1. Institute of Geosciences and Geography, Mineralogy/Geochemistry, Martin Luther University Halle-Wittenberg, 06120 Halle, Germany
2. Nanomechanics, Inc., 105 Meco Lane, Oak Ridge, Tennessee 37830-7263, USA
3. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305-4034, USA
4. Department of Geological Sciences and Center for International Security and Cooperation, Stanford University, Stanford, California 94305-2115, USA