbinsite from Bundoora, a northern suburb of Melbourne, Victoria, Australia [[([Na.sub.4.97] [K.sub.0.07][Ca.sub.0.48]).sub.[SIGMA]5.52][([Al.sub.5.62] [Si.sub.10.29]).sub.[SIGMA]15.91][O.sub.32]* 11.91[H.sub.2]O, Z = 1, a = 10.1035(15), b = 9.7819(10), c = 10.1523(9) [Angstrom], and V = 1003.37(20) [[Angstrom].sup.3], space group Pmnb (no. 62)], has been investigated by means of single-crystal X-ray diffraction, elemental CHN analysis, and electron microprobe analysis in the wavelength dispersive mode. For the first time, an anisotropic structural refinement has been performed on the basis of single-crystal X-ray diffraction data collected at 298 K, with: [R.sub.1](F) = 0.0608, 1362 unique reflections with [F.sub.o] > 4[sigma]([F.sub.o]), and 114 refined parameters. The residuals in the final difference-Fourier maps are less than [+ or -] 0.6 e-/[[Angstrom].sup.3]. Previous structure solutions based on powder diffraction data were performed in the space group [Pmn2.sub.1], with a significantly different description of the channels' content. In this study, the Si/Al distribution in the tetrahedral framework is found to be highly disordered. A complex configuration of the extra-framework population occurs, with two possible and mutually exclusive sites for cations (Na and Ca) and five independent sites partially occupied by water molecules (W1, W2, W2', W3, and WY). The coordination shell of the Na site is represented by a distorted polyhedron with coordination number CN = 6 (4 framework O atoms + 2 [H.sub.2]O molecules), with at least five possible mutually exclusive configurations, whereas the coordination shell of the Ca site is represented by a distorted polyhedron with CN = 7 (5 framework O atoms + 2 [H.sub.2]O molecules), with at least two possible mutually exclusive configurations. Keywords: Zeolite, gobbinsite, Bundoora (Victoria), crystal structure, single-crystal X-ray diffraction DOI: 10.2138/am.2010.3390

Optical absorption spectra of flux-grown single crystals in the spinel s.s.-magnesiochromite and gahnite-zincochromite solid solutions were recorded with the aim of exploring variations in local Cr-O bond distance as a function of composition. With increasing Cr contents, the crystals vary in color from pale red to intensely red to dark greenish. These variations are reflected in the optical spectra by the position and intensity of the two spin-allowed electronic d-d transitions in six-coordinated [Cr.sup.3+] at ~18 000 ([v.sub.1]) and 25 000 [cm.sup.-1] ([v.sub.2]). From the shift of the [v.sub.1] band position, a decrease in crystal field splitting, 10Dq, for six-coordinated [Cr.sup.3+] with increasing Cr contents is evident in both solid-solution series. Based on published Cr-O bond distances for the Cr[O.sub.6] polyhedra in magnesiochromite and zincochromite of 1.995 and 1.991 A, respectively, and applying the ligand field relationships, local Cr-O bond distances in gahnite and spinel with Cr contents at trace levels are determined to be 1.974(2) and 1.960(3) [Angstrom], respectively. These local Cr-O distances result in relaxation parameters (e) equal to 0.69(2) and 0.60(3) for Cr-O bonds in the Mg([[Al.sub.1-x][Cr.sub.x]).sub.2][O.sub.4] and Zn([[Al.sub.1-x] [Cr.sub.x]):[O.sub.4] series, respectively. However, the presently obtained Racah B values indicate increasing Cr-O bond covalency with increasing [Cr.sup.3+] contents. This suggests that color changes and accompanying 10Dq variations may be due to variations in Cr-O bond covalency along the two solid-solution series, without or with very minor local Cr-O bond distance variation. Consequently, the e values obtained from the present optical absorption spectra should be regarded as minimum values. Keywords: Crystal synthesis, optical spectroscopy, structural relaxation, spinel, gahnite, [Cr.sup.3+] DOI: 10.2138/am.2010.3388

