Office: 207 Parkinson Lab
My research program attempts to answer fundamental questions about how minerals form, and why particular crystal structures are stable at a particular set of conditions. I have worked on a variety of systems at both low and high temperatures, but my work is united by a desire to understand the fundamental thermodynamics and kinetics that make possible the enormous variety of crystalline materials we see on our planet. Here is a summary of current projects:
1) Predicting and finding new mineral species
I am the principle investigator of a unique, worldwide effort called the Carbon Mineral Challenge. Using statistical methods, my colleagues and I have predicted the existence of ~146 undiscovered carbon-bearing minerals, as well as what sort of chemistry they have, and in what geologic environments we should look for them. I’ve formed a coalition of mineralogists around the world to assist in the search, and we’re hoping to discover as many new minerals with the crucial element carbon as possible.
2) Modeling mineral compression and phase stability
I am developing a model that accounts for the compressibility of minerals by considering the structure as a collection of independent, compressible ions. Each type of ion compresses to a different extent, resulting in the overall compressibility of the mineral. Because the radius ratio is allowed to change as a function of pressure, the model can also be used to predict the pressures at which crucial phase transitions will occur, making possible the theoretical prediction of phase stability. I am working to further test and develop this model using high-pressure X-ray diffraction experiments on halide and oxide minerals.
3) Modeling reactions between minerals and the fluids that form them
Many minerals crystallize from parent fluids within the Earth, so understanding how these reactions happen, and at what rate they happen, is crucial to understanding mineral formation. I have developed a kinetic modeling program called “MinKin” (for Mineral Kinetics) that is capable of fitting experimental data from complex systems (in which multiple minerals can precipitate, dissolve, and transform), and extracting information about which reactions are occurring and at what rates. Working with collaborators at Penn State, Oak Ridge National Lab, and Brookhaven National Lab, I have so far conducted experiments on the crystallization of Ti and Al oxide minerals from aqueous fluids. By measuring the changing amounts of minerals in these time-resolved experiments and analyzing the data with MinKin, we are gaining more detailed information than previously possible about which chemical processes are responsible for mineral formation, even in the complex systems we find in nature.
4) Using mineral occurrence to document Earth’s changing chemistry
I am working with collaborators at the Carnegie Institution, Johns Hopkins, Rensselaer Polytechnic Institute, and the University of Arizona to use large databases of worldwide mineral occurrences to track changes in redox conditions through geologic time. Events such as the “Great Oxidation Event” oxidized many transition metals present in Earth’s crust, making possible entirely new sets of minerals. By examining the occurrence of Mn minerals through time, in which Mn can exist in the +2, +3, and +4 oxidation states, I found that the average oxidation state of Mn in mineral deposits mirrored the rise of oxygen in Earth’s atmosphere during the phanerozoic. We are currently using data for minerals of other transition elements to gain a more detailed picture of how the oxidation state of Earth’s crust changed over time, and when the formation of new sets of minerals fundamentally changed Earth’s composition.
Hazen, R.M.; Hystad, G.; Golden, J.J.; Hummer, D.R.; Liu, C.; Downs, R.T.; Morrison, S.M.; Grew, E.S. (2016) Cobalt mineral ecology. American Mineralogist, in press.
Hummer, D.R.; Noll, B.; Hazen, R.M.; Downs, R.T. (2016) Crystal structure of abelsonite, the only known crystalline geoporphyrin. American Mineralogist, submitted.
Hazen, R.M.; Hummer, D.R.; Hystad, G.; Downs, R.T.; Golden, J.J. (2016) Carbon mineral ecology: predicting the undiscovered minerals of carbon. American Mineralogist 101, 889-906.
Bower, D.M.; Hummer, D.R.; Steele, A.; Kyono, A. (2015) The co-evolution of Fe-oxides, Ti-oxides, and other microbially induced mineral precipitates in sandy sediments: Understanding the role of cyanobacteria in weathering and early diagenesis. Journal of Sedimentary Research 85, 1213-1227.
Hummer, D.R.; Heaney, P.J. (2015) MinKin: A kinetic modeling program for the precipitation, dissolution, and phase transformation of minerals in aqueous solution. Chemical Geology 405, 112-122.
Kono, Y.; Kenney-Benson, C.; Hummer, D.R.; Ohfuji, H.; Park, C.; Shen, G.; Wang, Y.; Kavner, A.; Manning, C.E. (2014) Ultralow viscosity of carbonate melts at high pressures. Nature Communications 5:5091 doi: 10.1038/ncomms6091.
Hummer, D.R.; Kubicki, J.D.; Kent, P.R.C.; Heaney, P.J. (2013) Single-site and monolayer surface hydration energy of anatase and rutile nanoparticles using density functional theory. Journal of Physical Chemistry C 117, 26084-26090.
Seagle, C.T.; Cottrell, E.; Fei, Y.; Hummer, D.R.; Prakapenka, V.B. (2013) Electrical and thermal transport properties of iron and iron-silicon alloy at high pressure. Geophysical Research Letters 40, 5377-5381.
Lee, N.; Hummer, D.R.; Sverjinsky, D.A.; Rajh, T.; Hazen, R.M.; Steele, A.; Cody, G.D. (2012) Speciation of L-DOPA on nanorutile as a function of pH and surface coverage using surface-enhanced Raman spectroscopy (SERS). Langmuir 28(50), 17322-17330.
Hummer, D.R.; Heaney, P.J.; Post, J.E. (2012) In situ observations of particle size evolution during hydrothermal crystallization of TiO2: A time-resolved synchrotron SAXS and WAXS study. Journal of Crystal Growth 344(1), 51-58.
Hummer, D.R.; Fei, Y. (2012) Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite. American Mineralogist 97, 1915-1921.
Hummer, D.R.; Kubicki, J.D.; Kent, P.R.C.; Post, J.E.; Heaney, P.J. (2009) The origin of nanoscale stability reversals in titanium oxide polymorphs. Journal of Physical Chemistry C 113(11), 4240-4245.
Hummer, D.R.; Heaney, P.J.; Post, J.E. (2007) Thermal expansion of anatase and rutile between 300 and 575 K using synchrotron powder X-ray diffraction. Powder Diffraction 22(4), 352-357.
GEOL 310 - Mineralogy
GEOL 419 - Ore Deposits