Opoka, as a silica-calcite sedimentary rock, occurs in south-eastern Europe and Russia. Stratigraphical studies down to 8 m depth were performed in Bełżec, Poland, where samples were taken for further analyses. Vertical layers represented a heavy-weight opoka consisting of relatively more CaCO3 than the horizontal layers of lightweight opoka dominated by SiO2. Opoka had a mean bulk density of 1.34 g/cm3, a porosity of 44.5 % and a specific surface area of 64 m2/g. Opoka, especially after heated to over 900oC can be used as reactive filter media for phosphorus removal. Maximum sorption capacity was 119.6 g PO₄ -P/ kg. Element analysis of the rock did not reveal any anomaly from that expected, and it was concluded that its element content does not devaluate opoka as a sorbent used in ecological wastewater treatment