Scan electron micrographs (SEMs), are shown of three representative types of Georgia kaolin: ‘soft’, Cretaceous-age clay; ‘hard’, fine-grained clay; and ‘flint kaolin’.

Sparta Granite and a thick deposit of its overlying saprolite are taken to serve as examples of probable source rock for Georgia kaolin. SEMs are presented to show sequential argillation of this fresh granite through a transition zone to the saprolite. The saprolite contains abundant books of kaolinite similar to those occurring in Cretaceous kaolin, accompanied by some elongates, whereas in the transition zone elongates are predominant. A morphologic type of fibrous, elongate 1:1 clay mineral, hitherto not illustrated, is shown from kaolinizing Sparta Granite, and from Pre-Cambrian saprolitic gneiss 25 km south of Athens, GA.

Whereas kaolin elongates originated in contact with feldspar in the Sparta transition zone, well-formed books of kaolinite are shown to have been formed in contact with feldspar in the saprolite from a Missouri granite. The arkose above the granite in the Missouri occurrence has altered to loosely packed books of kaolinite. The interpretation is made that book-type kaolinite, where it occurs in large deposits of saprolite or kaolin, was formed under geochemical conditions of relative chemical stability between kaolinite and feldspar, as might prevail in a geological ‘weathering crust’. It is interpreted that elongate kaolin morphology may be formed under conditions of limited or lesser geochemical stability.

SEMs show that the established book-morphology of Sparta saprolite is disarranged during secondary Holocene surface weathering and pedogenic processing.

SEMs show that books of kaolinite, although individually fragile, may be protected from destruction or delamination during artificial blunging and transport when moved within naturally coalesced pellets. Possibly original books of weathered kaolinite might similarly survive natural stream transport during sedimentational processes.

Some ‘flint kaolin’ contains molds of sponge spicules coated with low-cristobalite.

Scan electron micrographs are shown of the textures of flint clays, tonsteins, kaolin associated with combustion-metamorphism, sedimentary kaolin, and dickite from the Sydney Basin of Australia. The textures of the flint clays and tonsteins indicate those clays were derived largely from volcanic products. The clay samples were collected at stops on the Kaolin Excursion No. 4 of the August, 1976, International Geological Congress.

In like manner, kaolin samples were collected in Japan from stops made on the field excursions of the Seventh Conference of the Committee on Correlation of Age and Genesis of Kaolin which met in Tokyo, September, 1976. SEMs illustrate representative kaolins of Japan, including Gaerome and Kibushi types of kaolin, Roseki (‘wax stone’) pyrophyllite and dickite, hydrothermal kaolin at Itaya, and flint clay at Iwate. Varied morphologies of halloysite, including spherical halloysite, from the Yamaka open-pit at Naegi are micrographed.

Word descriptions of the textures are frustratingly inadequate in comparison to what may be seen at a glance in the micrographs—hence, the abstract becomes in reality a rapid view of the SEMs.

A study was undertaken to investigate the adsorption of hemin, protoporphyrin and hematoporphyrin by kaolinite and a Ca-montmorillonite in aqueous solutions buffered at pH 4 and 9.

Although experimental restrictions at pH 4 prevented the complete characterization of the adsorption isotherms, kaolinite did exhibit a saturation of exchange sites by the cationic porphyrins. Both kaolinite and montmorillonite displayed a similar saturation of sites by the porphyrins in their anionic forms at pH 9. The major differences in the adsorption isotherms are attributed to differences in the exchange capacities of the clays.

Adsorption of the porphyrins at pH 9 was inhibited largely by phosphate treatment of the clays; this effect is interpreted as blockage of the anion exchange sites by irreversibly-bound phosphate.