PHASE ANALYSIS USING BACKSCATTERED ELECTRON IMAGING STUDY OF NEW MILLER RANGE NAKHLITES

 

Andrew R. Konicek1, Nicole Lunning2, Cari M. Corrigan2, and Edward P. Vicenzi1,3

 

1Surface and Microanalysis Science, National Institute of Standards and Technology, Gaithersburg, MD

2Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C.

3Museum Conservation Institute, Smithsonian Institution, Suitland, MD

 

The intensity of backscattered electrons (BSE) produced while imaging a sample with scanning electron microscopy (SEM) provides information about the average atomic number of the area being imaged, and therefore information about the chemical composition. We have developed a new automated routine to analyze the grayscale intensity histogram created from BSE images in order to perform a fast, high‑resolution phase analysis of the sample. Gaussian peaks are fit to features in the histogram to determine phases, and then these phases are traced back to false‑color the image. BSE imaging provides a faster and higher-resolution compositional analysis than slower spectroscopic methods, such as energy dispersive spectroscopy (EDS). Also, most SEMs are equipped with the ability to collect BSE images, while not all have EDS systems. Samples to demonstrate this new phase analysis method were selected from Martian meteorites found in the Antarctic Miller Range. Samples from meteorites collected in 2003 were compared with samples collected in 2009 to determine the relative phase abundance of pyroxene and olivine components. The results suggest that, based on similar relative concentrations of each component, the meteorites collected at different times do indeed come from the same location on Mars.