Zn vapor at 480°C reduced all Cd 2+ ions, and some Si 4+ ions, in a single crystal of fully dehydrated fully Cd 2+ -exchanged zeolite X (Cd 46 Si 100 Al 92 O 384 per unit cell). The product crystal has the approximate unit-cell composition Zn 64 Si 96 Al 96 O 384 ‚7SiO 4 4-,1AlO 4 5-(a 0 ) 24.713(3) Å). The other products, Cd(g) and Si(s), left the crystal. Its structure was determined by X-ray diffraction in the cubic space group Fd3 h. Of the approximately 64 Zn 2+ ions per unit cell, 57 are in the sodalite units (28 at site I′, 23 at site II′, and six on 2-fold axes opposite four-rings), and seven are at site II in the supercage. Seven orthosilicate ions and one orthoaluminate ion fill the eight sodalite units per unit cell. Some units of zeolite framework structure must have "dissolved" to provide these ions; the remaining framework structure must be enriched in aluminum, and cavern formation is proposed. Most orthosilicate oxygen atoms bridge between a Zn 2+ ion at site I′ (1.91 Å) and another at site II′ (2.08 Å) and lie in its Zn 2+ , Zn 2+ , Si 4+ plane; each of these Zn 2+ ions coordinates tetrahedrally to three framework and one orthosilicate oxygen atom. Each orthoaluminate ion coordinates symmetrically to six Zn 2+ ions which lie on 2-fold axes; each of these Zn 2+ ions coordinates tetrahedrally to two framework and two orthoaluminate oxygen atoms.