Abstract: Ferrierite has been found at Tapu, Coromandel Peninsula, New Zealand, as a mineral vein with calcite in altered hornblende andesite lava of the Miocene Beeson's Island Volcanics. The ferrierite is low in SiO₂ (63.67%) and high in Al₂O₃ (13.75%), MgO (3.48%), and BaO(2.35%). The large a axis and cell volume (a 19.236(4), b 14.162(6), c 7.527(3) Å, V 2050 ų) are consistent with the low SiO₂, high Al₂O₃, high MgO chemistry. Optical orientation and optical sign (a = Z, b = X, c = Y, 2V(-)55°) of the mineral are different from those of the Lake Kamloops ferrierite reported by Graham (1918). Refractive indices α 1.487, γ 1.489, and density 2.136 were measured. Cleavage observed on (100) is perfect and on (001) is imperfect. Using data from eighteen occurrences so far reported including the Tapu mineral, the crystal chemistry of ferrierite has been studied.