Oil shale from the lower part of the Eocene Green River Formation in the Piceance Creek Basin, Colorado, averages 0.13 weight percent fluorine, which is about twice that found in common shales, but is the same as the average amount found in some oil shales from other parts of the world. Some fluorine may reside in fluorapatite; however, limited data suggest that cryolite may be quantitatively more important. Analysis of 913 samples from two core holes that penetrate the lower 375 m of the oil-shale deposits found fluorine to range from 0.001 to 2.2 weight percent; about 90 percent of the samples con tain between 0.001 and 0.20 weight percent fluorine. The analyzed sequence consists of mostly nahcolitebearing dolomitic oil shale, except for the lower 55-75 m, which consists of illitic oil shale. The fluorine content of much of the nahcolitic oil shale is somewhat lower, and much more variable from sample to sample, than that of the underlying illitic oil shale. Vertical profiles of the fluo rine content for the two core holes through the same stratigraphic interval are essentially dissimilar. The abundance of fluorine seems unrelated to shaleoil content, except in the R-5 zone and near the base of nahcolite-bearing oil shale where there is a moderate positive association. Fluorine and phos phorus abundances show mostly little or no assoc iation, and only moderate positive association in some scattered samples.
