New Data on the Isomorphism in Eudialyte-Group Minerals: XIII. Crystal Structure of “Ferrofeklichevite”—a Potentially New High-Calcium Mineral from Khibiny Massif

The crystal structure of a high-calcium eudialyte-group mineral from alkaline rocks of the Khibiny massif has been studied. The trigonal unit cell parameters are a = 14.221(1) Å, c = 30.04(1) Å, V = 5261.3(4) Å3, sp. gr. R3m. The crystal structure has been refined to a final R = 2.8% in the isotropic approximation of atomic displacement parameters, using 1714 reflections with F > 3σ(F). The studied mineral is similar in chemical composition to feklichevite, but differs from it in the predominance of divalent iron, as well as in a lower calcium content and a higher manganese content. The structural features of calcium-rich eudialyte-group members from three alkaline massifs are discussed.