One of the first samples analyzed by Castaing in his electron probe microanalyzer (EPMA) some 50 years ago was an iron meteorite. The Widmanstatten pattern microstructure of iron meteorites can be observed at very low magnifications ( Fig. 1). These meteorites are ideal samples for microanalysis because of the Ni gradient which extends over 10 to 1000 microns in the parent taenite phase of these Fe-Ni samples (Fig. 3). The Ni gradient is the result of very slow cooling of the iron meteorite, in terms of millions of years, within a parent'asteroid.

The scanning electron microscope (SEM) has been used to characterize the microstructure of meteorites, as well as samples from the moon and mars. For example, the microstructure of the dark etching taenite areas (T in Fig. 1) of the Carleton iron meteorite is shown in Fig 2. In this example, precipitates are observed along original martensite laths which form during the cooling of the iron meteorite at low temperatures.