A method of producing calcium sulfate &agr;-hemihydrate is disclosed, including the steps of exposing a mixture including a calcium sulfate form selected from the group consisting of calcium sulfate dihydrate, calcium sulfate &bgr;-hemihydrate, water-soluble calcium sulfate anhydrite, and mixtures thereof, water, and a crystallization catalyst, to microwave radiation to produce calcium sulfate &agr;-hemihydrate; and separating at least a portion of the calcium sulfate &agr;-hemihydrate to provide a solid comprising calcium sulfate &agr;-hemihydrate and a filtrate and/or remainder that can be recycled to provide at least one of a calcium sulfate form, water, a crystallization catalyst, a crystal habit modifier, and a surfactant for use in production of additional &agr;-hemihydrate.