A synthetic gasket material for use in a high-pressure press includes a major proportion of clay mineral powder having sufficient lubricity to flow in a high-pressure press, a minor proportion of at least one hard material powder having a sufficiently greater hardness than the clay mineral to retard flow of the clay mineral and form a seal during pressing in a high-pressure press, and a sufficient amount of binder to form an integral body. The synthetic gasket material is formed by thoroughly mixing together in desired proportions the clay mineral, hard material, and binder. The mixture is compacted into a body near net geometry and having a desired configuration to facilitate use in the high-pressure press. The compacted body is heated for a sufficient time and at a sufficient temperature to remove non-crystallographic water. A synthetic gasket material prepared according to principles of this invention displays improved flow, pressure transmitting, and thermal insulating properties when compared with gasket material made from natural pyrophyllite, due to the improved compositional consistency, i.e., lack of impurities and consistently low moisture content, of the synthetic gasket material.