X-ray studies of halloysite and metahalloysite

Metahalloysite is one of the kaolin group of minerals with a composition approximating to the formuia Al 2 O 3 .2SiO 2 .2H 2 O, and its structure is generally considered to be built of composite layers of atoms of the kind found in other minerals of this group. It differs from them most strikingly in that it can be produced by the dehydration of the hydrated mineral halloysite, which has the approximate composition Al 2 O 3 .2SiO 2 .4H 2 O. Both minerals give comparatively poor X-ray diagranm showing relatively few lines attd bands. The lines correspond to reflections from a basal spacing of about 7·2 Å. in metahalloysite and 10·1 Å. in halloysite.