Transmission electron microscopy (TEM) study of palygorskite-sepiolite minerals

This work is a transmission electron microscopy (TEM) study of palygorskite-sepiolite minerals with both sedimentologic and mineralogic components and provides mineralogic explanations for variation in bulk clay properties. TEM investigation of palygorskite from sedimentary deposits in the Hawthorne Formation support environmental interpretations of previous workers and provide additional details about processes that operated in the Apalachicola embayment. Epitaxial overgrowth of R0 (Reichweite = 0) illite-smectite, and R1 illite-smectite on detrital particles of kaolinite and illite indicate a stratified water column was present. Hydroxyapatite is a common mineral in the Hawthorne Formation samples occurs as recrystallized fecal pellets with diameters of several micrometers, as clusters of small crystals with diameters of a few hundred nanometers, and also as single crystals that are commonly 50 nm in length. The clay-sized hydroxyapatite may be the cause of variable sorption performance of palygorskite clays from the Hawthorne Formation as dissolved phosphate anions interfere with organo-clay reactions.; Yofortierite, a Mn-analog of palygorskite was examined using TEM. Experimental imaging, selected area electron diffraction (SAED), and computer modeling indicate that the space group for much of the material is A2/ m. The structure is similar to an A2/m Mn-tupersuatsiaite-based structure. Experimental images and SAED indicate that widths of 2:1 layer ribbons (polysomes) vary. Computer modeling proved useful, however producing a close match between experimental and simulated images is very difficult and is believed to arise from the dynamic behavior of the minerals in the electron beam.; Defects are common in palygorskite-sepiolite minerals. Low-angle planar defects are common in the center of fibers and high-angle planar defects are common near surfaces of fibers, particularly in palygorskite from the Hawthorne Formation. One of the most significant defects observed in this study is the omission of one or multiple polysomes. These defects explain high water contents of palygorskite-sepiolite minerals, and explain some interactions of palygorskite-sepiolite minerals with organic molecules. The origin of the polysomes omission defects is likely related to rapid crystallization.