The effect of weathering in the silt fractions on the apparent stability of chlorite in Scottish soil clays

Abstract

Previous work on chloritic soils in Scotland indicated that, irrespective of soil type or drainage class, the chlorite that was dominant in the clay fractions weathered only slightly, showing little variation in amount with depth. These soils have been investigated further by determination of the chlorite content in the silt fractions by a quantitative X-ray diffraction technique. In a Dystric Cambisol and a Placic Podzol, the fine silt fractions (1.4–20 μm) contain much more chlorite than the coarse silt (20–75 μm) and in both fractions the amount of chlorite decreases towards the surface, markedly so in the Placic Podzol. It is suggested that chlorite is being dissolved out from the clay fractions but as chlorite is being broken down and transferred to finer particle size fractions, this dissolution effect is being masked by the replacement of the clay fraction chlorite from the fine silt. Analysis of the total soils (<22 mm) confirmed the net loss of chlorite from these profiles.