Weathering of glauconite in soils of temperate climate as exemplified by a Luvisol profile from Góra Puławska, Poland

•Glauconite weathering in a Luvisol developed in moderate climate was studied.•The weathering causes glauconite smectitization and likely formation of kaolinite.•Glauconite smectitization involves selective leaching of octahedral Mg and Fe.

The aim of the research reported herein was to study the weathering of glauconite taking place in a Luvisol profile developed on quartz-glauconitic sand in Góra Puławska (eastern Poland) using X-ray diffractometry, Fourier transform infrared spectroscopy, Mossbauer spectroscopy, SEM–EDS, and an optical microscope. The bulk soil material contains quartz, glauconite, glauconite–smectite mixed-layered minerals rich in smectite layers, and traces of feldspars. When compared with the parent material (the Cg horizon), the Bt1 and Bt2 horizons are enriched in clay minerals while the Ap, AEg, and E horizons are depleted in clays. The observed mineral distribution is most likely controlled by the weathering of clay minerals in the uppermost part of the profile and translocation of clay fractions down the profile (lessivage). However contamination with glaciofluvial and/or aeolian material has to be taken into consideration. According to the microscopic observations of the thin sections clay is present in the BCg and Cg horizons in the form of clay coatings and clay infilings. This indicates that initially the parent sand did not contain clay fraction. The fraction was formed most likely in the upper part of the soil profile and was deposited in the lower horizons by percolating atmospheric water. Green pellets separated from all the soil horizons are composed of glauconite showing more or less uniform chemical composition, while clay fractions from all the horizons contain glauconite and glauconite–smectite. Fine clay fractions separated from Ap and AEg horizons are enriched in glauconite–smectite relative to the fractions separated from the lower horizons. The presence of glauconite and glauconite–smectite minerals in the clay fractions studied indicates that glauconite weathering in the soil studied involves formation of glauconite clay by the pellet disintegration and glauconite smectitization. Ferrous iron accounts only for < 0.1 layer charge per half unit cell in the primary glauconite. This indicates that ferrous iron oxidation is not the main mechanism leading to the glauconite smectitization. Because the glauconite–smectite appears to be depleted in magnesium and total iron and enriched in aluminum and silicon relative to primary glauconite, leaching of magnesium and iron together with possible reorganization of the structure appears to be the likely mechanism for the glauconite smectitization.