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The Windjana drill sample, a sandstone of the Dillinger member (Kimberley formation, Gale Crater, Mars), was analyzed by CheMin X-ray diffraction (XRD) in the MSL Curiosity rover. From Rietveld refinements of its XRD pattern, Windjana contains the following: sanidine (21% weight, ~Or95); augite (20%); magnetite (12%); pigeonite; olivine; plagioclase; amorphous and smectitic material (~25%); and percent levels of others including ilmenite, fluorapatite, and bassanite. From mass balance on the Alpha Proton X-ray Spectrometer (APXS) chemical analysis, the amorphous material is Fe rich with nearly no other cations-like ferrihydrite. The Windjana sample shows little alteration and was likely cemented by its magnetite and ferrihydrite. From ChemCam Laser-Induced Breakdown Spectrometer (LIBS) chemical analyses, Windjana is representative of the Dillinger and Mount Remarkable members of the Kimberley formation. LIBS data suggest that the Kimberley sediments include at least three chemical components. The most K-rich targets have 5.6% K2O, ~1.8 times that of Windjana, implying a sediment component with >40% sanidine, e.g., a trachyte. A second component is rich in mafic minerals, with little feldspar (like a shergottite). A third component is richer in plagioclase and in Na2O, and is likely to be basaltic. The K-rich sediment component is consistent with APXS and ChemCam observations of K-rich rocks elsewhere in Gale Crater. The source of this sediment component was likely volcanic. The presence of sediment from many igneous sources, in concert with Curiosity's identifications of other igneous materials (e.g., mugearite), implies that the northern rim of Gale Crater exposes a diverse igneous complex, at least as diverse as that found in similar-age terranes on Earth.

The Mars Science Laboratory (MSL) rover Curiosity has documented a section of fluvio-lacustrine strata at Yellowknife Bay (YKB), an embayment on the floor of Gale crater, approximately 500 m east of the Bradbury landing site. X-ray diffraction (XRD) data and evolved gas analysis (EGA) data from the CheMin and SAM instruments show that two powdered mudstone samples (named John Klein and Cumberland) drilled from the Sheepbed member of this succession contain up to ~20 wt% clay minerals. A trioctahedral smectite, likely a ferrian saponite, is the only clay mineral phase detected in these samples. Smectites of the two samples exhibit different 001 spacing under the low partial pressures of H2O inside the CheMin instrument (relative humidity

The structure of opal has long fascinated scientists. It occurs in a number of structural states, ranging from amorphous to exhibiting features of stacking disorder. Opal‐CT, where C and T signify cristobalite‐ and tridymite‐like interstratification, represents an important link in the length scales between amorphous and crystalline states. However, details about local atomic (dis)order and arrangements extending to long‐range stacking faults in opal polymorphs remain incompletely understood. Here, a multilevel modeling approach is reported that considers stacking states in correlation with the abundance of C and T segments as a high‐level structural parameter (i.e. not each atom). Optimization accounting for inter‐tetrahedral bond lengths and angles and the regularity of the silicate tetrahedra is included as lower levels of structural parameters. Together, a set of parameters with both coarse‐grained and atomistic features for different levels of structural details is refined. Structural disorder at the ∼10–100 Å distance scale is evaluated using experimental pair distribution function and diffraction datasets, comparing peak intensities, widths and asymmetry. This work presents a complete multilevel structural description of natural opal‐CT and explains many of the unusual features observed in X‐ray powder diffraction patterns. This modeling approach can be adopted generally for analyzing layered materials and their assembly into 3D structures. [ABSTRACT FROM AUTHOR]

