Rectorite as a Syngenetic Component of a Soddy-Podzolic Soil

Abstract

Rectorite (allevardite) is a regularly interstratified mica–smectite, in which each mica (A) layer is “sandwiched” between smectite (B) layers creating ABABAB…. sequence with 50% contribution of each layer. Similar to other ordered minerals, rectorite is rare in nature. The paper provides the results of the study on properties and mineral composition of the soddy weakly podzolic soil (Umbric Albeluvisol) in the Komi Republic, Russian Federation. Rectorite is found in fine fractions of A1 and A2 horizons of this soil. The studied soil has been formed on the light-textured parent material. The soil profile is texturally differentiated by the eluvial type. In the mineral horizons, $${\text{p}}{{{\text{H}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ varies within 5.1–5.3. The mineral composition of fractions <2, 2.0-0.5 and <0.5 μm was studied by X-ray diffractometry (XRD). In the parent material, smectite predominates and is represented by the high-charged beidellite. In addition, its clay fraction contains mica, vermiculite, kaolinite and chlorite, as well as fine quartz. Vermiculite structure is chloritized. The mineral composition of the clay fraction undergoes transformation within the upper 40 cm of the profile, which is maximally pronounced in the upper 20 cm. The content of smectite is lower there; and that of fine quartz is higher, fine fractions additionally contain rectorite. This mineral is identified on the base of the integer (00h) reflection series 24.54 and 12.27 A for air-dry samples. After saturation with ethylene glycol, the (001) peak shifts to 26.77 A. Calcination during 2 h at 550°C results in shifting of this peak to 10 A. Rectorite is believed to be a syngenetic component of this soils and is formed at the early stage of smectite transformation into illite, being a transitional product of this transformation.