Stephen J. Guggenheim, PhD

I define research problems that are of special significance in mineralogy and materials science. Generally, these problems relate to the understanding of phyllosilicate (clay mineral) stability by understanding atomic structure. I try to “re-invent” myself every 7 to 8 years, so that I work on new topics that allow a greater understanding and appreciation of phyllosilicates in general. Thus, instead of one or two research areas involving special techniques or research with two or three minerals, I have many directions of research, capitalizing on diverse techniques (e.g., XRD and high-temperature and high-pressure powder and single-crystal XRD, HR TEM, high-pressure DTA, optical harmonics, computer simulations of crystal structures, etc) to solve problems in all the phyllosilicate mineral groups.

1. Current/future research plans: environmental chamber for liquid/gas/solid interactions. An X-ray based high-pressure environmental system for studies to 1000 bars pressure and from 0 to 200 oC, i.e. deep crustal conditions, was designed to investigate possible reactions between seawater (or brines) and sediment under controlled conditions in real time. The high-pressure environmental chamber (HPEC) will use brines plus solids (or micro-organisms) in suspension that can be pressurized with various gases (e.g., CH4, CO2, O2). The HPEC is equipped with injection and extraction valves to allow the chemistry of the sample environment to be changed and analyzed and an internal pump to obtain a dynamic flow to maintain equilibrium conditions. The HPEC can mimic the deep crustal environments, and I anticipate that it will lead to a new, transformative paradigm of how rocks, oceans, and possibly life are interconnected. Besides bore-hole environments, a wide-range of applications in materials science, climate-related studies (e.g., CO2 sequestration), etc. is possible because materials and reactions can be studied with almost any liquid/gas as a component.

2. Current/future research plans: Clay-hydrate intercalates and an environmental chamber for gas/solid interactions. Methane hydrates are ubiquitous on the ocean floor and represent a vast reservoir of methane, a greenhouse gas. A low-temperature (0 - 150 oC), elevated-pressure (to 70 bars) powder X-ray diffraction environmental chamber was developed to study primarily gas/solid interactions for hydrate formation intercalated in the clay structure. Methane hydrates do indeed intercalate in swelling clays, suggesting an additional reservoir for methane that may have important implications for climate change, for energy-resource development, for understanding geologic hazards on the ocean floor, and for energy-exploration strategies. There are also important implications for clays on Mars, where methane and carbon dioxide may be candidates for clay intercalates located at the Martian poles. Studies are now involving mineral alterations in H2O using static experiments with CO2 gas.

4. Dehydration and dehydroxylation reactions. The role of water (H2O, OH) in reactions involving phyllosilicates is fundamental in sedimentary, metamorphic, and diagenetic processes, as well as in many industrial and engineering applications. My research combines high-temperature, X-ray diffraction techniques with high-pressure DTA to propose atomistic models for these reactions, in addition to the description of the thermodynamic properties. Studies have included a wide range of interlayer cation-exchanged smectite minerals to understand the dehydration and dehydroxylation of these minerals. During the same period, high-temperature studies of the atomic structure of muscovite (for dioctahedral micas), phlogopite (for trioctahedral micas), lizardite (for serpentines), and chlorite were made to understand how phyllosilicate atomic structures respond to temperature increases. The muscovite structure paper was seminal in the use of Pauling’s rules to develop an atomistic dehydroxylation model. I was quite pleased that this approach was used later by Drits and co-workers to develop models for the dehydroxylation of cis-vacant micas.

5. Modulated phyllosilicates. The characterization of modulated layer silicates is important in the understanding of topological limits and possible chemical variations of common layer silicates. This work emphasizes the use of high-resolution transmission electron microscopy (HR TEM) and electron diffraction to determine the complex crystal structures of the modulated phyllosilicates. Structural models were developed that allowed the prediction of which structures of some phyllosilicates should be considered candidates for structural modulations. In addition, a general classification scheme was developed for the modulated phyllosilicates. Much of the TEM work on developing structural models was done in the 1980s, long before most workers (at least in the West) recognized that structures could be obtained from TEM intensity data.

