Hydrocarbon conversion processes such as alkylation and hydrocracking are described which use as the catalyst a novel beidellite clay. The clay has the empirical formulaA.sub.x (Al.sub.4)(Si.sub.8-x Al.sub.x)(O.sub.20)(OH).sub.4-u F.sub.uwhere A is a cation such as an alkali metal, x is the moles of A and varies from about 0.1 to about 2, and u varies from about 0.1 to about 3.5. The clay is prepared from a reaction mixture containing reactive sources of aluminum and silicon, a cation salt, a fluoride source and water.