It is one of the sodium silicates, specifically a pyrosilicate, formally a salt of the unstable pyrosilicic acid H6Si2O7.

The Si2O6−7 anions are arranged in layers parallel to the (100) plane, with the sodium cations distributed in 24 distinct crystallographic positions, coordinated by 4 to 6 near oxygen atoms.

Some of the 4-coordinated sodium atoms can be interpreted as parallel columns of edge-sharing NaO4 tetrahedra.

The columnar arrangement forms tunnels that house the remaining sodium cations.

Twinning at a microscopic scale simulates a much larger monoclinic C centered lattice (V′ = 6220 Å3, Z = 32).