Computer graphics representation of the structure of the zeolite VPI5 (Virginia Polytechnic Institute), a framework structured solid. VPI5 has large unidirectional pores that can admit large organic molecules. The framework of this substance is constructed from sub-units of aluminium phosphate. Atoms of phosphorus & aluminium are coloured yellow, with oxygen in blue. The channels & interconnecting cavities formed by the structures of zeolites present an ideal environment for shape-selective catalysis. A number of industrial processes use zeolite catalysts, notably in the cracking of petroleum.