MicroAnalysis Page

What is Microanalysis?

Microanalysis is the compositional characterization of small volumes of solid material. This may involve determinations of either chemical or isotopic compositions (or both), as well as other parameters such as the local redox state and valence of specific ions etc. Depending on the technique and application such analyses are made at scales ranging from a few hundred microns down to less than one micron.

Microanalysis can be useful in a number of situations. These include:

1. Analysis of very small and chemically-distinct domains located within other materials. Geological examples include small mineral or melt inclusions commonly found trapped within larger crystals in many igneous rocks. Another good example is the primordia of otoliths - the small central portion of the otolith (fish ear bone) that grows while the fish still receives its nutrient supply from the egg.

2. Provision of chemical or isotopic information within a textural framework. Many materials show complex textures reflecting different 3D distributions of various chemical components. In fields such as igneous petrology the examination of such textures by microscopy has long been a mainstay. Microanalysis provides compositional information to complement and quantify observations on textural observations.

3. Rapid analysis of homogeneous solids. In many cases microanalysis techniques also provide an efficient means to characterize homogenous materials. Many microanalysis techniques are relatively rapid and require less sample preparation than bulk analysis techniques. Microanalysis also provides a test of whether a 'homogenous' material is truly homogeneous at the microscale.

How do you do it?

Microanalysis may be performed by physically collecting very small samples using a micromilling or microdrilling machines, or more commonly by using microbeam techniques to collect the information. These techniques use finely focused beams of ions, photons, electrons, protons or X-rays that physically interact with the material to be analyzed. The nature of the interaction, and/or the solid or electromagnetic products produced by the interactions can then be used to characterize the material of interest.

There are many different microanalytical techniques out there, and there are even more applications. The following discussion is aimed at techniques that are commonly used (at least by me!) in the earth and environmental sciences.