TY - JOUR
T1 - Thermal emission spectroscopy of microcrystalline sedimentary phases
T2 - Effects of natural surface roughness on spectral feature shape
AU - Hardgrove, Craig
AU - Rogers, A. D.
AU - Glotch, T. D.
AU - Arnold, J. A.
N1 - Funding Information:
We thank Troy Rasbury and Cara Thompson for contributing samples and petrographic facilities for this work. Stacey Sullivan kindly acquired the Zygo measurements. This work was supported by the NASA Mars Fundamental Research Program under grant NNX09AL22G to A.D.R. and the RIS4E node of the NASA Solar System Exploration Research Virtual Institute (SSERVI). This is SSERVI publication number SSERVI-2015-235. The data presented in this paper are available in the supporting information and, upon acceptance of this paper for publication, all spectra and roughness data will be made available at http://aram.ess.stonybrook. edu/drogers/data-products.htm
Publisher Copyright:
©2016. American Geophysical Union. All Rights Reserved.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - Distinguishing between microcrystalline and macrocrystalline mineral phases can help constrain the conditions under which those minerals formed or the degree of postdepositional alteration. This study demonstrates the effects of crystal size and surface roughness on thermal infrared emission spectra of micro and macrocrystalline phases of the two most common minerals on Earth, quartz and calcite. Given the characteristic depositional and environmental conditions under which microcrystalline minerals form, and the recent observations of high-silica deposits on Mars, it is important to understand how these unique materials can be identified using remote infrared spectroscopy techniques. We find that (a) microcrystalline minerals exhibit naturally rough surfaces compared to their macrocrystalline counterparts at the 10 μm scale; and that (b) this roughness causes distinct spectral differences within the Reststrahlen bands of each mineral. These spectral differences occur for surfaces that are rough on the wavelength scale, where the absorption coefficient (k) is large. Specifically, the wavelength positions of the Reststrahlen features for microcrystalline phases are narrowed and shifted compared to macrocrystalline counterparts. The spectral shape differences are small enough that the composition of the material is still recognizable, but large enough such that a roughness effect could be detected. Petrographic and topographic analyses of microcrystalline samples suggest a relationship between crystal size and surface roughness. Together, these observations suggest it may be possible to make general inferences about microcrystallinity from the thermal infrared spectral character of samples, which could aid in reconstructions of sedimentary rock diagenesis where corresponding petrographic or microimaging is not available.
AB - Distinguishing between microcrystalline and macrocrystalline mineral phases can help constrain the conditions under which those minerals formed or the degree of postdepositional alteration. This study demonstrates the effects of crystal size and surface roughness on thermal infrared emission spectra of micro and macrocrystalline phases of the two most common minerals on Earth, quartz and calcite. Given the characteristic depositional and environmental conditions under which microcrystalline minerals form, and the recent observations of high-silica deposits on Mars, it is important to understand how these unique materials can be identified using remote infrared spectroscopy techniques. We find that (a) microcrystalline minerals exhibit naturally rough surfaces compared to their macrocrystalline counterparts at the 10 μm scale; and that (b) this roughness causes distinct spectral differences within the Reststrahlen bands of each mineral. These spectral differences occur for surfaces that are rough on the wavelength scale, where the absorption coefficient (k) is large. Specifically, the wavelength positions of the Reststrahlen features for microcrystalline phases are narrowed and shifted compared to macrocrystalline counterparts. The spectral shape differences are small enough that the composition of the material is still recognizable, but large enough such that a roughness effect could be detected. Petrographic and topographic analyses of microcrystalline samples suggest a relationship between crystal size and surface roughness. Together, these observations suggest it may be possible to make general inferences about microcrystallinity from the thermal infrared spectral character of samples, which could aid in reconstructions of sedimentary rock diagenesis where corresponding petrographic or microimaging is not available.
KW - chert
KW - micrite
KW - microcrystalline spectroscopy
KW - surface roughness
KW - surface roughness thermal emission spectra
KW - thermal emission spectroscopy
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U2 - 10.1002/2015JE004919
DO - 10.1002/2015JE004919
M3 - Article
AN - SCOPUS:84962858111
VL - 121
SP - 542
EP - 555
JO - Journal of Geophysical Research: Planets
JF - Journal of Geophysical Research: Planets
SN - 2169-9097
IS - 3
ER -