A porous crystalline material is described having the chabazite framework type and having a composition involving the molar relationship: X.sub.2O.sub.3:(n)YO.sub.2, wherein X is a trivalent element, such as aluminum, boron, iron, indium, and/or gallium; Y is a tetravalent element such as silicon, tin, titanium and/or germanium; and n is greater than 100 and typically greater than 200, such as about 300 to about 4000, for example from about 400 to about 1200. The material is synthesized in a fluoride medium and exhibits activity and selectivity in the conversion of methanol to lower olefins, especially ethylene and propylene.