Summary: Chemical, optical, and X-ray data are presented on three analcimes from a differentiation sequence, olivine-theralite to analcime-tinguaite; compared with the ideal analcime composition, they reveal replacement of NaAl→Si. Optical and X-ray data on these minerals accord reasonably well with analcimes possessing similar compositions, and synthesized in the sub-solidus region in the NaAlSiO₄-NaAlSi₃O₈-H₂O system.