Imogolite: a unique aluminosilicate

Abstract

The fibrous aluminosilicate imogolite has been studied by electronoptical and infrared absorption methods. Electron diffraction patterns are interpreted in terms of repeat units of 8·4 Å parallel and 23 Å perpendicular to the fibre axis. These spacings can not be reconciled with a continuous silicate chain structure and this conclusion is supported by an Si-O vibration near 930 cm⁻¹. A structure is postulated in which distorted chains of Al-O octahedra are cross-linked through isolated Si₂O₇ groups.Multiple OH stretching vibrations indicate different types of OH group in the imogolite structure. Absorption bands near 1000, 700 and 600 cm⁻¹ are sensitive to sample orientation. This is attributed to the morphology and dimensions of the imogolite fibres.