Frankamenite
Frankamenite is the fluorine-dominate variation of the rare mineral canasite with a general formula of K3Na3Ca5(Si12O30)[F,(OH)]4·(H2O).
Frankamenite belongs to the triclinic crystal system, with the bases of its structure containing Ca-Na mixed octahedra joined by octagonal tubes SiO4 of the composition (Si12O30). Frankamenite has six Ca-Na mixed positions distributed amongst these octahedra, reflecting its varying compositions.