Effects of small crystallite size on the thermal infrared (vibrational) spectra of minerals

1Victoria E. Hamilton,2Christopher W. Haberle,3,4Thomas G. Mayerhöfer
American Mineralogist 105, 1756–1760 Link to Article [http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1756.pdf]
1Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, no. 300, Boulder, Colorado 80302, U.S.A 2School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, U.S.A.
3Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, D-07745 Jena, Germany 4
4Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University, Helmholtzweg 4, D-07743 Jena, Germany
Copyright: The Mineralogical Society of America

The thermal infrared (TIR, or vibrational) emission spectra of a suite of synthetic Mg-Fe olivines exhibit notable differences from their natural igneous counterparts in terms of their band shapes, relative depths, and reduced shifts in some band positions with Mg-Fe solid solution. Comparable reflectance spectra acquired from olivine-dominated matrices and fusion crusts of some carbonaceous chondrite meteorites exhibit similar deviations. Here we show that these unusual spectral characteristics are consistent with crystallite sizes much smaller than the resolution limit of infrared light. We hypothesize that these small crystallites denote abbreviated crystal growth and also may be linked to the size of nucleation sites. Other silicates and non-silicates, such as carbonates, exhibit similar spectral behaviors. Because the spectra of mineral separates are commonly used in the modeling and analysis of comparable bulk rock, meteorite, and remote sensing data, understanding these spectral variations is important to correctly identifying the
minerals and interpreting the origin and/or secondary processing histories of natural materials.


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