Dissimilar Fabrics by Scan Electron Microscopy of Sedimentary Versus Hydrothermal Kaolins in Mexico

Abstract

Abstract--Dissimilar fabrics, observed by scan electron micrography (SEM) on freshly broken surfaces of kaolins from weathered, water-laid material vs hydrothermally altered material in Mexico are illustrated, contrasted, and tentatively related to their respective environments of genesis. Coarse, open-textured, well-preserved books and vermiforms of kaolinite characterize the kaolin from water-laid material at Jacal, Mexico. Hydrothermal kaolins tend to have more tightly compacted crystals of either kaolinite flakes (individuals or in packets) or elongates (halloysite morphology) or mixtures of both in the same deposit. Variations in porosity of parent rock whether sedimentary or igneous, and dissimilar permeation by meteoric water and by vapor and liquids of hydrothermal fluids are deemed to be significant in the processes producing distinctive fabrics. The question is raised as to the fundamental distinction between kaolinite and halloysite and their nomenclature.

Chemical and mineralogical heterogeneities of weathered igneous profiles: implications for landslide investigations

“…This is mainly because of the fact that although halloysite and kaolinite belong to kaolin group (polymorphic) clay minerals, halloysite has an additional water layer in its crystal-structure compared to kaolinite. Therefore hydrous micro-environmental conditions, for instance, favor occurrence of halloysite over kaolinite (Keller and Hanson, 1975;Keller, 1976). Similarly, relatively impeded hydrological conditions favor occurrence of illite over kaolinite (e.g., Velde, 1995).…”

Scan Electron Micrographs of Kaolins Collected from Diverse Environments of Origin—IV. Georgia Kaolin and Kaolinizing Source Rocks

“…Adequate time, under uni-form, geochemical stability, would also permit large books of first-generation (neoformation) kaolinite to grow in place, as in the Missouri micrographs and the large books in Sparta (or other) saprolite of Cretaceous accumulations. It would permit secondary or diagenetic growth of large crystals, as in Figure 63 [ (0187), 750 x ], or an example from an intermontane lake basin near Jacal in Mexico [ Figure 64 (0389, 1000 x )], reported by Keller and Hanson (1975).…”

The Nascence of Clay Minerals

“…In a superjacent, open-space porous arkose derived from the same granite, the kaolinite stacks are looser and more open-textured ( Figure 9) as they also are in an unconsolidated, open-space, lacustrine deposit of arkosic sand ( Figure 10, Keller and Hanson, 1975). Weathering ofnon-feldspathic, mica-phyllite parent rock yields kaolinite growing with angular, jagged crystal edges (Figure 11, Keller et al, 1981).…”