306 Earth & Planetary Science Bldg.
1412 Circle Drive
Knoxville, TN 37996-1410
Office: EPS 317A
I am a mineralogist. Mineralogy has been through some tough times as a discipline, but it will never cease to be relevant to every aspect of geo- and planetary science. I like to tell people that mineralogy is like Dr. Who's Tardis: much bigger on the inside than it appears on the outside. In my own travels (figurative and literal) I've had the chance to explore a number of its corners:
- As a senior undergraduate and master's student, I worked on the physics of how garnet transports heat. Garnet is a somewhat common mineral at Earth's surface, most often in metamorphic rocks, but at relatively shallow depths the Earth's mantle shifts to incorporate much more garnet. In the mantle transition zone at ~400-660 km depth, garnet is a dominant mineral. The ability of garnet to conduct heat is affected by both its chemistry and its symmetry: as an isometric mineral, garnet transports heat unusually well. This enhanced thermal conductivity has the potential to short-circuit whole mantle convection by creating an extra boundary layer within the Earth where heat is transported by conduction in preference to convection. Without adequate knowledge of the mineral physics of mantle phases, decades of convective models have just used constant and not necessarily even well-chosen estimates for thermal conductivity, and this means these model results may be misleading.
- As a Ph.D. student, I used crystallography to explore the geochemistry of uranium. Why? Because uranium is at the lunatic fringe of the periodic table, that's why. The nuclear weapons and nuclear fuel cycles either have or will release a large amount of uranium from relatively stable geological reservoirs (ore deposits) into less stable ones. By studying and organizing uranium complexes in the crystalline state, and by synthesizing more, we can better understand how uranium will act in the environment and therefore how to avert human and ecological damage from the release of this toxic and radioactive "lunatic" element.
- At the University of Illinois – Chicago, I shot X-rays at swelling clays bathed in supercritical carbon dioxide. This turns out to be an interesting experiment if you want to slow or stop the rise in CO2 concentrations in the Earth's atmosphere by hiding or, more properly, sequestering it in underground reservoirs. As any good oil & gas geologist knows, reservoirs have to have caps, and caps generally derive their relative impermeability from a high clay content. In the short term, once you've injected the CO2 (as a supercritical fluid) into the subsurface, this clay is the main barrier keeping it from heading back toward the atmosphere. So what happens when the irresistible force of supercritical CO2 meets the hopefully immovable object of a clay-rich capping formation? Well, this is geology, so the answer is: "It depends on a bunch of details." Swelling clays could shrink or swell, depending on their interlayer cations, hydration state, and probably their framework composition too…or the carbon dioxide and water molecules could swap places without much volume change at all. It's an important question, and experiments to address it have really only been undertaken in the last five years.
- At Southern Illinois University, I finally got to fulfill a life-long ambition (as a lover of all things Hawaiian) to study mafic rocks. They just happened to be mafic rocks from another planet. A few Martian meteorites contain a few microscopic grains of amphibole minerals, and these are unbelievably precious because amphibole has a site to house not only OH, but also F and Cl. We know on Earth that OH content of a magma source region is crucial for fluxing melting, and the same is likely true for Mars. What is much less well-studied are the effects of those other two components, which not only flux melting but also play favorites with ferromagnesian minerals—F encourages Mg to stay in the melt, while Cl complexes with Fe, and this can cause olivine to crystallize instead of pyroxene or vice-versa in mafic systems. After sailing the seven seas of literature, I ransacked several models and put together a composite model to describe how amphibole partitions OH from Cl in mafic melts. What's really needed, instead of piracy, is a dedicated program to gather analytical data and build not only a better model for Cl, but a model for F as well, and then to face the even more daunting task of considering how amphibole raids fluids for its essential monovalent anion nutrients. (The most Cl-rich amphibole known to science, with one or two possible exceptions, comes from Mars and was probably put there by a fluid so rich in Fe and Cl that it may have been practically a molten salt.) Along the way, several more insights about amphibole and melt thermodynamics are liable to fall out as extra booty.
