Broadly speaking, my goals as a geochemist and mineralogist are to probe the secrets of how Earth materials work, and to use that understanding to predict and design new functionality. I have focused on the molecular-scale characterization of Earth materials in a variety of environments. I seek to quantify surface reactivity, evolution over time, and the capacity of minerals to sequester ions, crystallize, and survive in a variety of extreme environments. By deciphering mechanisms at the atomic and molecular levels, we can understand, predict, and even manipulate mineral behaviors and properties at the macroscopic scale.
Nanoporous minerals, including the naturally occurring zeolites, are well known for their variety of uses in geological, environmental, industrial, and even medical applications. Certain nanoporous minerals, such as sitinakite, are ideal for nuclear waste sequestration due to their remarkable resistance to extreme pH and high gamma radiation, adjustable tunnel structures, and exceptionally high ion selectivity. Sitinakite is currently in use at Savannah River and Hanford sites for remediation of their on-site leaks. Sitinakite, and other newly discovered nanoporous minerals, are showing great promise for environmental remediating technologies. Nanoporous minerals easily exchange cations/anions from their large structural voids for other like-charge ions in the immediate environment. The mechanisms of ion exchange processes are often not well understood owing to the varied chemical conditions, thereby limiting their environmental and industrial applications. Environmental effects such as hydration, exchanger composition, ion valence contrast, and many other factors play significant roles in determining the pathways of ion exchange processes. I have been able to determine, for the first time, the fundamental molecular mechanisms that control ion exchange processes in sitinakite and other porous structures. Although the precise ion diffusion pathways vary with mineral species, my work and that of my colleagues have demonstrated that mapping the structural role of H2O within porous frameworks and layered materials is critical for understanding and controlling ion selectivity.
A topic hotly debated (mostly outside the scientific community) concerns the effects of asbestos minerals on human health. Research has shown that certain asbestos minerals (e.g., crocidolite) present more health risk than others, so there is renewed interest in determining how fibrous byproducts develop in amphibole and other deposits. In collaboration with Mickey Gunter (Univ. of Idaho), we are mapping the geochemistry and mineralogy during formation and alteration of asbestos minerals in order to better understand the effects of hydration during recrystallization of fibrous silicates. Preliminary results show that asbestos talc in the Gouverneur mining district in New York forms during dehydration of non-asbestos actinolite. Future investigations of health effects associated with mine dust in these areas will rely on more detailed studies of asbestos mineralogy, morphology, composition, and formation.
Fibrous minerals are not limited to near-surface dust and the risk to human health from mining could be more extensive than previously thought. My work in very low temperature mineralogy in collaboration with John All (WKU) has shown that dust trapped in snow in the high-altitude Peruvian Andes, which has been transported to ~5000-7000m in the atmosphere, contain significant quantities of asbestos talc as well as faceted copper- and mercury-bearing minerals. We wish to determine the provenance of these minerals (likely related to mining at lower elevations) as well as understand geochemical reactions that take place in the atmosphere during transport. Crystallography and crystal chemistry of the copper and mercury phases suggest that they form in the atmosphere and are trapped in the snow and could be a source of water nucleation for cloud formation, in addition to the abundant potassium feldspar presence. Are high-altitude, asbestos and copper-mercury minerals primary or diagenetic, and what might be the regional or global impact?
A major question in Earth science, still unresolved, is what drove past sea level changes? Based on the composition of fluid inclusions in halite, there is little question that the seawater concentrations of some major ions (e.g., Mg, Ca, SO4) have changed by a factor of three or more through the Phanerozoic. However, these changes are constrained by just a few datasets due to the paucity of the evaporite record. Transitions from high to low Mg/Ca oceans are poorly defined by existing records, but are important to understanding global controls on ocean chemistry. A collaborative group including Troy Rasbury (Stony Brook), Gary Hemming (Queens College), myself, and others are working to better define the record across calcite (low Mg/Ca) to aragonite (high Mg/Ca) sea transitions, and to use our measured data as a test for a future integrated Earth system model. My main contribution is determining the mineralogy and Mg/Ca of echinoderms representing key changes in ocean chemistry through the Phanerozoic. Slight changes in global seawater chemistry can have a profound impact on the crystal chemistry and structure of the minerals, be it calcite or aragonite, which are biologically mineralized. By determining the composition, crystal structures, and crystallization/preservation pathways of the organisms’ tests, we are developing a detailed proxy record of ocean chemistry through time.
In addition to the marine record, I am also interested in terretial proxies. The image to the right (bottom) shows the mole percent magnesium carbonate in a speleothem. These data clearly indicate that signifcant variation occured in this cave over the last ~1,500 years.
Commercial production of new materials for industry takes, on average, 20 years. Application of minerals is a vital component to industrial progress: for example, manganese oxide based batteries, fluid catalytic cracking of hydrocarbons, nanomaterials for highly selective sensors, photovoltaic materials, environmental remediation of radioactive waste, colossal magneto-resistance and super conductivity are all based (at least initially) on structures of naturally occurring minerals. In addition to technology-based applications, understanding of mineral genesis and evolution at both low and high pressure/temperature, is essential to deconvoluting dynamic Earth processes.
The Materials Genome Initiative is a massive experimental, theoretical, and data science undertaking to discover the makeup of minerals/materials from sub-atomic particles through materials fabrication and application. My work in this area brings expertise from an experiential and theoretical kinetic perspective where experiments are performed in real-time to capture atomic/molecular motions from liquid-to-crystal, bulk physical and chemical properties, and their responses to extreme environments (X, P, T). From this, the applicability of advanced materials to a variety of topics, such increased oil/gas refinement efficiency, environmental security of nuclear stockpiles, reduction of foreign energy and critical material dependence, carbon/heavy metal sequestration, environmental remediation of natural waters, and mineralogical responses to climate change, can be considered.