Synthetic rubies were grown by the optical floating zone method and characterized by cathodoluminescence (CL) microscopy and spectroscopy in combination with microprobe analysis. The measured intensity of the [Cr.sup.3+]-induced CL of corundum is influenced by different parameters such as the sample thickness and orientation, the intensity of the beam current, and the quality of the sample surface. Furthermore, the spectral distribution of the CL emission changes with different concentrations of Cr in the corundum structure. Due to these effects, it is usually not possible to estimate the Cr content directly by using the measured CL intensity. However, we have developed an indirect method that is not significantly affected by these parameters. By using intensity ratios instead of measured intensities, a level of quantification of Ct in natural and synthetic corundum is now possible. Our study shows that the intensity ratio between the N-line at 701.6 nm and the sideband maximum at 713.2 nm displays a nearly linear dependence on the Cr concentration from ca. 100-300 ppm up to ca. 1.1 tool% [Cr.sub.2][O.sub.3]. These results give a possible approach to develop an optical-microscope-based CL spectroscopy for quantitative measurements of Cr in natural rubies and synthetic [alpha]-[Al.sub.2][O.sub.3] materials. Keywords: Quantitative cathodoluminescence, [alpha]-[Al.sub.2][O.sub.3], CL, rubies, crystal growth, floating zone technique DOI: 10.2138/am.2010.3291

Liversidgeite, ideally [Zn.sub.6][(P[O.sub.4]).sub.4] x 7[H.sub.2]O, is a new mineral from Block 14 Opencut, Broken Hill, New South Wales, Australia. The mineral occurs as white, thin, bladed crystals and as hemispherical aggregates of radiating crystals in cavities in sphalerite-galena ore. Associated minerals are anglesite, pyromorphite, greenockite, sulfur, and an unknown Zn phosphate sulfate. Individual crystals are up to 0.1 mm in length and 0.05 mm across. Liversidgeite is transparent to translucent, with a vitreous luster and a white streak. It is brittle with an irregular fracture, the Mohs hardness is ~3-3.5, and the observed and calculated densities are 3.21(2) and 3.28 g/[cm.sup.3], respectively. Chemical analysis by electron microprobe gave ZnO 54.62, MnO 0.49, PbO 0.18, [P.sub.2][O.sub.5] 32.62, [As.sub.2][O.sub.5] 0.65, S[O.sub.3] 0.35, [H.sub.2]O 14.04, total 102.95 wt%, with [H.sub.2]O content derived from the refined crystal structure. The empirical formula calculated on the basis of 23 O atoms is [Pb.sub.0.01][([Zn.sub.5.86][Mn.sub.0.06]).sub.[SIGMA]5.92] [([P.sub.4.01][As.sub.0.05][S.sub.0.04]).sub.[SIGMA]4.10][O.sub.16.20] x 6.8 [H.sub.2]O. Liversidgeite is triclinic, space group P[bar.1], with a = 8.299(1), b = 9.616(1), c = 12.175(1) [Angstrom], [alpha] = 71.68(1), [beta] = 82.02(1), [gamma] = 80.18(1)[degrees], V = 905.1(2) [[Angstrom].sup.3] (single-crystal data), and Z = 2. The six strongest lines in the X-ray powder diffraction pattern are [d([Angstrom]), (I), (hkl)]: 8.438 (80) (011), 3.206 (60) (01[bar.3]), 2.967 (75) (2[bar.1]2, 114), 2.956 (75) (21[bar.2]), 2.550 (85) (233, 2[bar.1]3), 2.537 (100) (22[bar.1],01[bar.4], 31[bar.1]). The crystal structure of liversidgeite was refined to an R1 index of 5.95% based on 3054 observed ([F.sub.o] > 4[sigma][F.sub.o]) reflections measured with MoK[alpha] X-radiation. The structure is based on two distinct, infinite zigzag chains of edge-sharing Zn[[phi].sub.6] ([phi] = unspecified anion) octahedra that extend in the a direction. The chains link to each other via common corners and also via corner-sharing P[O.sub.4] tetrahedra, forming sheets parallel to the (011) plane. The sheets link via [[Zn.sub.2][[phi].sub.8]] dimeric building units, comprising edge-sharing Zn[[phi].sub.5] trigonal bipyramids and Zn[[phi].sub.4] tetrahedra, resulting in an open framework. Large ellipsoidal channels extend along the a direction and are occupied by interstitial [H.sub.2]O groups and the H atoms of the [H.sub.2]O groups that coordinate to the Zn cations. An extensive network of hydrogen bonds provides additional linkage between the sheets in the structure, via the interstitial [H.sub.2]O groups. The topology of the liversidgeite structure is identical to that of synthetic, monoclinic [Zn.sub.2][Co.sub.4][(P[O.sub.4]).sub.4][([H.sub.2]O).sub.5] x 2[H.sub.2]O. Keywords: Liversidgeite, new mineral species, zinc phosphate, crystal structure, Broken Hill, New South Wales, Australia DOI: 10.2138/am.2010.3306

