Zirconium Silicates

a group of rare minerals, the basic structural elements of which are complex silicon-zirconium radicals of the following type: [Zr(Si₃O₉)]^2– (the catapleiite sub group), [Zr(Si₄O₁₁)]^2– (the vlasovite subgroup), [Zr(Si₆O₁₅)]^2–(elpidite), {Zr [Si₆O₁₂(OH)₆]}^2– (lovozerite), and {Zr₃ [Si₃O₉] · [Si₉O₂₄(OH)₃]}^9– (eudialyte). Na⁺, K⁺, Ca²⁺, Cr²⁺, Ba²⁺, and IR³⁺ serve as the cations in zirconium silicates. There are about 30 known zirconium silicates, for which framework and ring crystal structures are characteristic. The hardness of these minerals on Mohs’ scale is 4–5, and the densities range from 2,600 to 3,200 kg/m³. Zirconium silicates crystallize from highly alkaline melts and solutions. They are characteristic of nepheline syenites, syenite-pegmatites, and alkaline metasomatic zones, where they are associated with nepheline, natrolite, microcline, albite, aegirine (or aegirite), and other minerals.