Monday, September 14, 2009

Rock Photography Part III: Scanning Electron Microscope Images (EPMA Systems)

As I resume my life in geologic research (more on that later), it seem appropriate to make my last entry on technical photography and wrap-up the Rock Photography Series.

Most of you have heard of and seen Scanning Electron Microscope Images (SEM), but maybe you never really thought of them as photography. Anything involving a camera is photography. In this case the ‘light’ for the exposure is actually electrons reflected off of the surface of the thin section sample and collected by a spectrometer. Magnification may be 10X to 1000X depending upon, in this case, the size of the mineral crystals.

An SEM is optimized for imaging, and has a less precise chemical analysis mode. When the same instrument is designed to optimize analytical capabilities it is called an Electron Probe Micro-Analyzer (EPMA). This is what I typically used, rather than an SEM. But it is still possible, and often highly desirable to take images of the samples. The standard film type was Polaroid 4X5. I guess the newer models will use digital imaging by now.

Tech Photos: SEM Electron Imaging

The white mineral is Spinel (Left a close-up with the scale bar representing 10 microns; Right the Spinel shown within the crystal matrix, scale bar 100 microns).

Minerals composed of heavier elements reflect the most electrons and are therefore brighter. Spinel is an Iron-Magnesium oxide. The Points marked on the image to the left are the points that I chose to analyze.

This is the mineral Zircon. Zircons have been used to date the oldest events in Earth History, because they are virtually indestructible once formed. Each layer that you see represents a new geological event in the 'life' of this Zircon. This mineral is a primary source for the element Zirconium and was mined fro a heavy mineral sand deposit.