Aiolosite, ideally [Na.sub.4]Bi[(S[O.sub.4]).sub.3]Cl, or better [Na.sub.2]([Na.sub.2]Bi)[(S[O.sub.4]).sub.3]Cl, is a new sulfate mineral isotypic to apatite. It was found in an active medium-temperature intracrater fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. It occurs as acicular to slender prismatic crystals up to 0.5 mm long in an altered pyroclastic breccia, together with alunite, anhydrite, demicheleite-(Br), demicheleite-(Cl), bismuthinite, and panichiite. The symmetry is hexagonal (class 6/m), space group [P6.sub.3]/m, with a = 9.626(3), c = 6.880(3) [Angstrom], V = 552.1(3) [[Angstrom].sup.3], Z = 2. The habit is prismatic, terminated by the pinacoid or, more rarely, by a bipyramid. Aiolosite is colorless to white, with white streak; the luster vitreous. It is non-fluorescent. The calculated density is 3.589 g/[cm.sup.3]. The mineral is nonpleochroic, uniaxial (+), [n.sub.[omega]], = 1.59(1), [n.sub.[epsilon]] = 1.60(1), mean [n.sub.obs] = 1.593 (589 nm), [n.sub.calc] = 1.620. The chemical analysis gave [Na.sub.2]O 20.65, [K.sub.2]O 0.96, [Bi.sub.2][O.sub.3] 32.49, S[O.sub.3] 41.27, C1 4.02, Br 0.75, ([H.sub.2]O 0.57 from structure refinement), -O = (Cl + Br) 0.98 wt%, total 99.73, corresponding to the empirical formula calculated on the basis of 13 anions: [Na.sub.2][([Na.sub.1.95][K.sub.0.12][Bi.sup.3+.sub.0.83]).sub.[SIGMA] 2.90][S.sub.3.06][O.sub.12.08][[[Cl.sub.0.67][Br. sub.0.06][([H.sub.2]O).sub.0.19]].sub.[SIGMA]0.92]. The crystal structure has been refined to a final R index of 0.048. One of the two independent Ca sites of apatite is exclusively occupied by Na, and the other one by statistically distributed Na and Bi. The [SO.sup.2-.sub.4] anion replaces the P[O.sup.3-.sub.4] anion of apatite; the chloride anion is located in the partially occupied (s.o.f. = 0.81 ) position at x = 0, y = 0, z = 0. Whenever the chloride position is vacant, the position at x = 0, y = 0, z = 1/4 is occupied by water (s.o.f. = 0.19). The strongest 6 lines in the X-ray powder diffraction pattern [[d.sub.obs] ([Angstrom]) (I) hkl] are: 2.853 (100) (121), 2.775 (85) (112), 3.432 (45) (002), 1.965 (35) (222), 2.306 (25) (310), 4.787 (20) (110). Both the mineral and the mineral name have been approved by the IMA CNMNC (No. 2008-015). Keywords: Aiolosite, apatite structure, new mineral species, bismuth, sulfates, crystal structure, Vulcano Island, Aeolian Islands, Italy DOI: 10.2138/am.2010.3337

Metasideronatrite was obtained as the first dehydration product of sideronatrite, [Na.sub.2]Fe[(S[O.sub.4]).sub.2](OH) x 3[H.sub.2]O, from Sierra Gorda, Chile. The crystal structure of metasideronatrite was solved by direct methods and refined by full-matrix least-squares to R = 0.039, using 574 independent reflections with I > 3.0[sigma](I). It is orthorhombic, space group Pbnm, with a = 7.3959(8), b = 16.0979(15), c = 7.1607(8) [Angstrom], V = 852.5(2) [[Angstrom].sup.3], Z = 4. The crystal-chemical formula derived from this structural study is [Na.sub.2]Fe[(S[O.sub.4]).sub.2](OH) x [H.sub.2]O. The backbone of the structure is the same as that in sideronatrite: infinite [[[Fe.sup.3+][(S[O.sub.4]).sub.2](OH)].sup.2-] chains of interconnected octahedra and tetrahedra parallel to the c axis. These chains are linked primarily by Na atoms to build a 3-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. Another prominent feature of the structure is the arrangement of distorted (Na[O.sub.5][H.sub.2]O) octahedra, which alternately share one edge and one face to form columns parallel to the [[Fe.sup.3+][(S[O.sub.4]).sub.2](OH)] chains. Subsidiary intra-chain bonds are provided by H atoms belonging to OH- groups shared by adjacent Fe octahedra, and to the unique water molecule shared between two adjacent (Na[O.sub.5][H.sub.2]O) octahedra. At normal conditions of relative humidity (RH) and temperature (i.e., RH > 60% and T < 40[degrees]C), metasideronatrite rehydrates rapidly to sideronatrite. The structure solution has allowed us to: (1) investigate the strong relation between sideronatrite and metasideronitrite; (2) elucidate the mechanism involved in the transformation ofmetasideronatrite into the order/disorder (OD) structure of sideronatrite; and (3) get insight into the stability of this mineral from the valence-matching principle applied to the main structural unit [[[Fe.sup.3+](S[O.sub.4])2(OH)].sup.2] and [Na.sup.+] interstitial species. The weak hydrogen bonds and the particular arrangement of the face-sharing adjacent [Na[O.sub.5]([H.sub.2]O)] octahedra are the main factors affecting the stability of metasideronatrite. Keywords: Metasideronatrite, structure, crystal chemistry, dehydration, sideronatrite DOI: 10.2138/am.2010.3332

