Backscattered Electron Imaging and Microanalysis of Iron-Titanium Oxide Minerals in Fine-Grained Igneous Rocks

Abstract

<jats:p>Oxides of iron, titanium, and iron &amp; titanium occur as accessory mineral components of most igneous rocks and generally comprise 1-2% of the total rock volume. In the fine-grained rocks the crystals are usually equidimensional and less than 1 mm across. Because most of them are opaque they cannot be examined using polarized transmitted light in the standard petrographic microscope and must be identified by reflected light (1). We have chosen to study these minerals in the SEM using BSE imaging and EDS microanalysis of carbon-coated polished sections of the rocks which contain them. Alhough this does not permit precise identification of the minerals the technique does reveal textural details which cannot be seen with light microscopy and also allows chemical analysis of the grains or parts of the grains. Furthermore, all these the oxide minerals are very easy to see in the BSE images because they are a higher atomic number (Z) than the silicates that form the bulk of the rock.</jats:p>