Development of Halloysite/Smectite Mixed Layer Mineral in Paleudult of Java Island

This study was initiated to investigate the development of unique kaolin/smectite mixed layer minerals in the Paleudult of Java Island. The present study was aimed to identify the kaolin minerals and to understand the development of the kaolin/smectite mixed layer. Clay fraction samples were collected from the Paleudult profile. Selective dissolutions using dithionite citrate bicarbonate, NaOH, and Na-citrate treatments were conducted on the clay fraction. The result showed that free iron oxide content increased with the depth. Halloysite which showed a 7.6 A peak on the X-ray diffraction (XRD) was confirmed by the hot NaOH extraction. SiO2/Al2O3 molar ratio from the hot-citrate extracts provided the halloysitic property only in the upper horizons. However, the peaks of 10-14 A on the XRD collapse at 300 C following the hot citrate treatment suggesting that crystallinity of the halloysite mineral is weak. This halloysite mineral developed well in the upper horizons. The development of halloysite/smectite mixed layer is proposed in the four stages. Key Words: Halloysite, development of halloysite/smectite mixed layer.