Effective radium-226 concentration, EC_Ra, is the product of radium activity concentration, C_Ra, multiplied by the emanation coefficient, E, which is probability of producing a radon-222 atom in the pore spaces. It is measured by accumulation experiments in the laboratory, achieved routinely for a sample mass >50 g using scintillation flasks to measure the radon concentration. We report on 3370 EC_Ra values obtained from more than 11 800 such experiments. Rocks (n=1351) have a mean EC_Ra value of 1.9±0.1 Bq kg⁻¹ (90% of data in the range 0.11–35 Bq kg...