Gottardiite, a new high-silica zeolite from Antarctica: the natural counterpart of synthetic NU-87

Gottardiite was discovered in the Jurassic Ferrar dolerites of Mt. Adamson (Northern Victoria Land, Antarctica). The new zeolite occurs as subparallel aggregates of transparent pseudo-hexagonal lamellae. The mineral is orthorhombic, space group Cmca, with a=13.698(2), b=25.213(3), and c=22.660(2) Å. The strongest x-ray diffraction lines are (in Å): 11.34(100), 4.37(79), 4.01(57), 3.282(68). The Gottardiite framework topol. is the same as that of synthetic NU-87. The chem. formula is: Na2.5K0.2Mg3.1Ca4.8Al18.8Si117.2O272.93H2O. The Si/Al ratio is 6.2, the highest found up to now in a natural zeolite. Gottardiite is optically biaxial (-), with α=1.480(2), β=1.485(2), γ=1.486(2), 2V<60°, where X=b, Y=a and Z=c. The d. is 2.14(4) g/cm3 (obs.), and 2.16 g/cm3 (calc.). Both thermal stability and rehydration capacity are very high. The name is in honor of Glauco Gottardi (1928-1988).