High-pressure and room-temperature single-crystal X-ray diffraction (XRD) studies have been performed on crystals of a natural pigeonite sample with composition ca. [Wo.sub.10][En.sub.43][Fs.sub.47] using diamond-anvil cells. The unit-cell parameters were determined at 18 different pressures up to about 6 GPa. A first-order [P2.sub.1]/c-C2/c phase transition was found between 3.5 and 3.6 GPa, associated with the disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 1.7%) in the unit-cell volume. At the transition, a small hysteresis (~0.3 GPa) was observed. A third-order Birch-Murnaghan equation of state (BM3-EoS) fit to the 10 P-V data of the low-P phase yielded [V.sub.0] = 431.93(2) [[Angstrom].sup.3], [K.sub.T0] = 96.8(8) GPa and K' = 8.5(6). A second-order Birch-Murnaghan EoS fit to the 8 P-V data (between 3.6 and 6 GPa) of the C2/c high-P phase yielded [V.sub.0] = 423.6(1) [[Angstrom].sup.3] and [K.sub.T0] = 112.4(8), indicating that the high-P C2/c phase is significantly stiffer than the low-P phase. In a separated experiment with crystals of the same sample, intensity data were collected and crystal structures were refined at 13 pressures up to 9.4 GPa. The M1-O and M2-O mean bond lengths of the low-P [P2.sub.1]/c phase decrease by 0.7 and 2.1%, respectively. The two non-equivalent A and B tetrahedral chains become more kinked with pressure, with a reduction of their angle by 2.2 and 5.1%, respectively. At the transition the A-chain changes sense of rotation and both chains become equivalent and more kinked, with a further reduction of their angle by 2.5% up to 9.4 GPa. Strain calculations have been performed and the evolution of the spontaneous strain and the order parameter variation with pressure are discussed, considering geometrical parameters of the structure and comparing our results with the available data for other compositions. Keywords: Pigeonite, high-pressure, single crystal XRD, diamond-anvil cell, phase transition, spontaneous strain DOI: 10.2138/am.2010.3175

The crystal structure and pressure influence (between 0-6 GPa) on 2M1 muscovite have been calculated by quantum-mechanical methods based on density functional theory (DFT) with optimized numerical LCAO basis sets and norm-conserving pseudopotentials. Tensions between 0.8 and 0 GPa have been also studied. Volumes as a function of pressure, computed from the generalized gradient approximation, are closer to the experimental data than volumes calculated from the local density approximation. The crystal structure, bond distances, and main geometrical features agree with previous experimental values. A third-order Birch-Murnagham equation is fitted, giving a bulk modulus of 60.1 GPa, which reasonably agrees with the experimental data. Axis compressibilities are slightly smaller than those of the experimental data. The most compressible axis is the c axis. Bond strains, angles, the main geometrical features, and polyhedral strains are studied as a function of pressure, and these vary according to the experimental behavior. Tetrahedral and angles and corrugation show an oscillating behavior in the range of pressures used. The most important compressibilities are those related to the interlayer space, as it corresponds to the weakest bonding in the structure. The highest compressibility in the T-O-T layer along the [001] direction is determined by the octahedral sheet thickness. The compressibilities along the a and b axes are determined by the tetrahedra, as the most compressible polyhedra, and the [alpha] angle. Therefore, with our results the utility of periodic DFT methods for studying crystal structure and the effect of hydrostatic pressure on [2M.sub.1] muscovite are once again validated, and they are suitable to describe the compression of the crystal structure in detail. Keywords: Muscovite, crystal structure, pressure, DFT, equations of states, compressibility, bulk modulus DOI: 10.2138/am.2010.3035

