A new high-silica zeolite, terranovaite, was recently found in cavities of Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica). The mineral [(Na4.2K0.2Mg0.2Ca3.7)Σ8.3 (Al12.3Si67.7)Σ80.0O160 · > 29 H2O] occurs as globular masses that flake off in transparent lamellae; it has a vitreous luster, white streak, {010} perfect cleavage, and {001} distinct parting. The observed density is 2.13 ± 0.02 g/cm3. Optically, it is biaxial positive, with 2V = 65°, α = 1.476, β = 1.478, γ = 1.483 (all ± 0.002). The orientation is X = c, Y = a, and Z = b. Terranovaite is orthorhombic with a = 9.747(1), b = 23.880(2), c = 20.068(2) Å and topological symmetry Cmcm. The strongest powder X-ray diffraction lines are (d (Å), I, hkl): 11.94,40,020; 10.16,65,021,002; 9.04,33,110; 3.79,100,025,240; 3.61,40,153. Terranovaite topology, hitherto unknown in either natural or synthetic zeolites, is characterized by the presence of pentasil chains and of a two-dimensional ten-membered ring channel system. The mineral was named terranovaite after the Italian Antarctic Station at Terranova Bay, Antarctica.

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