Method for manufacturing a stable, fluid, highly concentrated aqueous suspension of calcined clay which has satisfactory rheological properties and calcined clay particles having desirable low abrasiveness. A dispersed fluid aqueous suspension of the clay containing about 50 to 55% solids is recirculated through one or more vertical agitated mills containing a particulate grinding medium such as 1/16-inch zirconia spheres. Portions of dry calcined clay are added in increments to the suspension during recirculation until the desired high clay solids level, usually 60 to 70%, is obtained.