Three single crystals of sodium zeolite X were fully La3+-exchanged at 90 degrees C from aqueous solution (pH = 7.45, 7.45, and 6.89 at 22 degrees C, respectively). One was vacuum dehydrated at 400 degrees C (crystal 1), another at 22 degrees C (crystal 2), and the third remained fully hydrated (crystal 3). Their structures at 22 degrees C were determined by single-crystal X-ray crystallography in the cubic space groups Fd3m (a = 24.999(3) and 35.059(4) Angstrom) and Fd3 (a = 25.154 (3) Angstrom), respectively. They were refined to the final error indices R-1 = 0.076, 0.091, and 0.078 with 471, 374, and 725 reflections, respectively, for which F-o > 4 sigma(F-o). The number of La3+, H3O+ and OH- ions found in the three structures are about 38, 0, 18; 38, 28, 50; and 33, 16, 24, respectively, per unit cell. Crystal 1 also has 48 nonframework oxide ions and 92 H+ ions per unit cell. In all cases overexchange occurred. In crystal 1, 32 La3+ ions per unit cell fill site I＇, with the remaining six at 12-ring centers (site V). Each of these six coordinates to three OH- ions and three water molecules in a near hexagonal planar manner. A tetrahedron of four La3+ ions at site I＇ is Found in each sodalite unit; each La3+ coordinates to three framework oxygens. This tetrahedron is interpenetrated by a tetrahedron of four oxide ions to give a distorted La4O44+ cube. These cubes are linked by oxide ions at site I to form a neutral La2O3 continuum; a binary intrazeolitic continuum had not been previously reported. In crystal 2, 28 La3+ ions are at site I＇, eight at site V, and two at supercage centers (site IV). Four H3O+ ions are at site I＇, 12 at site III＇, and 12 at site II. In all, 64 water molecules per unit cell coordinate to La3+ ions or bridge between hydrated La3+ ions. Half of the sodalite units contain complete La-4(OH)(4)(8+) "cubes", and the other half contain La-3(OH)(OH2)(3)(8+) units. Two of the eight supercages per unit cell are filled with large clusters. Each consists of a La3+ ion at its center (site IV), four La3+ ions near site V, six H3O+ ions, 19 water molecules, and 15 OH- ions. In crystal 3, eight La3+ ions are at site I＇, 24 at site II, and one at site V. Each sodalite unit contains a La3+ ion at site I＇; this ion coordinates to three framework oxygens and to three OH-ions. Each OH- ion bridges to a La3+ ion at site II, and each triplet of OH- ions is capped by a H3O+ ion. Each supercage contains three La3+ ions at site TT and 19 water molecules. For the first time, the coordination geometries hexagonal planar (crystals and 2) and trigonally monocapped trigonal-prismatic (crystal 3) are seen.