The crystal structure of a low-calcium representative of the eudialyte group from Lovozero (Kola Peninsula) was studied by single-crystal X-ray structural analysis in the framework of the P3 group, 165 positions, R = 5.4%, 4469 reflections with F > 2σ(F). The mineral with the idealized formula Na15(Ca3Mn3)Zr3(Fe,Zr)3(Si,Ti)(Si,Nb)Si3O92Si9O272O2(OH,F,Cl)2·2H2O is a Sr-containing analogue of oneillite with a low niobium content and a predominance of silicon both in the M3 and M4 positions. The unit-cell parameters are a = 14.192(2) Å, c = 30.170(5) Å, V = 5262.74 Å3. Within the P3 model, in addition to the oneillite-type ring Ca–Mn, the eudialyte ring Ca–Ca and the ring of the composition Na–(Ca,Sr) are also established. The crystallochemical role of strontium in minerals of the eudialyte group is analyzed.
Rastsvetaeva et al. (2026) studied this question.