A GEOCHEMICAL AND MINERALOGIC COMPARISON BETWEEN GEOPHAGOUS CLAYS AND NON-GEOPHAGOUS CLAYS FROM THE HOUSTON,TEXAS AREA

Geophagy is the deliberate consumption of earth materials, most commonly practiced amongst pregnant women. Uncertainty exists concerning the causative factors responsible for this behavior. This study is an attempt to identify the chemical/mineralogical differences between commercially available geophagous clays (from Nigeria, Lagos, and Mexico) and non-geophagous clays from the Houston, TX area. Three commercially available geophagous forms are common: flat, dark, shaley fragments, and pale samples hand-shaped into either barrel-like or spheroid forms. XRD patterns indicate that geophagous clays are kaolinite-rich (+montmorillonite+illite); high background readings suggest that the shaley samples are organic-rich. Shaley fragments have higher FeO, MgO, CaO, K2O, Co, and Zn (150-200 ppm), whereas spheroids have higher TiO2, Al2O3, Na2O, V, Ba, and Zr contents. Barrel-shaped samples have the highest Al2O3 (>35 wt.%) and Cs contents. Although all forms have similar LREE-enriched patterns with negative Eu-anomalies, each group exhibits different La/Lu. These differences suggest different sources, and may indicate different nutritional/physiological contributions to geophagists’ diets. In comparison, non-geophagous clays from SE Texas are more quartz-rich, and have higher Zr and Hf contents, suggesting derivation from A-type granite. Samples were digested in HCl to simulate digestion in the human stomach, and the leachates were analyzed. Geophagous clay samples yielded similar Pb contents (10-19 micrograms/gram). Solubility of the analyzed metals is greatest in the shaley samples, followed by spheroid and then barrel-shaped samples (which yielded only 10% soluble Fe and Zn). We suggest that the kaolinite-rich spheroid and barrel-shaped samples are consumed for their ability to soothe upset stomachs (e.g., “morning sickness”), whereas the shaley samples are more beneficial as dietary supplements (especially Fe, Ca, and Zn). Low kaolinite contents make the Houston-area clays undesirable for soothing upset stomachs, but the high solubilities of Fe (49-92%), Ca (58-96%), and Zn (35-69%) suggest they could be consumed as a dietary supplement. However, this conclusion should be viewed with caution in light of their high soluble Pb (up to 160 micrograms/gram) and As (<28 micrograms/gram).