Pelletal phosphorites occur in the Ordovician Stairway Sandstone of the Amadeus Basin. They commonly contain abundant detrital quartz grains that are markedly finer grained than the detrital quartz which encloses the phosphatic pellets. It can be shown that after the phosphate pellets were formed the sediments were winnowed, the fines removed, and only the coarsest quartz grains and the phosphatic pellets and nodules remained.

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