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We introduce and discuss an interpretative model of the structure and bonding of inorganic crystals containing metallic elements. The central idea is the conception of the crystal structure of such an inorganic compound as a metallic matrix whose geometric and electronic structures govern the formation and localization of the anions in the lattice. This is the reason for labelling the model anions in metallic matrices (AMM). Taking the Al X3 crystal family ( X = F, Cl, OH) as a suitable test-bed class of compounds, we illustrate how this approach gives a direct interpretation of the crystalline structures and explains the variable coordination that Al exhibits in crystalline materials. An exhaustive analysis of the topology of the electron density allows us to provide a quantum-mechanical assessment of the main hypotheses of the AMM model and to uncover, using microscopic arguments, the behavior of anions as chemical pressure agents. [ABSTRACT FROM AUTHOR]