View article

Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. When both halloysite and kaolinite are present in a given sample, differentiation between the two minerals is problematic particularly when the halloysite constituent is dehydrated. Formamide intercalation test is widely used to differentiate halloysite-(7 Å) from kaolinite. The soil used in this study was taken from an Udalf B horizon. It was sampled in 1986, immediately studied, and then stored. This soil was selected due to its high halloysite-(10 Å) content. The formamide intercalation test was performed on 3 clay fractions (<0.1, 0.1–1, and 1–2 μm) re-extracted from the stored soil. X-ray diffraction shows that the hydrated halloysite, initially present (in the fresh sample), is totally dehydrated after storage. Since the interlayer water in halloysite is weakly held, halloysite-(10 Å) can …