Khomyakovite

Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula Na₁₂Sr₃Ca₆Fe₃Zr₃WSi(Si₉O₂₇)₂(Si₃O₉)₂O(O,OH,H₂O)₃(OH,Cl)₂. The original formula was extended to show the presence of both the cyclic silicate groups and M4-site silicon, according to the nomenclature of the eudialyte group. Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common. The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display stronium diadochy. Khomyakovite is the third eudialyte-group mineral with essential tungsten (after johnsenite-(Ce) and manganokhomyakovite).