Global Rietveld refinement

Shankland, Kenneth

doi:10.6028/jres.109.011

Cited by 20 publications

(17 citation statements)

References 14 publications

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“…Errors in the mineral abundances from the covariance matrix of the least--squares fit are less than ~0.5% (1--σ) for all refinement results reported here, though the true errors in the refined abundances may be somewhat higher. The weighted profile residual of the Rietveld refinements are all less than ~10%, and while there is no rigorous standard for the maximum Rwp that constitutes an acceptable fit, an Rwp value of ≤10 % is considered reasonable by many authors (Bish and Post, 1993;Young, 1993;Gualtieri, 2000;Shankland, 2004;Pecharsky and Zavalij, 2005).…”

Section: Rietveld Refinement Resultsmentioning

confidence: 99%

“…Rietveld refinement uses a numerical model of a diffraction experiment, (including the incident radiation, the instrument, and the structure and composition of the scattering matter) to create a simulated diffraction pattern. The simulated diffraction pattern is then compared with the measured diffractogram for that sample, and nonlinear least--squares optimization of the model parameters (instrumental parameters, abundances and crystallographic parameters of the mineral(s) present) carried out to find the best fit of the model parameters to the diffractogram (Rietveld, 1969;Young et al, 1977;Young, 1993;Shankland, 2004). Rietveld refinement is capable of accurately quantifying the modal mineralogy of complex mixtures (e.g., Bish and Post, 1993;Gualtieri, 2000;Shankland, 2004;Wilson et al, 2006).…”

Section: Rietveld Refinement Methodsmentioning

confidence: 99%

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Chelyabinsk meteorite explains unusual spectral properties of Baptistina Asteroid Family

Reddy¹,

Sanchez²,

Bottke³

et al. 2014

Icarus

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We investigated the spectral and compositional properties of Chelyabinsk meteorite to identify its possible parent body in the main asteroid belt. Our analysis shows that the meteorite contains two spectrally distinct but compositionally indistinguishable components of LL5 chondrite and shock blackened/impact melt material. Our X--ray diffraction analysis confirms that the two lithologies of the Chelyabinsk meteorite are extremely similar in modal mineralogy. The meteorite is compositionally similar to LL chondrite and its most probable parent asteroid in the main belt is a member of the Flora family. Our work confirms previous studies (e.g., Vernazza et al. 2008;de León et al., 2010;Dunn et al., 2013), linking LL chondrites to the Flora family. Intimate mixture of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides a spectral match with (8) Flora, the largest asteroid in the Flora family. The Baptistina family and Flora family overlap each other in dynamical space. Mineralogical analysis of (298) Baptistina and 11 small family members shows that their surface compositions are similar to LL chondrites, although their absorption bands are subdued and albedos lower when compared to typical S--type asteroids. A range of intimate mixtures of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides spectral matches for all these BAF members. We suggest that the presence of a significant shock/impact melt component in the surface regolith of BAF members could be the cause of lower albedo and subdued absorption bands. The conceptual problem with part of this scenario is that impact melts are very rare within ordinary chondrites. Of the 42,000 ordinary chondrites, less than 0.5% (203) of them contain impact melts. A major reason that impact melts are rare in meteorites is that high impact velocities (V > 10 km/s) are needed to generate the necessary shock pressures and temperatures (e.g., Pierazzo and Melosh 1998) unless the target material is highly porous. Nearly all asteroid impacts within the main belt are at ~5 km/s (Bottke et al., 1994), which prevents them from producing much impact melt unless they are highly porous. However, shock darkening is an equally efficient process that takes place at much lower impact velocities (~2 km/s) and can cause the observed spectral effects. Spectral effects of shock darkening and impact melt are identical. The parent asteroid of BAF was either a member of the Flora family or had the same basic composition as the Floras (LL Chondrite). The shock pressures produced during the impact event generated enough impact melt or shock blackening to alter the spectral properties of BAF, but keep the BAF composition largely unchanged. Collisional mixing of shock blackened/impact melt and LL5 chondritic material could have created the Baptistina Asteroid Family with composition identical to those of the Floras, but with subdued absorption bands. Shock darkening and impact melt play an important role in altering the spectral and alb...

