On the upper end of its general formula, the [Na/S/O] gene involves two Na+ ions per one SO4 tetrahedron, that is, a sodium sulfate group (Figure , left). Lower S signifies an excess of Na + , charge compensated by non-bridging oxygen species (i.e., up to 3 Na and 6 O when S is at its minimum value of 0.09). A possible structural representation of this is depicted in Figure (right), where a sulfate tetrahedron is surrounded by the additional oxyen species in a mix of bridging and non-bridging configurations between network-forming polyhedra, and chargecompensating the additional Na + ions. In effect and although the exact chemical environment is uncertain, the structural role of the [Na/S/O] gene, therefore, is that of an SO4 bridge in an Na-rich environment. This agrees with the observation of the conjugate [P/F/Al] gene discussed in the previous section. The bulk conductivity then depends on the frequency of these ionic bridging entities, which -assumedly -would interact to form ion transport channels.