New Mexico Mineral Symposium — Abstracts

The electron microprobe x-ray analyzer has become an important tool in the study of minerals. This talk describes the-instrument and the types of data that can be obtained from it. Examples of data obtained on New Mexico minerals will be used to illustrate and explain the various functions of the probe and to show why this instrument has become almost indispensable for the study of minerals.
Like a scanning electron microscope, the probe can produce secondary electron images that allow us to look at the morphological details of minute crystals and aggregates and their surfaces. Because of the large depth of field, these images are much sharper than those obtained from optical microscopes and, because of the shorter wavelengths of electrons, the magnification can be much greater. Unfortunately, the images are only available in black and white.

Both machines can also produce images from back-scattered electrons, images that tell us something about the composition of the minerals examined. Minerals with higher atomic-number elements show up brighter than the other minerals with which they are associated. This is something no optical microscope can do.

By far the most important function of the probe is analyzing the x-rays given off by a material and thereby determining quali¬tatively and/or quantitatively which elements are present. When a material is bombarded by electrons, x-rays are produced that are characteristic of the elements present. Determining the energy (or wavelength) of the x-ray peaks tells us which elements are there. By comparing the intensity of the x-rays from the sample with those from suitable standards, the probe can give us very good quantitative analyses of very small volumes. Alternatively, the probe can scan the beam over an area and produce an x-ray map showing how an element is distributed on our sample.

*This work was performed at Sandia National Laboratories and was supported by the U.S. Department of Energy under Contract #DE-AC04-76DP00789.