Rings containing four tetrahedrally coordinated atoms connected by bridging O atoms in a single four ring (S4R) geometry have been used to model the properties of ring species occurring in aluminosilicate and borosilicate crystals, glasses, and melts. We recently established a molecular basis for the Al avoidance, or Loewenstein's rule, using molecular quantum mechanical methods applied to the non-Loewenstein paired, i.e., Al Al Si Si , and the Loewenstein alternating, i.e., Al Si Al Si , geometric isomers of the Si 2 Al 2 O 4 H - 2 8 molecular anion. We here extend this model to the Si 2 Al 2 O 4 H - 2 8 and Si 2 B 2 O 4 H - 2 8 molecules neutralized by various counterions such as H + , CH + 3 , Na + , and Ca 2 + . Our calculations show that the paired geometry isomer can be strongly stabilized by coordination of counterions to the underbonded bridging O in the Al-O-Al or B-O-B linkages. For the Si 2 Al 2 case, coordination of H + or Ca 2 + to the underbonded O actually makes the paired geometry isomer more stable than the alternating geometry one. This result helps us to explain why the energy penalty for Al-O-Al bonds is smaller in Ca aluminosilicates than in Na aluminosilicates. For the Si 2 B 2 O 4 H 8 (CH 3 ) 2 and Si 2 B 2 O 4 H 8 Ca molecules the paired geometry is again the more stable. Underbonded O atoms in B-O-B linkages are found to be stabilized more strongly by counterions than are those in Al-O-Al linkages. This provides an explanation for the different T,T ordering patterns in anorthite, CaAl 2 Si 2 O 8 , and danburite, CaB 2 Si 2 O 8 . Our results also indicate that it may be possible to systematically synthesize gas phase and condensed phase species in which the Al avoidance rule is violated.We have also used the S4R species to model rings in Na aluminosilicate glasses and their reaction with H 2 O. Calculated NMR shieldings are reduced (deshielded) by about 5-6 ppm for both Si and Al when two Na + ions are coordinated to Si 2 Al 2 O 1 2 H - 2 8 . Reaction of H 2 O with Si 2 Al 2 O 1 2 H 8 Na 2 does not cause hydrolysis of the Si-O-Al bond or protonation of the bridging O, rather the H 2 O coordinates strongly to Na + while H-bonding to the bridging O. This reaction is exoergic by about 35 kJ/mol and produces a slight shielding of the Si and a reduction in the quadrupole coupling constant of the Al. No single species was found to be consistent with all the NMR spectral data for hydrous aluminosilicate glasses.