Fig. 1

A framework sketch of erionite with cancrinite cages occupied by K+ ions (yellow circles), small empty double 6-ring cages, and large erionite cavities occupied by Ca++ (and Na+) (blue circles), Mg++ (small gray circles), and a fraction of K+ ions (K2 label, yellow circles). Eventually, the position labelled as Ca (in blue) also hosts Na+ ions. Atomic positions were based on data from Patel et al.19.