Ph.D., Geological Sciences
- University of Notre Dame, August 2002 to May 2006
Arthur J. Schmitt Fellow
Dissertation: crystal, environmental, and complexation chemistry of oxidized uranium
A.M., Earth and Planetary >Science
- Washington University in St. Louis, June 2001 to July 2002
Thesis: infrared and Raman spectroscopy of majoritic garnet
B.A., Earth and Planetary Science Classics
- Washington University in St. Louis, August 1997 to May 2001
Ernest L. Ohle Award
Honors thesis (EPSc): infrared spectroscopy and thermal conductivity of garnets
- Indiana Licensed Professional Geologist #2307
- Mineralogical Society of America
- Geological Society of America
- American Geophysical Union
- Giesting, PA, and Filiberto, J. Amphibole chemistry and the formation environment of potassic-chloro-hastingsite in the nakhlites MIL 03346 and pairs and NWA 5790. Submitted to Meteoritics & Planetary Science.
- Giesting, PA, Filiberto, J, et al., 2015. Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes. Meteoritics & Planetary Science, v. 50, p. 433-460, doi:10.1111/maps.12430.
- Giesting, PA, Filiberto, J, 2014. Quantitative models linking igneous amphibole composition with magma Cl and OH content. American Mineralogist, v. 99, p. 852-865, doi:10.2138/am.2014.4623.
- Filiberto, J, Treiman, AH, Giesting, PA, Goodrich, CA, Gross, J, 2014. High-termperature chlorine-rich fluid in the martian crust: A precursor to habitability. Earth and Planetary Science Letters, v. 401, p. 110-115, doi:10.1016/j.epsl.2014.06.003.
- Giesting, PA, Hofmeister, AM, Wopenka, B, Gwanmesia, GD, Jolliff, BL, 2004. Thermal conductivity and thermodynamics of majoritic garnets: implications for the transition zone. Earth and Planetary Science Letters, v. 218, p. 45-56.
- Hofmeister, AM, Giesting, PA, Wopenka, B, Gwanmesia, GD, Jolliff, BL, 2004. Vibrational spectroscopy of pyrope-majorite garnets: structural implications. American Mineralogist, v. 89, p. 132-146.
- Giesting, PA, Hofmeister, AM, 2002. Thermal conductivity of disordered garnets from infrared spectroscopy. Physical Review B, v. 65, 144305.
Environmental mineralogy/geochemistry/energy resources
- Giesting, PA, Guggenheim, S, Koster van Groos, AF, and Busch, A, 2012. X-ray diffraction study of K- and Ca-exchanged montmorillonites in CO2 atmospheres. Environmental Science & Technology, v. 46, p. 5623-5630.
- Giesting, PA, Guggenheim, S, Koster van Groos, AF, 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, v. 8, p. 73-81.
- Giesting, PA, Burns, PC, 2006. Uranyl-organic complexes: structure symbols, classification of carboxylates, and uranyl polyhedral geometries. Crystallography Reviews, v. 12, p. 205-255.
- Giesting, PA, Porter, NJ, Burns, PC, 2006. A series of sheet-structured alkali metal uranyl oxalate hydrates: structures and IR spectra. Zeitschrift fur Kristallographie, v. 221, p. 589-599.
- Giesting, PA, Porter, NJ, Burns, PC, 2006. Uranyl oxalate hydrates: structures and IR spectra. Zeitschrift fur Kristallographie, v. 221, p. 252-259.
Amphibole and Halogens
In Giesting & Filiberto (2014), we showed the ability to model the partitioning of OH and Cl between amphibole and a coexisting melt using existing models for amphibole redox and existing data. This was meant as a proof of concept rather than a finished model.
To get reliable models for the competitive interchange of F, Cl, and OH between amphibole and melt, we need more and better data on synthetic and well-characterized natural samples:
- Syntheses will be needed to reach the un-Earthly Fe-rich chemistry of Martian melts and adequately explore compositional space to develop a robust model.
