Abstract <p>For the first time, loparite-(Ce) has been found in a xenolith of phoscorite from the calcite carbonatite of the Guli complex of the Maimecha-Kotui alkaline province (Krasnoyarsk Krai, Russia). Its composition is close to the end member (Na_0.5<i>LREE</i>_0.5)TiO₃. Crystals of loparite-(Ce) occur in magnetite as relict inclusions, their intermediate and marginal zones are characterized by a zonal distribution of rare earth elements (REEs). Local areas enriched in Nb and Th are recorded in the marginal zones. Compositional variations of the mineral are described by the following isomorphism schemes: Ca²⁺ + Ti⁴⁺ ↔ Na⁺ + (Nb + Ta)⁵⁺ and REE³⁺ + Ti⁴⁺ ↔ Ca²⁺ + (Nb + Ta)⁵⁺. Based on the results of Raman spectroscopy, areas differing in structure and chemical composition of REEs are identified in loparite crystals. It is concluded that isomorphism affects the distortion of the crystal structure and the transformation of vibrational modes. The obtained results indicate that loparite-(Ce) was formed at the early stages of crystallization of a melt consisting of two alkaline-carbonatite immiscible liquids and the later crystallization of pyrochlore and zirconolite is consistent with the fact that the residual carbonatite melt was enriched in fluorine, rare earth and radioactive elements.</p>