The Holocene lacustrine diatomaceous earth of Fayium, South West of Cairo, has been studied to define its minerals, chemistry, petrography and physical properties. Minerals were processed by way of calcination at 550℃, followed by acid leaching to reduce levels of mineral impurities. The diatomite is of biogenic opal A, with calcite as the main gangue mineral, quartz and clay minerals (smectite followed by kaolinite in abundance and a trace amount of illite). Silica in the diatomaceous earth accounts for about 63% on average.; Positive correlation between CaO and CO-2 indicates that Ca is present mainly as calcite. Al-2O-3, Fe-2O-3, MgO and K-2O are attributed mainly to clay minerals. However, the physical properties of the diatomaceous earth as filter aids and filler for paints and plastics are poor because of general high levels of impurities. The technological performances of the diatomaceous earth have been significantly improved owing to upgrading of diatoms through mineral processing trials. The Holocene lacustrine diatomaceous earth of Fayium, South West of Cairo, has been studied to define its minerals, chemistry, petrography and physical properties. Minerals were processed by way of calcination at 550 ° C followed by acid leaching to reduce levels of mineral impurities. The diatomite is of biogenic opal A, with calcite as the main gangue mineral, quartz and clay minerals (smectite followed by kaolinite in abundance and a trace amount of illite). Silica in the diatomaceous earth accounts for about 63% on average. ; Positive correlation between CaO and CO - 2 indicates that Ca is present mainly as calcite. Al - 2O - 3, Fe - 2O - 3, MgO and K - 2O are attributed mainly However, the physical properties of the diatomaceous earth as filter aids and filler for paints and plastics are poor because of general high levels of impurities. The technological performances of the diatomaceous earth have been significantly improved due due to upgrading of diatoms t hrough mineral processing trials.