This study provides quantitative data for evaluating the significance of fluviodetrital glauconite in geochronology samples. Natural occurrences of glauconitic source rocks and stream deposits were collected. Their sorting and mineralogy (per cent of glauconite) are reported. Results of abrading glauconite in the laboratory are also reported. Glauconite eroded from the outcrop decreases rapidly downstream until less than 0.10 per cent is present 50 miles below the outcrop. Fluviodetrital glauconite is insignificant in geo-chronology samples except for samples containing less than 2 per cent glauconite.