Laboratory analyses of sulpho-rendzinas

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		Specific structural features of Sulpho-rendzinas: Gypsum powder i.e. gypsum fine earth consisting of sand-sized residual fragments of microcrystalline gyprock and silt-sized individual crystals. We have established that it is formed by cryogenic disintegration combined with dissolution of gyprock. Gypsum coatings or pendants on lower faces of gyprock fragments. Apparently, they crystallize from saturated calcium-sulphate solutions that are capillary suspended on the lower faces of gyprock fragments. Gypsum powder under polarizing microscope Gypsum coating or pendant: macro-image (left) and under electronic microscope (right) The bulk chemical composition the mineral horizons corresponds to very pure gypsum (CaSO4 x 2H2O). The brown-ocher hues of gypsum powder just under the O horizon and those of gypsum coatings are due to the presence of micro-quantities of organic substances and iron oxides. The X-ray diffraction patterns confirmed that all structural elements of the mineral matter are gypsum with only insignificant admixtures of anhydrite, quartz and calcareous minerals. This pure gypsum is extremely poor in P, K and other plant nutrients, except Ca and S. The organic horizons are acid and weakly acid; the mineral horizons are from acid to neutral and are humus-poor. The values of pH in KCl are often higher than pH in H2O, which is known as geric property (WRB, 2006) and explained by the very low cation exchange capacity of gypsum. Click to go to: *study sites* - *findings* - *world occurrence*
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