A crystalline material is described that has an AEI framework type, wherein the material, in its calcined, anhydrous form, has a composition involving the molar relationship:

(n)X₂O₃:YO₂,

wherein X is a trivalent element, Y is a tetravalent element n is from 0 to less than 0.01. The material is normally synthesized in a halide, typically a fluoride, medium and exhibits activity and selectivity in the conversion of methanol to lower olefins, especially ethylene and propylene.