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Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron TomographyWe report here the crystal morphologies of MV-1 and ALH84001 magnetites as calculated by back-projection using electron tomography. In the present study, we used a 300 keV TEM with a field emission gun (Tecnai F-30 from FEI Inc.), equipped with a 2048 x 2048 pixel CCD camera from Gatan Inc. to image magnetite crystals over tilt ranges of approx. +/- 72 deg in 2 deg tilt intervals. The images were aligned for back-projection, either manually, or through the use of fiducial 5 nm Au spheres affixed to the specimen prior to microscopy. Three-dimensional (3-D) reconstructions were computed using weighted back-projection of the tilted views. The tomograms were viewed and analyzed as a series of slices 1.0 nm thick, taken parallel to the specimen-supporting grid, using the IMOD software package. The shape of each magnetite crystal was determined by defining the external contour of a given magnetite in each slice and assembling a stack of these contours in 3-D. To aid in visualization, the stacked contour array was reduced to an optimal mesh by Delaunay triangulation. The surface normal to each of the triangles in the mesh was calculated and the triangle faces colored according to the orientation of that surface normal relative to the principal crystallographic axis of magnetite. Green surfaces correspond to {111} orientations, blue surfaces to {100} orientations, and red surfaces to {110} orientations. Triangles whose surface normal did not correspond to one of the principal axes were colored gray. Within the experimental and numerical uncertainties of the deconvolution, the tomographic reconstruction of both MV-1 and ALH84001 magnetites are equivalent and correspond to a truncated hexa-octahedral morphology.
Document ID
20030111558
Document Type
Conference Paper
Authors
Thomas-Keprta, Kathie L. (Lockheed Martin Space Operations Houston, TX, United States)
Clemett, Simon J. (Lockheed Martin Space Operations Houston, TX, United States)
Shimmin, Joel (Colorado Univ. Boulder, CO, United States)
Morphew, Mary (Colorado Univ. Boulder, CO, United States)
McIntosh, J. Richard (Colorado Univ. Boulder, CO, United States)
Bazylinski, Dennis A. (Iowa State Univ. of Science and Technology Ames, IA, United States)
Kirschvink, Joseph L. (California Inst. of Tech. Pasadena, CA, United States)
Wentworth, Susan J. (Lockheed Martin Space Operations Houston, TX, United States)
McKay, David S. (NASA Johnson Space Center Houston, TX, United States)
Vali, Hojatollah (McGill Univ. Montreal, Quebec, Canada)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Publication Information
Publication: Lunar and Planetary Science XXXIV
Subject Category
Geosciences (General)
Report/Patent Number
JSC-CN-7994
Distribution Limits
Public
Copyright
Public Use Permitted.

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