Microanalyses by electrons: The ultimate alchemist (GC-09)
Chemical analyses of geologic materials have always played a large role in geologic study. In the past, analyses required large amounts of material, but the chemistry of such small but important geologic materials as minerals filling pore spaces or fine-grained ore minerals was poorly known.

A tool developed since the 1950's, the electron microprobe analyzer, allows geologists to determine chemical compositions of particles only a few micrometers (.001 millimeter) in size. In this instrument a bean of electrons at high voltage is focused on the specimen by electromagnetic lenses. The electron bean causes the sample to emit X-rays with characteristics that depend on the chemistry of the sample. Each chemical element emits X-rays of a unique kind. By comparing the kinds and amounts of radiation with those of well-known standard materials, the elements and their amounts in the sample can be calculated.

Our Hoosier State Beneath Us: Geochemistry/Geophysics