Afghanite

Afghanite, (Na,K)₂₂Ca₁₀[Si₂₄Al₂₄O₉₆](SO₄)₆Cl₆, is a hydrous sodium, calcium, potassium, sulfate, chloride, carbonate alumino-silicate mineral. Afghanite is a feldspathoid of the cancrinite group and typically occurs with sodalite group minerals. It forms blue to colorless, typically massive crystals in the trigonal crystal system. The lowering of the symmetry from typical (for cancrinite group) hexagonal one is due to ordering of Si and Al. It has a Mohs hardness of 5.5 to 6 and a specific gravity of 2.55 to 2.65. It has refractive index values of nω=1.523 and nε=1.529. It has one direction of perfect cleavage and exhibits conchoidal fracture. It fluoresces a bright orange.