Gottardiite has been 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) A. The strongest X-ray diffraction lines are (in A): 11.34 (100), 4.37 (79), 4.01 (57), 3.282(68). The gottardiite framework topology is the same as that of synthetic NU-87. The chemical formula is: Na (sub 2.5) K (sub 0.2) Mg (sub 4.8) Al (sub 18.8) Si (sub 117.2) O 272 93H 2 O. The Si/Al ratio is 6.2 the highest found up to now in a natural zeolite. Gottardiite is optically biaxial (-) with alpha = 1.480(2), beta = 1.485(2), 2V60, where X = b, Y = a and Z = c. The density is 2.14(4) g/cm 3 (obs.), and 2.16 g/cm 3 (calc.). Both thermal stability and rehydration capacity are very high. The name is in honour of Glauco Gottardi (1928-1988).