The deterioration of stone in the Karanis, Egypt North Temple (Roman Period) was studied by x-ray diffraction and atomic absorption analyses. The cause of deterioration is biological, due to the existence of fossils in the Temple's stone and remains of bones leading to the crystallization of columnar crystalline material at the roof of the Priest's room. X-ray diffraction analysis of this crystalline matter showed that it consists essentially of iron oxalate, oxalic acid, and potassium ammonium phosphate, in addition to traces of sulphate, manganese, magnesium, calcium, and sodium ions. -- AATA