Glauconite occurs in the sediments from an area on the continental shelf off the Washington-Oregon coast. The mineral is forming apparently at the present time, although some of it may be derived from Tertiary sedimentary rocks exposed on the shelf.

The glauconite-rich sediment shows a linear correlation with boron, which averages 223 ppm. Boron and potassium indicate that the mineral is a mixed-layer montmorillonite-illite. The chemical composition of the sediment is nearly the same as that reported by other investigators for glauconite-rich sediment and sedimentary rocks.

Petrographic evidence indicates several modes of origin for the glauconite including the glauconitization of specific minerals, lithic fragments, fecal pellets, and clay material within shells.

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