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Section: Rietveld Refinement Resultsmentioning

confidence: 99%

Section: Rietveld Refinement Methodsmentioning

confidence: 99%

Chelyabinsk meteorite explains unusual spectral properties of Baptistina Asteroid Family

Reddy¹,

Sanchez²,

Bottke³

et al. 2014

Icarus

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“…A full refinement of atomic positions was not attempted as, generally, the position, orientation and conformation of the molecular fragments have much greater impact on structure solution than bond lengths. Varying bond lengths within "chemically sensible" parameters usually has small impact on the cost function used for Rietveld refinement [12]. Moreover, in order to even attempt a full refinement, better data, for example collected using synchrotron radiation, would be necessary and, for molecular fragments of this complexity, probably not sufficient.…”

Section: Crystal Structure Determinationmentioning

confidence: 99%

Reversibly changing a painkiller structure: A hot topic for a cold case—Ibuprofen lysine salt

Vladiskovic

Masciocchi

2015

Journal of Pharmaceutical and Biomedical Analysis

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“…Rietveld refinement uses nonlinear least squares optimization to fit a calculated diffraction pattern to measured powder diffraction data [ Bish and Post , 1993; Rietveld , 1967; Shankland , 2004; Young et al , 1977]. The theoretical diffraction pattern is a function of all relevant geometrical, specimen and experimental parameters.…”

Section: Powder X‐ray Diffraction and Rietveld Refinementmentioning

confidence: 99%

“…In this study, we characterize EL and EH chondrites spanning the full range of textural alteration grades using X‐ray diffraction (XRD) and reflectance infrared (IR) spectroscopy. The XRD data are used to determine quantitative mineral abundances by Rietveld refinement [e.g., Bish and Post , 1993; Gualtieri , 2000; Pecharsky and Zavalij , 2005; Scarlett et al , 2002; Shankland , 2004]. Refined mineral abundances are then used to calculate grain densities.…”

Section: Introductionmentioning

confidence: 99%

Mineralogical and spectroscopic investigation of enstatite chondrites by X‐ray diffraction and infrared reflectance spectroscopy

et al. 2010

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[1] The mineralogy and infrared reflectance spectra of 13 Enstatite (E) chondrite meteorite finds spanning the full range of textural alteration grades in both EL and EH classes have been investigated. Rietveld refinement of high-resolution powder X-ray diffraction (XRD) data was used to determine quantitative major mineral abundances. Sample-correlated mid-infrared (2.0 to 25.0 mm; 4500 cm −1 to 400 cm −1 ) reflectance infrared spectra were collected for each meteorite. Spectral features due to the fundamental lattice vibrations of the silicates, primarily enstatite, dominate the spectra of these meteorites over most of the spectral range investigated. The spectral features related to primary (i.e., pre-terrestrial) mineralogy include fundamental stretching and bending lattice modes (∼8.3-25.0 mm; 1200-400 cm), overtones and combinations of the fundamental modes (∼4.5-6.1 mm; 2200-1650 cm −1 ), and the principle Christensen feature (∼8.3 mm; 1200 cm −1 ). Terrestrial weathering products including Fe-oxyhydroxides, gypsum, and carbonates occur in most of these meteorites and contribute to some spectral features: particularly an asymmetric feature near ∼2.6 to 3.8 mm (3800 to 2600 cm

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Global Rietveld refinement

Cited by 20 publications

References 14 publications

Chelyabinsk meteorite explains unusual spectral properties of Baptistina Asteroid Family

Chelyabinsk meteorite explains unusual spectral properties of Baptistina Asteroid Family

Reversibly changing a painkiller structure: A hot topic for a cold case—Ibuprofen lysine salt

Mineralogical and spectroscopic investigation of enstatite chondrites by X‐ray diffraction and infrared reflectance spectroscopy

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