The aim of qualitative analysis is to quickly identify the sample without resorting to detailed calibration and concentration measurement involced in quantitative analysis. The Energy Dispersive Spectrometer (EDS) in combination with a back-scattered electron (BSE) detector is ideally suited for this purpose. Electron back-scattering is a function of the average atomic number of the specimen. Hence, a BSE image efficiently distinguishes different phases in the sample (e.g., minerals in a rock) that cannot be distinguised easily in a conventional optical microscope image. For example, amphibole (amph) at the rim of clinopyroxene (cpx) cannot be easily recognized in the cross-polarized light image below:
Once phase distinctions based on electron back-scattering properties are made, the elements in each phase can be easily identified by collecting an EDS X-ray spectrum with the beam positioned on the phase. The EDS spectrum below shows a typical hornblende (a common amphibole mineral) spectrum. The clinopyroxene spectrum is similar but it does not show the potassium peak and aluminum is usually lower.