Quantitative Analysis
The electron microprobe is mostly used for WDS and EDS quantitative analysis of major and minor elements of minerals and glasses. Volumes as small as 1 micron (10E-6 m) diameter can be analyzed. Occasionally museum specimens from other departments or from other museums are analyzed. In the order of 10,000 quantitative analyses are performed per year. A large proportion of the analyses are performed on minerals and glasses from volcanic rocks.
The electron microprobe at the Department of Mineral Sciences has played a very important role in the construction of the Smithsonian Abyssal Volcanic Glass Data File (AVGDF). During the past 10 years over 9,000 analyses of volcanic glasses from ocean floor basalts from all over the world were performed in our laboratory. This map shows the sample localities.
The data serve to model processes associated with magma generation and fractionation in the asthenosphere and lithosphere beneath seafloor spreading centers.
Map and diagrams are extracted from Melson,W.G, O’Hearn,T. and Jarosewich, E., 2002. A data brief on the Smithsonian Abyssal Volcanic Glass Data File. Geochemistry Geophysics Geosystems, Vol. 3 No. 4, 10. http://www.agu.org/journals/gc/gc0204/2001GC000249/
The electron microprobe is extensively used for the analysis of minerals also. The following diagrams are part of the crystal chemistry study of the substitution of Sc in Nb-Ta oxides.
Correlation of Sc with (a) Ta, and (b) Sn fractionation in Nb-Ta oxide minerals. Circles - columbite, squares - stannian ixiolite, triangles - titanian ixiolite, dots - wolframian ixiolite, diamonds - scandian ixiolite. Black field in B represents data for columbite and stannian and titanian ixiolites. This is part of the crystal chemistry study of the substitution of Sc in Nb-Ta oxides.
Wise, M.A., Cerny, P. and Falster, A.U., 1998 Scandium substitution in columbite-group minerals and axiolite. The Canadian Mineralogist, vol. 36, pp. 673-680.
Quantitative WDS analyses of areas of 100 x 100 micrometers. This diagram shows the comparisonof lithics (tools) from early humans with outcrops in the Olorgesaille site, Kenya. Olorgesaille is located 100 km SW of Nairobi. The presence of early humans in this site dates to 350,000 years ago. A special focus of the Humans origins program at the Smithsonian is the intricate interplay of early human populations and the environments in which they lived.