Abstract
Calcitic plasmic fabric, grain calcans, neocalcitans and carbonatic glaebules with diffuse boundary were studied in situ, in soils by electron probe and SEM analyses. The occurrence of pedogenic magnesium-bearing calcite, previously detected by a shift of X-ray diffraction spacing on bulk samples, was verified by electron probes analyses on purely pedogenic carbonatic sites. This made it possible to understand further the nature of carbonates and to differentiate pure calcite from magnesium-bearing calcite. Common types of microcrystalline pedogenic carbonates included elongated, equidimensional, rod-shaped, and layered crystals. Equidimensional crystals were common in calcite, whereas elongated and rod types occurring sometimes as bundles of coalescing fibres were found to be magnesium calcite. Most visible pedogenic carbonate crystals in the soils studies had a diameter of 0.3–1.0 μm. This size range may be important in establishing relative levels of secondary carbonates in soils. Phosphorus values for studied features were higher than in the entire soil and arc evidence of precipitation of this element with pedogenic carbonates.
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