X-ray characterization of green pellets from the Eocene Queen City Formation near Jacksonville, Texas, reveals that these pellets are interlayered glauconite and chlorite. Because chlorite contains no potassium, it would dilute the potassium and argon concentrations in the whole rock with respect to the glauconite. These pellets were dated using the K-Ar age method. The results give an average age of approximately 50 ± 3 m.y. for the Queen City Formation. This age may reflect the time-transgressive nature of the beds as the ages slightly south of this location are younger--45 m.y. for the overlying Weches Formation.

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