Abstract: An energy-saving process for the calcination of diatomite is described. Diatomite particles and water are mixed to form a mixture with a moisture content in the range of 15 to 50 weight percent and then balled to form generally spherical balls, preferably with diameters of 1.5 to 20 mm. The balled diatomite, which may also contain a flux or whitening agent, is then calcined at about 1700.degree. F. to 2350.degree. F. (923.degree. C. to 1290.degree. C.). The process reduces the time required for calcination to about 0.75 to 30 minutes from the 30 to 90 minutes required in prior art processes, and thus also reduces the amount of thermal energy required to calcine a given unit of diatomite. The balls enable calcination to be performed using an externally heated tube furnace a fluid bed or a travelling grate. Calcination is highly uniform and little attrition of balls is observed. Fine dusts of good purity as well as materials heretofore considered waste can be processed to usable products by this invention.