Two crystal structures of fully dehydrated, fully Ag+-exchanged zeolite X have been determined by single-crystal X-ray diffraction techniques. Ion exchange was accomplished by allowing 0.05 M aqueous AgNO3 to flow past each crystal for 3 days to give hydrated Ag92Si100O384. One crystal was dehydrated at 400 degreesC for 2 days, followed by cooling to 21 degreesC, all in a flowing stream of dry oxygen gas (790 Tort), followed by evacuation at 2 x 10(-6) Torr for 20 min. The structure was determined in the cubic space group Fd (3) over barm (a = 25.177(4) Angstrom) and was refined to the final error indices R-1 = 0.048 and R-2 = 0.078 with 291 reflections for which I > 3sigma(I). The second crystal (a = 24.871(4) Angstrom) was similarly dehydrated without oxygen. Its structure was determined in Fd (3) over bar and refined to R-1 = 0.069 and R-2 = 0.072 with 320 reflections as above. In the first crystal, 4 Ag+ ions were found at the octahedral site I (Ag+-O = 2.689(7) Angstrom) and 24 Ag+ ions occupy the nearby site I' positions (Ag+-O = 2.220(10) Angstrom), avoiding I-I' contacts. Thirty-two Ag+ ions fill site II (Ag+-O = 2.360(10) Angstrom), and the remaining 32 Ag+ ions occupy a III' site (Ag+-O = 2.368(12) and 2.586(15) Angstrom). No reduction of Ag+ has occurred. In the second crystal, 16 Ag+ ions fill site I (Ag+-O = 2.573(10) Angstrom), 32 partially reduced Ag+ ions half fill two different site I' positions that are unusually deep in the sodalite cavities (Ag-O = 2.628(10) and 2.708(14) Angstrom), and 16 Ag+ ions half fill the 32-fold site II' inside the socialite cavity (Ag+-O = 2.461 (11) Angstrom). Sixteen Ag+ ions half fill the 32-fold site II (Ag+-O = 2.231(11) Angstrom), and eight Ag+ ions lie at two different III' sites. In total, only about 86 silver atoms or ions were found per unit cell of crystal 2. The remaining six have migrated out of the zeolite framework to form small silver crystallites on the surface of the zeolite single crystal. In this structure, each sodalite cavity hosts a cationic silver cluster. In half, eight silver atoms form interpenetrating tetrahedra, Ag-8(n+), with T-d symmetry. The other half host cyclo-Ag-4(m+) cations with near S-4 symmetry. Likely values of n and m are 4 and 2, respectively.