The prominent (Si O2) 8 O2 H3- mass peak resulting from the laser ablation of hydroxylated silica, attributed to magic cluster formation, is investigated employing global optimization with a dedicated interatomic potential and density functional calculations. The low-energy spectra of cluster isomers are calculated for the closed shell clusters: (Si O2) 8 O H- and (Si O2) 8 O2 H3- giving the likely global minima in each case. Based upon our calculated cluster structures and energetics, and further on the known experimental details, it is proposed that the abundant formation of (Si O2) 8 O2 H3- clusters is largely dependent on the high stability of the (Si O2) 8 O H- ground state cluster. Both the (Si O2) 8 O2 H3- and (Si O2) 8 O H- ground state clusters are found to exhibit cagelike structures with the latter containing a particularly unusual tetrahedrally four-coordinated oxygen center not observed before in either bulk silica or silica clusters. The bare ground state (Si O2) 8 O2- cluster ion core is also found to have four tetrahedrally symmetric SiO terminations making it a possible candidate, when combined with suitable cations, for extended cluster-based structures/materials.