Crystal structure model development for soil clay minerals – II. Quantification and characterization of hydroxy-interlayered smectite (HIS) using the Rietveld refinement technique

Review Article. What are the nature and formation conditions of hydroxy‐interlayered minerals (HIMs) in soil?

“…Apart from this, segregation effects seem common, at least for synthetic HIMs. Lanson et al (2015) and Dietel et al (2019b) noticed that some HIM diffraction patterns could be better described as a two-phase system probably caused by segregation effects, which accords with Ferrage et al (2005) who found similar results for pure smectite with different hydration states.…”

“…Dietel et al () presented a 3D crystal structure model of HIS including turbostratic disorder that enables to quantify these phases in a mixture like soil using the Rietveld method. They described HIMs as expandable 2:1 layers randomly interstratified with partly or fully occupied hydroxy‐interlayers, which is in accordance with Lanson et al () and Viennet et al ().…”

“…A Mg 2+ saturated specimen is used in both the air‐dried and glycerol or ethylene‐glycol saturated state to promote interlayer swelling, and a K + saturated specimen typically heated to 350°C and 550°C to promote interlayer collapse, both to estimate the proportion of expandable layers. However, Dietel et al () recently showed that the degree of hydroxy‐interlayering can also be estimated by a combination of XRD and the Rietveld refinement technique, using crystal structure models based on atom coordinates. They showed that the technique allows a reasonable estimate of the degree of hydroxy‐interlayering even when powder samples or preferred‐oriented mounts in air‐dried and ethylene‐glycol saturated state were used without further Mg 2+ /K + exchange, heating, or selective dissolution.…”

“…These conditions differ from the mostly acidic ones in nature (e.g., Gupta and Malik, 1969;Keren et al, 1977;Yamanaka and Brindley, 1978), as the solubility of feldspars and other silicates, as the most important Al 3+ suppliers, is minimized in a neutral to alkaline milieu (Brady and Walther, 1989). However, precipitation of metal hydroxides was often observed during preparation of synthetic HIMs independent of pH (e.g., Yamanaka and Brindley, 1978;Violante et al, 1998;Dietel et al, 2019aDietel et al, , 2019b. For instance, Sakurai and Huang (1998) detected gibbsite around particles of synthetic hydroxy-interlayered montmorillonite in transmission electron micrographs.…”

Quantitative Phase Analysis of Skarn Rocks by the Rietveld Method Using X-ray Powder Diffraction Data

“…Systematic results on the application of Rietveld XRPD quantitative analysis to geological samples have been reported by Hill et al [18] for determination of mineral abundances in a range of igneous, volcanic, and metamorphic rocks, by Mumme et al [19] in sedimentary rocks, and by Mumme et al [20] in massive sulfide ores. The method was successfully applied to various geological materials-montmorillonite rocks [21]; wollastonite skarns [22]; hydrothermally altered rocks [23]; heavy minerals in sandstones [24]; dacitic rocks [25]; pyrite and other sulfide minerals in mine rock piles [26]; bentonites [27]; zeolites and amorphous phases in zeolitized tuffaceous rocks [28]; granitic pegmatite [29]; ultramafic rocks [30]; mineral concentrations in bauxite residues [31]; carbonate rocks containing Mg-rich calcite and non-stoichiometric dolomite [32]; hydroxy-interlayered smectite in soils [33].…”