1. Department of Geological Sciences, The University of Texas at El Paso, El Paso, Texas 79968, U.S.A.
2. Virginia Tech National Center for Earth and Environmental Nanotechnology (NanoEarth), Blacksburg, Virginia 24061, U.S.A.
3. † Present address: Oceanography Department, Texas A&M University, College Station, TX 77845, U.S.A.
4. Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, U.S.A.
5. Department of Material Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061, U.S.A.