In this work, the crystal structure of a natural specimen of the "Messbach-type" variscite from Tooele Co. (Utah, U.S.A.) was determined, and the dehydration process leading to the transition to a new AlPO SB 4 sb phase was monitored at high temperature. Crystal structure description of variscite 2O and comparison with variscite 1O Like variscite I 1O i , the variscite I 2O i crystal structure belongs to the family of framework 3D MT structures in which octahedra (M) and tetrahedra (T) are linked by bridging O atoms ([30]). The Al-coordination change from octahedral to tetrahedral that accompanies dehydration, clearly demonstrated by the SP 27 sp Al NMR data, confirms the removal of the Al-bound H SB 2 sb O molecules as the dehydration mechanism, transforming the variscite octahedral-tetrahedral framework to a purely tetrahedral framework. Keywords: Variscite; X-ray powder diffraction; charge-flipping; nuclear magnetic resonance; polytypism; AlPO4 EN Variscite X-ray powder diffraction charge-flipping nuclear magnetic resonance polytypism AlPO4 1385 1395 11 07/05/22 20220701 NES 220701 Introduction Interest in hydrated aluminophosphates and in compounds that derive from their dehydration spans a wide spectrum of disciplines. [Extracted from the article]

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

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

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

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.006 Byline: Jochen Janchen (a)(b), Richard V. Morris (c), David L. Bish (d), Mareike Janssen (a), Udo Hellwig (a) Keywords: Mars; surface; Mineralogy Abstract: The recent detection of up to [approximately equal to]10 wt% water-equivalent H heterogeneously distributed in the upper meter of the equatorial regions of the martian surface and the presence of the 3-[mu]m hydrations feature across the entire planet raises the question whether martian surficial dust can account for this water-equivalent H. We have investigated the H.sub.2O and CO.sub.2 adsorption properties of palagonitic dust ( Author Affiliation: (a) TFH Wildau (University Applied Sciences), BahnhofstraAe, 15745 Wildau, Germany (b) TFH Wildau, c/o ZeoSolar e.V., Volmerstr. 13, 12489 Berlin, Germany (c) NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA (d) Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, USA Article History: Received 3 December 2007; Revised 15 September 2008; Accepted 2 December 2008

The crystal structures of natrolite and its dehydrated high-temperature phases ([alpha]1- and ([alpha]2-metanatrolite) have been determined from powder X-ray diffraction measurements as a function of temperature and partial pressure of water ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) to characterize the phase transition behavior. The evolution of crystal structure as a function of temperature shows two different phase transitions, depending on the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], with [alpha]1-metanatrolite occurring at elevated [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [alpha]2-metanatrolite occurring at low [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Our discovery of [alpha]2-metanatrolite implies the existence of more than one transition mechanism, which we correlate with the migration of [Na.sup.+] ions and the rate of evolution of [H.sub.2]O molecules. The transition behavior is rationalized in terms of two cooperating mechanisms: (1) dehydration-induced processes, which determine the phase transition temperature; and (2) thermally induced processes, which determine how the framework and its extraframework cations are modified. Keywords: Phase transition, natrolite, crystal structure, Rietveld refinement, TGA

Rietveld refinements using synchrotron powder X-ray diffraction data were used to study the crystal structure and dehydration behavior of sepiolite from Durango, Mexico. The room-temperature (RT) sepiolite structure in air compares well with previous models but reveals an additional zeolitic [H.sub.2]O site. The RT structure under vacuum retained only ~1/8 of the zeolitic [H.sub.2]O and the volume decreased by 1.3%. Real-time, temperature-resolved synchrotron powder X-ray diffraction data and Rietveld refinements were used to investigate the behavior of the sepiolite structure from 300 to 925 K. Rietveld refinements revealed that most of the zeolitic [H.sub.2]O is lost by ~390 K, accompanied by a decrease in the a and c unit-cell parameters. Above ~600 K the sepiolite structure folds as one-half of the crystallographically bound [H.sub.2]O is lost. Rietveld refinements of the 'anhydrous' sepiolite structure reveal that, in general, unit-cell parameters a and b and volume steadily decrease with increasing temperature; there is an obvious change in slope at ~820 K suggesting a phase transformation coinciding with the loss of the remaining bound [H.sub.2]O molecule. Keywords: Sepiolite, Rietveld, synchrotron, powder diffraction