Single-crystal diffraction data collected for Ca[Fe.sub.2][O.sub.4] at high pressure reveal above 50 GPa an isosymmetric phase transition (i.e., no change in symmetry) marked by a volume decrease of 8.4%. X-ray emission spectroscopic data at ambient and high pressure confirm that the nature of the phase transition is related to the [Fe.sup.3+] high-spin/low-spin transition. The bulk modulus [K.sub.0] calculated with a Birch Murnaghan EoS (K' = 4) is remarkably different [[K.sub.0] = 159(2) GPa for Ca[Fe.sub.2][O.sub.4] 'high spin' and [K.sub.0] = 235(10) GPa for Ca[Fe.sub.2][O.sub.4] 'low spin']. Crystal structure refinements reveal a decrease of 12% of the [Fe.sup.3+] crystallographic site volume. The geometrical features of the low-spin [Fe.sup.3+] crystallographic site at high pressure (bond lengths, volume) indicate a relevant decrease of [Fe.sup.3+]-O bond lengths, and the results are in agreement with tabulated values for crystal radii of [Fe.sup.3+] in high- and low-spin state. The reduced crystal size of [Fe.sup.3+] in the low-spin state suggest that in lower mantle assemblages, [Fe.sup.3+] partitioning in crystallographic sites should be strongly affected by the iron spin state. Keywords: Ca[Fe.sub.2][O.sub.4], high pressure, spin transition, single crystal DOI: 10.2138/am.2010.3347

Lapeyreite, ideally [Cu.sub.3]O[[As[O.sub.3](OH)].sub.2] x 0.75 [H.sub.2]O, was found in the old copper mines of Roua (Alpes-Maritimes, France). It is invariably in intimate association with trippkeite. Other associated minerals are olivenite, malachite, gilmarite, comubite, connellite, theoparacelsite, brochantite, cuprite, native copper, algodonite, and domeykite. Lapeyreite occurs in geodes of cuprite (0.5 mm diameter) as aggregates formed by perfect elongate rectangular crystals (up to 0.2 x 0.05 x 0.01 mm in size), acicular fibrous crystals or powdery masses. The mineral is translucent (transparent in thin fragments), dark pistachio-green. It has a vitreous to adamantine luster and yellowish green streak. The tenacity is brittle and the fracture conchoidal. The rectangular crystals are elongate parallel to [010], flattened on (001), and have a perfect cleavage on {001}, and good cleavage on {100}. All crystals, without exception, are twinned on the (001) plane. The recognizable crystal forms are {100}, {010}, and {001}. In transmitted light, the mineral is pistachio-green, with strong pleochroism: X = light yellow-green, Y = pistachio-green, Z = dark pistachio-green; dispersion: r > v, medium. Lapeyreite is biaxial (+), with [n.sub.[alpha]] ~ 1.82, [n.sub.[beta]] ~ 1.85, [n.sub.[gamma]] ~ 1.90 (for [lambda] = 589 nm) x [2V.sub.means] = 76[degrees] (universal stage), [2V.sub.calc] = 77[degrees]. The optical orientation is [X.sub.[conjunction]] c ~ 12[degrees], Y = a, Z = b. The mean chemical composition determined by electron microprobe is (wt%): CuO 46.49, [As.sub.2][O.sub.5] 45.82, [H.sub.2]O (from crystal structure analysis) 6.30, total 98.61. The empirical formula calculated on the basis of nine structural O atoms (excluding molecular water) is [Cu.sub.2.96][As.sub.2.01][O.sub.6.99][(OH).sub.2.01] x 0.77[H.sub.2]O. Lapeyreite is monoclinic, C2/m, a = 19.158(3), b = 2.9361 (6), c = 9.193(2) [Angstrom], [beta] - 103.26(1)[degrees], V=503.32(6) [[Angstrom].sup.3], Z = 8/3. The calculated density is 4.385 g/[cm.sup.3] (based on the empirical formula). The strongest X-ray powder-diffraction lines are [d([Angstrom])(I)(hkl)]: 7.36 (30) ([bar.2]01), 5.842 (40)(201), 4.476 (35)(002), 3.173 (90)([bar.6]01), 2.984 (100)(003), 2.883 (30)([bar.6]02), 2.484 (80) (311), 2.396 (40)(112, [bar.8]01), and 2.337 (35)(800). The crystal structure of lapeyreite was solved by direct methods (MoK[alpha] radiation) and refined on [F.sup.2] using all 617 observed reflections to R = 0.069. The structure of lapeyreite is formed by a three-dimensional network of Cu[O.sub.5] square pyramids and As[O.sub.4] tetrahedra with a water molecule in structural cavities. This structure shows some similarities to that of theoparacelsite. The mineral is named in honor of Laurent Lapeyre, an eminent mineral collector and expert on Roua minerals. Keywords: Lapeyreite, new mineral, crystal structure, copper arsenate, Roua mines, Alpes-Maritimes, France DOI: 10.2138/am.2010.3225

