A new mineral species, apoanalcite, has recently been described in this Journal by Chr. Oftedahl. The chemical composition is shown in table 1. When calculated on 6 0-atoms ( + l ,51 0) the analysis gives the formula Na_{0,92 Ca0,3} Al_1,55  Si_1,59 0₆ • 1,51 H₂O, and Oftedahl has accordingly suggested the following gross formula for apoanalcite: NaAI (Ai_x Si_Y)SiO₆ · 1,50 H₂O, where 3x + 4y = 4, implying that a mutual exchange of Al and Si can take place in the anionic part of the lattice, leaving some of the Al-Si-positions vacant when Si takes the place of AI.