The effects of sintering and purification processes on the porosity and specific surface area of diatomaceous earth, mined in the Ankara region of Turkey, were investigated. The material was studied in three forms, as received, calcined, and purified. Changes in surface area occurred, with large differences between as received, calcined, and purified materials. As received material had very high pore volume, with a specific sin-face area of 204 m(2) g(-1). For purification, the raw material was treated in HCl solutions varying in concentration from I to 5N for several hours, with and without heating. The purification treatment caused reductions in BET sin-face areas, with minimum area after treatment being 136 m(2) g(-1). As received and purified samples were calcined at various temperatures. The effects of purification treatment and sintering on surface area and on the contents of undesirable aluminium, calcium, magnesium, iron, and alkaline impurities in the materials were characterised.