Experiments indicate that gypsum can be precipitated by the mixing of seawater brines of different stages of evaporation, in addition to the previously recognized mechanisms of direct evaporative crystallization and crystallization due to temperature changes. A proposed geologic model shows how gypsum precipitation by brine mixing might occur in an evaporite basin. Conclusions based on the experiments and their relations to the geologic model are as follows.

1. Precipitation of gypsum can occur in a marine evaporite basin by mixing brines of different composition and specific gravity.

2. Precipitation occurs without further water loss by evaporation.

3. Precipitation can occur from a brine that was undersaturated before mixing.

4. The only form of calcium sulfate to precipitate in these experiments was gypsum.

5. Brine mixing could cause different salts to be deposited simultaneously in different parts of a basin depending on the stage of the evaporite cycle.