- Natural samples with coexisting melt glass and amphibole can also be used if reliable values can be found for equilibrium temperature, pressure, and oxygen fugacity.
- Synthetic and natural samples will need amphibole and glass analyzed carefully for both cations and halogens. Analyzing for F is not easy on the electron microprobe, and caution is also needed for Na and K.
- OH content of amphibole will need to be estimated or analyzed. So far as I know, this will require an ion microprobe.
- OH content of coexisting glass can be measured by IR. It would be desirable to run some ion microprobe analyses to check the IR results.
- Fe3+ content of amphibole is needed for an unambiguous determination of the chemical formula. Determination of Fe3+ from EMP data is an evergreen goal, and recent work (Lamb et al. 2012, Am Min, 97:951) contains a calibration for amphibole.
With a suitably large and reliable dataset, the following would be possible:
- Check the Popp et al. (2006, Am Min, 91:54) model for amphibole redox (Fe & H) for more amphibole chemistries and create a more robust calibration.
- Calibrate an IR (or Raman) method for determining OH in amphibole.
- Check and recalibrate models for IR determination of OH in glass, especially for Martian compositions.
- The crown jewels: Calibrate models for both F and Cl partitioning between melt and amphibole.
- Consider the thermodynamic implications of our data, like finding enthalpies and free energies of exchange for the OH-Cl, OH-F, and F-Cl pairs in amphibole.
Conduct chemical modeling and compare the results, leading to a deeper theoretical understanding of the physical chemistry of the O(3) site in amphibole.
Kaua'i is a mysterious and beautiful island. Second-oldest of the Hawai'ian Islands with any substantial amount of land area still above sea level, it has the largest amount of alkaline, post-erosional volcanic rock exposed at the surface.
Kaua'i is either the fourth or fifth most studied of the islands, with Hawai'i itself, O'ahu, and Maui definitely out in front and maybe Moloka'i as well. Kaua'i's history, longer than that of the other islands, is also more complex. It suffered a number of episodes of slumping, like the massive event that formed O'ahu's Pali, but the geologic results are less clear. To this day the actual location of Kaua'i's caldera is not conclusively proven, despite years of field mapping and geophysical surveys. It's not out of the question that Kaua'i was once a volcanic doublet like O'ahu, Moloka'i, or Maui, but the conventional view that it was just one large volcano still holds definite sway. Kaua'i is one of the wettest places on Earth, and that makes getting pristine samples of Kaua'i rock for analysis a real pain. For the same reason, Kaua'i is of course heavily eroded, and samples of the late siliceous cap are scanty and took a long time to find.
At present, I have some samples from Kaua'i that need a basic petrographic interpretation and to be related to existing geological maps and classifications. I am looking for an undergrad who has taken igneous petrology to help me with this work (although I would hardly turn away a grad student).
In the longer term, I would like to tackle some bigger picture questions by getting a better grasp of the individual histories of the collapse structures in terms of both faulting and petrology of the infilling lavas. This will require developing one or more collaborations with geophysicists or geodynamicists. Kaua'i represents a great target for a seismic survey to corroborate, correct, and transcend the results of the gravity survey of Flinders et al. (2010), which had maddeningly poor coverage in the critical central portion of the island. The fascinating geodynamics work of Bianco et al. (2005), which suggested that passage through the flexural bulge(s) of later-built islands was the cause of rejuvenated period volcanism, could use a considerable amount of extension in terms of realism, since the flexure model presented in the paper consisted of an analytic solution to the response of an elastic plate to a point load. Garcia et al. (2010) show that this model is, unsurprisingly, not accurate in its ability to predict the timing or volume of rejuvenated series volcanism on Kaua'i; it badly underestimates the onset time, time of peak volcanism, flux rate, and quantity of volcanism. It remains to be seen if a numeric model that takes the entire archipelago into account could produce results that better match observations. As Bianco et al. (2005) showed, there are a number of petrologic indicators (including major elements, Sr, and Nd isotopes) that are predicted by the model, making this project a great opportunity for interdisciplinary research.
