Nanoscale Structure and Chemistry of Minerals and Mineral Coatings

建议的研究应用先进的透射电子显微镜（TEM）来研究矿物学、岩石学和地球化学问题。这项基于成就的更新提案所包含的项目旨在了解矿物的晶体化学及其在亚纳米尺度上的反应。许多浅层砂和砂岩含水层的颗粒具有通常被认为是铁/铝氧化物和氢氧化物的涂层，但TEM研究表明它们主要是无定形和低结晶的硅酸盐材料。科德角受污染含水层的涂层将被详细描述；包括与锌水溶液反应的样品。结果将显示哪些相对金属的吸附和渗透深度负责。进一步的研究将评估矿物中扩展缺陷的化学分离。分析钙白云岩中的c域结构和奥辉岩中的孪晶界可以发现钙的富集或富集。为了阐明这种变质反应，我们将对多阶段由花青石取代放线石的反应顺序进行跟踪。NSF的支持将继续为约翰霍普金斯大学的教育和先进仪器基础设施做出重要贡献。它还将产生对矿物分子尺度过程的新认识。社会将从这项研究中受益，因为它改进了对覆砂含水层中有毒金属的建模，这可能会影响我们饮用和农业用水的质量。

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.