Gem and Mineral Research
There are currently two major mineralogy research programs in the Department of Mineral Sciences. Jeffrey Post coordinates a research effort into the study of mineral structures and behaviors, with a focus on environmentally significant minerals. Mineral groups such as clays, manganese oxides and iron oxides tend to accumulate in soils and sediments and on rock surfaces where they interact directly with the atmosphere, hydrosphere, and biosphere. Many of these minerals are chemically active and readily absorb a variety of heavy metals, and can form as a result of biological mediation. They typically are fine-grained, and consequently even small quantities exhibit large surface areas and can significantly affect the chemistry of the local environment. Their fine-grained nature has made it difficult to study the structures and behaviors of these minerals using traditional laboratory methods. We have taken advantage of recent advances in synchrotron powder and single-crystal X-ray and neutron diffraction, as well as a variety of spectroscopic and sophisticated computer modeling procedures to attempt to provide a first order understanding of the structure and chemical properties of many of these phases.
One of the exciting developments in X-ray crystallography in recent years is the use of area detectors for crystal structure studies. In particular, when coupled with high intensity synchrotron sources, it is possible to perform detailed structural studies on samples that are at least an order of magnitude smaller than previously possible. This opens up the door to detailed structural investigations of many fine-grained minerals that until now were inaccessible by conventional methods. It is also now possible to use the rapid powder X-ray diffraction data collection capabilities of the synchrotron to monitor in real time chemical reactions involving minerals, e.g. cation exchange and dehydration reactions. Much of this work has been carried out at The National Synchrotron Light Source at Brookhaven National Laboratory in collaboration with Dr. Peter Heaney and his graduate students at Penn. State University.
During the past several years, Jeffrey Post has also been studying luminescence behaviors and defects in natural diamonds in cooperation with Jim Butler and colleagues at the Naval Research Laboratory and two postdoctoral fellows, Sally Eaton-Magaña and Eloise Gaillou. The Smithsonian Institution provides a unique opportunity to study one of the world’s great collections of natural diamonds, including the renowned Hope and Blue Heart diamonds. Ongoing studies of defects and impurities (e.g. boron and nitrogen) in natural blue and pink diamonds are using the department’s recently installed time of flight secondary ion mass spectrometer (TOF-SIMS), Gatan cathodoluminescence (CL) spectrometer attached to a FEI NOVA NanoSEM 600, and Fourier-transform infrared spectrometer and microscope. One goal of this research is to investigate the cause of color of pink diamonds and explore the relationship between boron and nitrogen in natural type II diamonds.
Michael Wise conducts research on pegmatite mineral deposits to understand the evolution of granite-pegmatite systems which includes not only the origin of pegmatites but also the derivation and evolution of granites that ultimately produce them. To achieve this goal, his research focuses on three broad areas: crystal chemistry and crystal structures of pegmatite minerals, petrology and geochemistry of pegmatites, and the evolution of mineral assemblages and granite-pegmatite systems.
Basic mineralogical studies for major and accessory pegmatite minerals include: solving and refinement of crystal structures, investigation of structural states (e.g. order-disorder) in minerals, and the effects of “pegmatophile” elements (e.g. Rb, Cs, Li, B) substitution on mineral structures. Petrographic study of pegmatite textures is fundamental to understanding the nucleation and growth of giant crystals. Multi-generations of tourmalines, feldspars, micas, garnets, and Nb-Ta oxide minerals are typical of many chemically evolved pegmatites and the trace element signatures of these minerals help to decipher changes in melt and fluid composition during pegmatite consolidation. Field-based studies of the internal zoning of individual pegmatites and regional distribution of granite-pegmatite systems help to understand the processes responsible for pegmatite generation.
The focus of the pegmatite program has shifted over the years from the original studies of individual pegmatites in Maine, Virginia, and Canada to pegmatite localities across the country with a greater emphasis on pegmatite occurrences and their relationship to tectonic settings. In addition, non-granitic pegmatites (e.g. mafic and alkalic pegmatites) are also being investigated. As a result of this expanded scope, the program has now become recognized nationally and is one of a handful in North America dedicated to this type of research.
During the past several years, Michael Wise has also been studying the geology of emerald deposits in North America in collaboration with Canadian colleagues Lee Groat (University of British Columbia), Scott Ercit (Canadian Museum of Nature) and Alan Anderson (St Francis Xavier University). In collaboration with Nancy McMillan (New Mexico State University) and Russell Harmon (US Army Research Laboratory), studies are being conducted on pegmatite and gem minerals using Laser-Induced Breakdown Spectroscopy (LIBS), a relatively new micro-analytical technique that has only recently being applied in the field of mineralogy.
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