The concept of an aristotype, or equivalently, the basic structure, that represents the highest symmetry crystal structure that can be attained, either experimentally, or theoretically, from a lower symmetry phase, has had a long standing in structural crystallography from its earliest days. Crystallographic evolution from a lower symmetry phase (the hettotype) to the aristotype is well established for aristotype phases in which the constituent atoms all lie on special positions with no crystallographic degrees of freedom. For more complex crystal structures the definition of the aristotype is moot. We have recently defined an aristotype crystal structure for leucite-structured phases as the phase with an ideal SiO4 tetrahedron. In this POLARIS experiment, we propose to study the temperature dependence of K2MgSi5O12 leucite to determine if this is a correct deduction.