The natural radioactivity due to presence of 238U, 232Th and 40K in zirconium minerals used in the Iranian ceramic industry, tiles and waste sludges has been measured. The measurements were made by gamma spectrometry system with a high pure germanium (HPGe) detector connected to multichannel analyzer (MCA). The average concentrations of 238U and 232Th determined in the mineral samples (3000, 500 Bq kg-1 respectively) are much higher than concentrations found in the earth's crust. The specific activity of 238U and 232Th in tiles (62,54 Bq kg-1 respectively) are not higher than in other building materials.
The 238U concentration of sludges (150 Bq kg-1) is higher than the mean value for the earth's crust. The results are examined on the basis of the existing national limit.