Clay mineralogy and carbon sequestration
In the long term, I look to build a program of study focusing on the behavior of clay minerals at subsurface conditions, including the conditions of caprocks for oil and gas reservoirs as well as proposed carbon sequestration reservoirs. Initial studies of this behavior have shown swelling of partially hydrated smectites at moderate pressures and temperatures, where dehydration of the clay was considered more likely. This result shows how little our expectations for this system may match reality at other conditions. Additional studies in this field are primarily either computational or ex situ, and while computational studies have been able to describe the in situ experimental work ad hoc, they were unable to predict it. Ex situ studies are not of much value to study smectite-CO2 behavior since the swelling behavior is dominantly reversible.
I have also worked with the clay-CH4 system. Evidence from studies at UIC suggests that a clathrate-like structure intercalates into smectite under conditions near the stability of bulk clathrate, but nothing is known about its kinetic behavior, the relative size of the bulk and clay-hosted reservoirs, and therefore the possible importance of this phase to methane cycling. Other important volatile phases, like H2S, may also intercalate into clay at high-pressure conditions, but the experiments have never been performed.
Based on my previous experience at the University of Illinois-Chicago, I hope eventually to construct an environmental chamber capable of sustaining mineral-brine-gas mixtures at reservoir conditions for lengthy periods and allowing in situ examination of the contents via X-ray diffraction, Raman spectroscopy, and other techniques. This would allow study of both the surface wetting behavior of fluids on minerals (a lively topic of research) and the bulk behavior of changeable phases such as clays and zeolites (much less studied to date). This chamber could be applied to studies ranging from the effect of volatile compounds on clay structure in oil, gas, and sequestration reservoirs to conditions during argillic alteration in hydrothermal systems, to the behavior of ocean bottom muds in contact with methane, carbon dioxide, and other volatiles. This would open up wide fields of study in pure and applied clay mineralogy, many of which are directly linked with greenhouse gases and climate change. Understanding clays and their behavior under different gases is valuable in a wide variety of geological, chemical, oceanographic, and engineering fields. The environmental chamber would be a resource for UTK faculty in marine and planetary science in particular to study the behavior of materials and systems at nonambient conditions relevant to terrestrial and extraterrestrial oceans and aquifers.
Clay minerals and contaminants
An issue that has bothered me since the three years I worked at IDEM in Indianapolis has been the very simplistic way in which a soil's ability to sorb contaminants was calculated, based pretty much solely on organic carbon content. This was after I had been in graduate school at Notre Dame, where many of my peers were working on projects dealing with mineral surfaces and metal complexation. It's probably high time to 1) assess where the state of the art currently is for regulatory agencies across the country and world regarding both organic and metals contaminant sorption models, 2) survey the literature and identify places where solid insights need to be brought across the divide from theory to practice, and 3) target remaining gaps in knowledge with an eye to creating models that are simple enough for consultants to use and regulators to interpret in a timely way.
The department possesses a Rigaku Ultima IV, a workhorse theta-theta style powder diffractometer. Purchased in 2011, it comes with a selection of sample mounts and modern software for data interpretation.
X-ray diffraction is a century-old analytical technique, which means that modern instruments contain 100 years' worth of streamlining and optimization. The XRD is a simple instrument that still provides invaluable information about geological materials. We use it in Mineralogy (GEOL 310) as an accessible example of analytical instrument, so student use of the XRD is possible and welcomed with some essential safety training.
Below are some data derived from a Costa Rica basalt collected in the late 1990s. The PDXL software has identified a midrange plagioclase ("calcian albite") and augite pyroxene as the two dominant minerals in this specimen. On the left, the peak locations for the two minerals identified are shown below the raw diffraction pattern. By comparing magnitudes of the dominant diffraction peaks in the pattern, the software has generated an estimate of the quantity of each. We also have the capability to use a much more sophisticated treatment called Rietveld refinement to model the diffraction pattern if the data and problem to be solved warrant.