Abstract: The present invention relates to a process of the preparation of ionizable calcium composition powder by powdering oyster shells and decomposing the powder. Oyster shells are dried and then powdered. This oyster shell powder is forced from a tubular feeding zone including a screw conveyor into a tubular processing zone, and during the passage through the tubular processing zone the powder is thermally and electrically treated. The processing zone has an electric heater arranged around the passage thereof, and a pair of electrodes arranged on opposite sides of the passages. The oyster shell powder, when it is passed through the processing zone, is heated by the heater and is exposed to an electric discharge by applying a high voltage between the pair of the electrodes, and as a result of this discharge treatment the product powder is highly ionizable.