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Crystal chemistry connects a crystalline material's composition, chemical bonds and atomic arrangement. It asks which coordination numbers, local geometries and substitutions are compatible with an observed crystal structure.

For example, the usual sodium chloride structure gives each ion six nearest oppositely charged neighbours, whereas the usual caesium chloride structure has eight. Charge balance constrains composition, while size, bonding and thermodynamic conditions influence which arrangement is stable. Ionic-size rules are useful guides rather than exact universal predictions. X-ray diffraction tests the arrangement experimentally, allowing composition-based expectations to be compared with measured periodic atomic structure.

Victor Goldschmidt, the geochemist Victor Moritz Goldschmidt, related the distribution of chemical elements to their chemical behaviour and the properties of minerals. His work on atomic radius values and ionic radius values connected crystal chemistry with crystallography; his geochemical classification organized elements according to their association with different material reservoirs.^[ref]