The Alabama Tertiary rock units studied include, in ascending order, the Clayton, Porters Creek, and Naheola Formations of the Paleocene, and the Nanafalia Formation, Tuscahoma Sand, and the Hatchetigbee and Tallahatta Formations of the lower Eocene.

Throughout the area the lower and middle part of the Clayton Formation and the upper part of the Nanafalia Formation contain the zeolites clinoptilolite, heulandite, and a "mixed form" with structural characteristics of both clinoptilolite and heulandite. These occur with cristobalite and montmorillonite. Heulandite and montmorillonite occur in the thicker clays of the Porters Creek Formation in western Alabama. Clinoptilolite is the predominant constituent of a lower Tallahatta clay in western and central Alabama. A cristobalitic claystone makes up the upper

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two thirds of the Tallahatta in western Alabama, whereas it is interlaminated with clinoptilolitic clays in central Alabama. In the eastern part of the state the upper Tallahatta claystone consists of cristobalite and montmorillonite.

No evidence indicates that montmorillonite is other than a detrital constituent in the clay and coarser grained sediments of the Naheola and Hatchetigbee Formations and the Tuscahoma Sand. However, montmorillonite could be considered a diagenetic mineral where it occurs as a part of a mineralogic suite that includes cristobalite and/or the diagenetic sedimentary zeolites clinoptilolite and heulandite.

Considering these mineral suites, it is suggested that clinoptilolite was formed from volcanic ash of a rhyolitic composition in a nearly closed hydrated system. Paragenetically, heulandite and then montmorillonite would develop from clinoptilolite through a desilicification process whereby cristobalite would have evolved as a byproduct. Conversely, it is plausible that, except for clinoptilolite, each zeolite species and montmorillonite were formed individually from volcanic ash in an open hydrated system. In the case of heulandite some silica would need to be deleted from the reacting system. However, montmorillonite development would entail not only a deletion of some silica but also an addition of magnesium. Therefore, similar mineral suites could evolve in either of two reacting ystems, open or closed.

Cristobalite, where it occurs as distinct but lens-like strata and not associated necessarily with the sedimentary zeolites or montmorillonite, is believed to be a primary mineral precipitated locally on a broad marine-shelf area according to Oswald's step rule.

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