TERRANOVAITE FROM ANTARCTICA - A NEW PENTASIL ZEOLITE

A new high-silica zeolite, terranovaite, was recently found in cavitie s of Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarcti ca). The mineral [(Na4.2K0.2Mg0.2Ca3.7)(Sigma 8.3)(Al12.3Si67.7 )(Sigm a 80.0)O-160. >29H(2)O] occurs as globular masses that flake off in tr ansparent lamellae; it has a vitreous luster, white streak, {010} perf ect cleavage, and {001} distinct parting. The observed density is 2.13 +/-0.02 g/cm(3). Optically, it is biaxial positive, with 2V=65 degrees , alpha=1.476, beta=1.478, gamma=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) Angstrom and topological symmetry Cmcm. The str ongest powder X-ray diffraction lines are (d (Angstrom), I, hkl): 11.9 4,40,020; 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 synthet ic zeolites, is characterized by the presence of pentasil chains and o f a two-dimensional ten-membered ring channel system. The mineral was named terranovaite after the Italian Antarctic Station at Terranova Ba y, Antarctica.