6. Structure studies of phyllosilicates. Understanding the crystal structures of layer silicates is fundamental in predicting the physical and chemical properties of these materials. Current work involves X-ray structural studies at high temperatures (see dehydration and dehydroxylation studies), in addition to examining phyllosilicates of unusual chemistries. My earlier studies, in collaboration with my doctoral advisor, S.W. Bailey, developed models of cation ordering in subgroup symmetries, in particular, for mica minerals such as margarite, lepidolite, and zinnwaldite. The idea that ordering effects could only be recognized by considering subgroup symmetries of the space groups was novel, and we were the first to develop techniques where subgroups could be tested.

• Guggenheim, S. and Koster van Groos, A. F. (2015) An integrated experimental system for solid-gas-liquid environmental cells. Clays and Clay Minerals(in review).
• Guggenheim, S. (2014) Introduction to Mg-rich clay minerals: Structure and composition. In Magnesian clays: Characterization, origin, and applications. AIPEA Publication No. 2, M. Pozo, Ed. (in press).
• Guggenheim, S. (2014) Phyllosilicates used as nanotube substrates in engineered materials: Structures, chemistry, and textures. In Research Progress in Natural Nanotubes, Churchman, J. and Pasbakhsh, P., Eds., Apple Academic Press (CRC Press), New Jersey, USA. (in press).
• *Elmi, C., Brigatti, M.F., Guggenheim, S., Pasquali, L., Montecchi M.,and Nannarone, S. (2014) Crystal chemistry and surface configurations of two polylithionite-1M crystals. American Mineralogist, 2049-2059.
• *Elmi, C., Brigatti, M.F., Guggenheim, S., Pasquali, L., Montecchi M.,and Nannarone, S. (2014) Crystal chemistry and surface configurations of two iron-bearing trioctahedral mica-1M polytypes. Clays and Clay Minerals, 62, 243-252.
• *Martos-Villa, R., Guggenheim, S., Mata, M.P., Sainz-Diaz, C. I., and Nieto, F. (2013) Interaction of methane hydrate complexes with smectites: Experimental results compared to molecular models. American Mineralogist, 99, 401-414.
• *Johns, C. A., *Martos-Villa, R., Guggenheim, S., and Sainz-Diaz, C. I. (2013) Structure determination of trimethylsulfoxonium-exchanged vermiculite. Clays and Clay Minerals, 61, 218-230.
• *Martos-Villa, R., Guggenheim, S., and Sainz-Diaz, C. I. (2013) Interlayer water molecules in organocation-exchanged vermiculite and montmorillonite: A case study of tetramethylammonium. American Mineralogist, 99, 1535-1542.
• *Elmi, C., Brigatti, M.F., Guggenheim, S., Pasquali, L., Montecchi, M., Malferrari, D., and Nannarone, S.(2013) Sodian muscovite-2M1: Crystal chemistry and surface features. Canadian Mineralogist, 51, 5-14.
• *Giesting, P., Guggenheim, S. Koster van Groos, A.F., and Busch, A. (2012) Interaction of carbon dioxide with Na-exchanged montmorillonite at pressures to 640 bars: Implications for CO2 sequestration. International Journal of Greenhouse Gas Control, 8, 73–81.
• *Giesting, P., Guggenheim, S. Koster van Groos, A.F., and Busch, A. (2012) X-ray diffraction study of K- and Ca-exchanged montmorillonites in CO2 atmospheres. Environmental Science & Technology, 46, 5623-5630.
• Drits, V.A., Guggenheim, S., Kogure, T., and Zviagina, B.B. (2012) Structures of the 2:1 layers of pyrophyllite and talc. Clays and Clay Minerals, 60, 574-587.

BS Geology, 1970, Marietta College

MS Geology, 1972, Stony Brook University

PhD Geology, 1976, University of Wisconsin-Madison