The expression ‘Modular Analysis’ (MA) refers to objects which are amenable to general considerations and definite conclusions in terms of some modules constituting the objects. The modular analysis of crystal structures (henceforth MACSs) includes the following aspects: modular interpretation, description, relationships in sets of CSs having common modular features, analytical means for consideration and operations with MSs revealing their independence or equivalence, lattice, symmetry and diffractional scattering power, derivation-identification of real and derivation-prediction of hypothetical MSs, simulation of MS models and calculation of diffractional characteristics.
The modular aspect of crystal structures provides a clear description more expressive than formal tables of atomic coordinates. It presents separate CSs not as isolated objects but in their relationships to other CSs which have some common modular features. The symmetries of MSs combine features of the single modules and of their spatial arrangement. Symmetry here is not only a characteristic feature but serves also as an explanation for the origin and existence of the MS diversities. For this latter aspect there is a problem of definitions and nomenclature which should help to get an adequate understanding of the nature of matter, avoiding ambiguity, unnecessary complications and confusions. The requirement of usefulness should be the main criterium in the use of different terms. It is desirable to have terms belonging to the common language and of general use, which directly express their sense without resorting to unusual and exotic terminologies. The nomenclature may concern modular series and sets depending on the module combinations
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Modular Aspects of Minerals
Since the first beginning of the crystal chemical study of the inorganic compounds, a simple modular approach was developed, by looking at the crystal structures as built up through the assembling of simple polyhedral units. This approach was no only useful for a vivid and insightful description of the complex atomic arrangements of natural and synthetic compounds, but, through the use of simple and powerful rules for assembling polyhedral units, it displayed an extraordinary heuristic power, suggesting reliable models for many complex structural assemblages. The polyhedral approach also laid the basis for meaningful classifications which were applied to all the classes of inorganic compounds.