Cathodoluminescence (CL -light emission stimulated by electron bombardment) of quartz has various
causes. The emissions produced by the defects are easily determined but the actual causes much less so. Individual CL scans used a MonoCL3 system attached to a JEOL 820 scanning electron microscope gave spectra over the 300 to 800 nm range. The resulting experimental plot was fitted with three unconstrained Gaussian components using Origin 7.5. Each scan produced red and violet emission bands together with either a blue or yellow or orange emission band: these were called mid-range colours. The aim was to compare the variation in the percentage relative intensity of the three emission bands (violet: mid-range colour: red) in a collection of agates from Fairburn, S Dakota, USA.
As there are only three components, the relationship can be demonstrated using a ternary plot, as shown here.
Note: Origin assumes that each row of X, Y, and Z values (i.e. each of the three fractions you are analyzing) are normalized so that X+Y+Z = 1. If your data are not normalized, Origin will do this for you.
Terry Moxon has been interested in the problems of agate genesis for the past 30 years. He is presently funded by The Leverhulme Trust as a research visitor at the Dept. of Earth Sciences, University of Cambridge, England. The present work is characterising agates and studying agate growth.
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