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

The crystal structure of a 6C pyrrhotite from Mponeng Mine, South Africa, has been refined using starting atomic parameters postulated by Koto et al. (1975). This pyrrhotite is monoclinic and is described in the non-standard space group Fd, so that the metrically orthorhombic unit-cell shape is preserved. The cell symmetry is monoclinic with dimensions a = 6.897(2), b 11.954(3), c = 34.521 (7), and with [beta] 90.003(4)[degrees]. The structure has been refined with anisotropic displacement parameters to R = 0.029 using 1493 observable reflections with 1 > 2[sigma](/) and R = 0.034 for all 1800 reflections. The internal [R.sub.int] is 0.023 for the symmetrically equivalent reflection data. The composition of the crystal, as determined by electron microprobe analysis is [Fe.sub.10.91] [Ni.sub.0.05][S.sub.12]. The crystal structure resembles that of the 5C pyrrhotite in that the atomic positions of the Fe and S atoms are arranged in a very similar fashion, the only real difference being the arrangement of partially occupied iron sites. The coordination of the iron atoms is octahedral and short Fe-Fe distances along the c-axis are also encountered in this structure. The vacancy distribution is similar to that postulated by Koto et al. (1975) and is characterized by the stacking of two approximately half-occupied sites, followed by an essentially fully occupied layer. This is however a simplification and results in a composition that is too metal-rich. Two other slightly defect sites with occupancies of 0.90 and 0.87 are also present in the structure, and all layers contain both fully occupied and partially occupied sites. Refinement of the occupancies of all these sites gives rise to an atomic distribution that resembles the measured composition most closely, and is refined as [Fe.sub.10.99][S.sub.12]. The powder diffraction pattern of this structure is compared to the very similar pattern of the 5C structure. The crystal structure is also given in the more conventional Cc setting so as to be compatible with the available crystallographic software that cannot normally accommodate the Fd space group. Keywords: Pyrrhotite-6C, crystal structure, non-stoichiometry, iron sulfide, superstructure DOI: 10.2138/am.2010.3266

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

Large single crystals of stishovite were successfully synthesized at 11 GPa from a silica solution in water. The potential of both slow cooling and thermal gradient methods were examined. The thermal gradient method provided crystals of 0.8 x 0.8 x 1.3 mm in size grown at 1350 [degrees]C and a thermal gradient of 50 [degrees]C/mm using stishovite as a silica source. The use of quartz as a source resulted in the appearance of numerous stishovite crystals in the solution interior resulting in diminished space for the growth of large crystals. This can be explained by a significant difference in the solubility of metastable quartz and stishovite in water, estimated to be 85.3 and 5.6 wt% Si[O.sub.2] at 1000 [degrees]C and 11 GPa, respectively. Crystals up to 0.8 x 1.3 x 1.5 mm were grown by the slow cooling method in the system Si[O.sub.2] + 14.7 wt% [H.sub.2]O as temperature was decreased from 1600 to 1000 [degrees]C with a cooling rate of 2 [degrees]C/min. The size of single crystals obtained was large enough to carry out silicon self-diffusion experiments, which were performed at a pressure of 14 GPa and temperatures from 1400 to 1800 [degrees]C. The lattice diffusion coefficients along the [110] and [00l] directions can be expressed as [D.sub.[110]] ([m.sup.2]/s) 4.10 x [10.sup.-12] exp [-322 (kJ/mol)/RT] and [D.sub.[001]] ([m.sup.2]/s) = 5.62 x [10.sup.-12] exp [- 334 (kJ/mol)/RT], respectively, where R is the gas constant and T is the absolute temperature. Keywords: Stishovite, single-crystal growth, high pressure, aqueous fluid, silica solubility, diffusion DOI: 10.2138/am.2010.3255