A Kaolin-smectite interstratification sequence from a red and black complex

Abstract

The sequential development of kaolin by progressive alteration of smectite, involving kaolin-smectite interstratifications as a genetic link is described from a red and black complex. Mineral compositions were studied using XRD, DTA and XRF techniques. The basaltderived soils are situated along a 600 m transect and grade in colour from dark grey (10 YR 3/1 ) to red (5 YR 3/3). The kaolin proportions in the interstratification increase almost linearly with increasing reddening up to ~80%. Whole-soil chemical analyses exhibit no significant variations in the major element composition, but dithionite extractable Fe increases along the transect from 1% to 4-16%. Hematite and goethite are the only secondary iron phases. Topographic differences are slight but sub-surface bedrock contours plus appreciable variations in sand content between red and black soils could be genetically significant.

Clay Mineralogy of Basaltic Hillsides Soils in the Western State of Santa Catarina

“…In the Mg sample, a weak reflection at d ≈ 0.991 nm was also observed, indicating micas or illites, as well as another more intense reflection at d values between 1.30 and 1.40 nm, increasing to d values ≈ 1.725 nm in the treatment with ethylene glycol, confirming the expansive character of this mineral. When smectite peaks do not follow a rational series (absence of reflection 003, at d =5.00 nm, for example), and when the glycolation treatment promotes shifting of the reflections to values above 1.70 nm, as observed, this indicates the presence of interstratified K-S (Bühmann and Grubb, 1991;Righi et al, 1999). This higher content of smectite and interstratified kaolinite-smectite explains, therefore, the high CEC and clay activity values of this soil (Table 3).…”

“…In profile 5 (horizon A), the reflections with larger area and expression occur at d values around 0.72 and 0.36 nm (Figure 3), but they are broad and asymmetrical, possibly indicating kaolinite in association with interstratified kaolinite-smectite, as evidenced by several authors analyzing younger basalt-derived soils (Bühmann and Grubb, 1991;Vingiani et al, 2004;Teske et al, 2013). The presence of goethite is indicated by the reflection at 0.417 nm.…”

“…The reflections at d ≈ 0.722 nm have a strong asymmetry at lower 2θ angles, albeit to a lesser degree than in the previous profiles. Since there was no change in the position of the reflections in this region due to heating or glycolation treatments, this behavior indicates that the interstratified K-S have hydroxyl-Al polymers in the interlayer spaces, as described by Bühmann and Grubb (1991). Considering these results, the presence of SIHP, together with K-S interstratified with hydroxyl-Al polymers, although occurring in significant quantities, probably contribute little to the increase of CEC in this soil (clay fraction activity in the B2 horizon 14.04 cmol c kg -1 ), i.e., compatible with the observed mineralogy.…”

“…When the three diffractograms are inserted simultaneously for comparison (Figure 5d), the differences in the reflection pattern of the supposed kaolinite appear with greater clarity. This pattern, although already mentioned as indicating the presence of interstratified K-S in many environments, in particular in basalt-derived soils (Bühmann and Grubb, 1991;Vingiani et al, 2004), is often ignored during interpretation, and will require more attention in the future.…”

“…These characteristics indicate the presence of interstratified minerals, possibly kaolinite-smectite (K-S) type, associated or not with kaolinites, according to Środoń (2006) and Ryan and Huertas (2009). However, ethylene glycol impregnation, and/or heat treatments generally used to identify their presence (Ryan and Huertas, 2009) induced no modification in the reflection patterns at this position, indicating that the interlayer space of the expandable portion of the interstratification may be blocked with hydroxy-Al polymers (Delvaux et al, 1990;Bühmann and Grubb, 1991). Thus, with the XRD tools alone, the type and proportion at which these interstratified minerals occur in the soil samples could not be identified.…”