Nanoscale Structure and Chemistry of Minerals and Mineral Coatings

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The proposed research applies advanced transmission electron microscopy (TEM) to problems in mineralogy, petrology, and geochemistry. The projects encompassed by this Accomplishment-based renewal proposal aim to understand the crystal chemistry of minerals and their reactions at the sub nanometer scale. The grains of many shallow sand and sandstone aquifers possess coatings that are commonly assumed to be Fe/Al oxides and oxyhydroxides, but TEM studies show they are predominantly amorphous and poorly crystallized silicate materials. Coatings from a contaminated aquifer on Cape Cod will be characterized in detail; including samples reacted with aqueous Zn solutions. Results will show which phases are responsible for metal sorption and penetration depth into the coating. Additional studies will assess chemical segregation on extended defects in minerals. Analysis of c domain structures in calcian dolomite and twin boundaries in augite will detect Ca enrichment or depletion. The sequence of reactions during multistage replacement of actinolite by anthophyllite will be tracked to illuminate such metamorphic reactions. Renewed NSF support will continue to make important contributions to education and advanced instrumentation infrastructure at Johns Hopkins. It will also produce new understanding of molecular-scale processes in minerals. Society will benefit from the research through improvements in modeling toxic metals in coated-sand aquifers, potentially affecting the quality of water we drink and use in agriculture.