Structural relationships in tetrahedral frameworks: Reflections on cristobalite

Twinning on the unit cell level of the idealized cristobalite structure, using a mirror plane as the twin and composition plane, provides a simple relationship between 14 tetrahedral frameworks. Of these, 9 are found among the aluminosilicates with examples ranging from (stuffed) silicas to zeolites and include the framework types of nepheline hydrate I, zeolite LiA(BW), gismondine, phillipsite, merlinoite, tridymite, paracelsian, and monoclinic CaAl ₂Si ₂O ₈. Similar twinning relates the frameworks of natrolite, thomsonite, and edingtonite.