Numerous clay pits containing an abundance of material suitable for the clarification and purification of petroleum products are operated along the Texas Gulf Coastal Plain. Much of the original material has altered sufficiently to form adsorptive clay of usable quality. Optical, chemical, and x-ray studies indicate that the principal mineral constituent of the clays as mined is montmorillonite. Microscopic textures and structures, when well preserved, are significant of origin.
Many beds represent the result of alteration in situ of volcanic ash. However, substantial amounts of kaolinite, halloysite, and allophane occur in some deposits. In certain deposits alteration has been so complete as to obliterate direct evidence of the origin of the clay.
The waxy character of many moist clay layers is a convenient indicator in the field. Laboratory study shows that waxy clays contain more nearly pure montmorillonite than other types which are soft,, granular, and kaolinitic. The luster may be attributed to unusual hydration characteristics of montmorillonite. Kaolinitic mixtures occur in the northeastern part of the clay belt, whereas the more nearly pure montmorillonite occurs in the southwestern part.
A review of the literature, correlated with field observations, indicates that the fuller,s earths of eastern Texas formed during the Eocene, and Oligocene or Miocene epochs. Correlation of physical, chemical, and opticai properties with adsorptive capacity has been attempted. The influence of mineralogical features on adsorptive capacity may be summarized as follows: impurities lower adsorptive capacity; microscopic structures and textures are apparently not related to adsorptive efficiency; the montmorillonite lattice structure permits high adsorption; amount and degree of alteration of original material to clay materially affect adsorptive capacity; origin by transportation of clay introduces granular impurities and lowers adsorptive power; high percentages of removable bases and water seem to accompany high adsorptive capacity; montmorillonite is the most highly adsorptive clay mineral studied.