POLYSOMATIC ASPECTS OF MICROPOROUS MINERALS - HETEROPHYLLOSILICATES, PALYSEPIOLES AND RHODESITE-RELATED STRUCTURES

Abstract

Several structural families reported in this book can be described by using concepts of modular crystallography (Thompson 1978; Veblen 1991; Merlino 1997; Ferraris et al. 2004). This chapter presents three groups of microporous minerals emphasizing the modular aspects of their crystal structures and the role that modularity plays in correlating different structures as well as structure and properties, namely aspects aimed at an engineering of microporous materials (cf. Rocha and Lin 2005). The description of a crystal structure as an edifice consisting of complex building modules that occur also in other structures implicitly leads to identify features that are common to a group of compounds. This kind of group can often be expressed as a series of structures that are collinear in composition and cell parameters, information that may be crucial to model unknown structures related to the series, as illustrated by some examples in this chapter. Biopyriboles (Fig. 1⇓) represent a first and now classical example of modular structures established by Thompson (1978). He showed that the structures of micas, pyroxenes and amphiboles share, according to different ratios, the same modules of mica ( M ) and pyroxene ( P ) and are members of a polysomatic series MmPp . The ideal chemical composition and cell parameters of the members of the series are linear functions of the ratio m / p . The classification of biopyriboles as members of a polysomatic series, a type of series belonging to the wider category of the homologous series (cf. Ferraris et al. 2004), and the consequent discovery of the multiple-chain-width biopyriboles jimthompsonite and chesterite (Veblen and Buseck 1979) dramatically proved the predictive power of these series in terms of structure characterization and modeling. The modeling of carlosturanite (Mellini et al. 1985) and of other modular structures …