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What is an Electron Microprobe?

Electron microprobes are analytical instruments that can image and analyze materials that we are unable to see/do using an optical microscope. These machines can also identify elements present in a mineral as small as 5 thousands of a millimeter with a small degree of error. Electron microprobe analysis is non-destructive and is used for detailed analytical study of important features in rocks, including compositional zoning of individual grains or reaction zones between grains.

Oklahoma State University currently maintains a Transmission Electron Microprobe, Confocal Microscope and Scanning Electron Microscope (SEM). The SEM is used primarily for imaging (taking pictures of) samples. If the instrument could be fitted with analytical equipment so that quantitative chemical analyses of minerals/materials could be made, we would call it an analytical SEM or electron microprobe.

SEMs and electron microprobes are valuable pieces of scientific instrumentation, but do have limits. Not all materials can be exposed to the high vacuum required by the machine and elements lighter than atomic number 8 (oxygen) cannot be measured without reservations. Many elements cannot be measured at all if they are present below 100 parts per million. Still, this machine has proved valuable to mineralogists and petrologists, and a good operator can vary one parameter or another to circumvent instrumental weaknesses.