1 Heterophyllosilicates: prospects of technological applications Giovanni Ferraris Dipartimento di Scienze Mineralogiche e Petrologiche, Università di Torino – Istituto di Geoscienze e Georisorse, CNR – Via Valperga Caluso 35, I-10125 Torino, Italy giovanni.ferraris@unito.it This paper is dedicated to Academician Professor Nikolai Yushkin in occasion of his 70th Anniversary. Abstract - Heterophyllosilicates are titanosilicates based on layers which can be formally derived from the tetrahedral-octahedral-tetrahedral (TOT) layer of phyllosilicates by periodic substitution of rows of Si-tetrahedra by rows of Ti-polyhedra. According to the periodicity of the substitution, three types of HOH layers (H to indicate the hetero substitution) are known: bafertisite-, astrophyllite- and nafertisite-like. The phyllosilicates are the starting natural material that is used to prepare an increasing number of compounds where TOT layers and organic molecules are intercalated to form organoclays, pillared clays and nanocomposites. These classes of materials are widely used for their properties (e.g., pollutants absorbers, catalysers and molecular sieves). Following structural (layers) and physical-chemical (swelling) analogies between the two classes of compounds, it is proposed that some heterophyllosilicates based on bafertisite-like layers could in principle be used to produce materials analogous to those mentioned above for phyllosilicates. Problems along this route are the poor availability of heterophyllosilicates, which are rare minerals, and, consequently, the necessity of synthesising them, a step not yet well established.