Pedogenesis of Two Forest Soils (Kandiustults) Derived from Metamorphosed Granite in Korea

Abstract Soils derived from granite rocks occupy 66% of the land in Korea. Two soils from the southern part of Korea formed on metamorphosed granite under forest vegetation, containing high amounts of ferruginous chlorite, were studied to evaluate weathering and formation of clay minerals. The soils are deeply weathered, strongly acid, low in organic matter and cation‐exchange capacity (CEC), and the amounts of clay in the very thick Bt horizons are almost three times higher than in the BC horizons. Micromorphology of the thin O horizon showed common characteristics of moder humus and evidence of high biological activity. High contents of coarse grains and low plasma impart to the E horizon an enaulic‐related distribution pattern. The most striking micromorphological features are multilaminated, generally limpid ferriargillans in the Bt and BC horizons. While some chlorites are intact or partly weathered in the E and BC horizons, they are entirely weathered in the Bt horizons. High clay contents in the Bt horizons are not only due to clay translocation, but also to intensive in situ mineral weathering in this zone. The most significant pedogenic processes, as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were formation of Fe oxyhydroxide and tubular halloysite from the weathering of chlorite and other primary minerals. Iron oxides imparted a typical red color to the soils. Total chemical analysis of clays revealed extensive loss of Ca, K, and Na and concentration of Fe and Al. Almost equal proportions of Al and Si oxides support a clay fraction dominated by halloysite and kaolinite. Mineralogical studies of clays in the Bt horizon showed that, while feldspars were partly weathered, chlorite, under a well‐drained, acid, humid temperate to semitropical environment, was completely weathered to kaolinite, halloysite, hematite, goethite, gibbsite, and a chlorite‐vermiculite intergrade, probably hydroxy‐interlayered vermiculite (HIV). Some dioctahedral mica appeared to be resistant in the soils.