An Electron Microprobe, also called an electron probe micro-analyzer (EPMA), is an electron beam instrument used primarily for the in situ non-destructive chemical analysis of inorganic solid samples. It is fundamentally the same as the more common Scanning Electron Microscope (SEM), but the primary importance of an EPMA is the ability to acquire precise, quantitative elemental analyses at very small "spot" sizes (as little as 1-2 microns diameter), primarily by wavelength-dispersive spectroscopy (WDS). The electron optics of an SEM or EPMA allow much higher resolution images to be obtained than can be seen using visible-light optics, so features that are irresolvable under a light microscope can be readily imaged and then used to study detailed microtextures or provide the fine-scale context of an individual chemical spot analysis. 

 

The electron microprobe is the main-stay of igneous and metamorphic petrologists, or at least it should be.

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