The study of fission track and other crystalline defects using confocal scanning laser microscopy

Confocal scanning laser microscopy (SLM) is a technique that offers geologists a new way of studying structures in minerals at the submicrometre level. As an example we show how the non-destructive nature of confocal SLM can be used to measure and count fission tracks (line defects formed by the spontaneous fission of²³⁸U) in the uranium-bearing mineral apatite, and to provide information about the geometry and crystallographic orientation of fluid inclusions trapped inside apatite grains during crystallization. The technique also provides a means of studying the internal geometry of chemical zonation in minerals. The digitized nature of the SLM images makes them amenable to a variety of image analysis techniques, and we show how image analysis can be used to measure fission tracks in mica sheets and provide crude estimates of track dip. Finally, using a chemically etched mica sheet we show how confocal SLM can be used to provide a detailed near-surface (1–5 μm) analysis of geological materials.