What is "voronkovite"

Voronkovite is a very rare mineral of the eudialyte group with the formula Na(Na,Ca,Ce)(Mn,Ca)FeZrSiSiO(OH,O)Cl·HO. The formula is based on the simplified original one; it does not show the presence of cyclic silicate groups, but two M3- and M4-site silicon atoms are shown separately (basing on the nomenclature of the eudialyte group). Voronkovite has lowered symmetry (space group R3, instead of more specific for the group R3m one), similarly to some other eudialyte-group members: aqualite, labyrinthite, oneillite and raslakite. The specific feature of voronkovite is, among others, strong enrichment in sodium.