Quantitative phase analysis of bentonites by the rietveld method

Abstract

Thirty six bentonite samples from 16 different locations were examined in order to demonstrate the applicability of a new Rietveld description approach for quantitative phase analysis. X-ray diffraction patterns of the bulk material were obtained and analyzed by the Rietveld method. The samples contain up to ten different minerals, with dioctahedral smectite as the major component. A model for turbostratic disorder of smectites was formulated inside a structure-description file of the Rietveld program BGMN. The quality of the refinements was checked using an internal standard mineral (10.0 or 20.0 wt.% corundum) and by cross-checking results with X-ray fluorescence (XRF) data. The corundum content was reproduced with only small deviations from the nominal values. A comparison of the chemical composition obtained by XRF and the composition as re-calculated from quantitative Rietveld results shows a satisfactory agreement, although X-ray amorphous components such as volcanic glasses were not considered. As a result of this study, the Rietveld method combined with the new structure model for turbostratic disorder has proven to be a suitable method for routine quantitative analysis of bentonites with smectites as the dominant clay minerals.

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

“…Quantification was performed by Rietveld refinement, using the software TOPAS and BGMN, for patterns recorded with the Bruker D5000 and the Huber MC9300, respectively. We followed procedures as published in Kahle et al (2002) and Ufer et al (2008). Diffractograms were recorded with 2 ranging from 2 • to 92 • , with long counting times.…”

“…Intracrystalline plasticity of phyllosilicates is proposed as a deformation mechanism in clay (Urai and Wong, 1994). However, it is the most difficult one to observe: permanent deformation without fracturing is thought to occur mostly along the clays' (001) basal planes, producing a crystal lattice hardly distinguishable from the educt (Warr and Cox, 2001;Warr et al, 2014).…”

Drilling and sampling a natural CO2 reservoir: Implications for fluid flow and CO2-fluid–rock reactions during CO2 migration through the overburden

“…Quantitative phase analysis is performed by Rietveld refinement. BGMN software is used, 483 with customised clay mineral structure models (Ufer et al, 2008). In-situ CO 2 concentrations and fluid pH within the Navajo Sandstone were measured on 499 pressurized downhole fluid samples collected during drilling (Table 1).…”

The lateritic profile of Balkouin, Burkina Faso: Geochemistry, mineralogy and genesis

“…Nontronite is considered as a phase with 'partial or no known crystal structure' (PONKCS); due to swelling, its chemistry can be altered consequent to cations substitution and assorted hydration states. This implies a significant increase in the c 0 cell parameter (caused by hydration of the interlayer cations) with consequent variation of the (001) basal reflection in the range 9.7-15 Å (Ufer et al, 2008;Bayliss, 1989;Besson et al, 1983;Eggleton, 1977;Keeling et al, 2000;Tsipursky and Drits, 1984;Dekov et al, 2007) or even more (Scarlett et al, 2011). Furthermore, the XRPD signature of nontronite presents asymmetric peak shapes and anisotropic peak broadening (see Figure 8b; sample BVI -reflection labeled 'Nntr') due to turbostratic disorder, namely a random rotation/translation of the individual layers relative to each other (Warren, 1941;Biscoe and Warren, 1942).…”