Mineral Identification with EDS Mapping

Aim

To differentiate minerals in a rock sample that have similar appearance in electron images.

Challenge

Rocks are typically heterogenous materials that contain a variety of different phases, each with their own properties. Traditionally, initial investigation of them is with either secondary electron (SE) or backscattered electron (BSE) imaging. BSE signals are often used to spot compositional variations across a sample due to the contrast mechanism in these images being related to average atomic number (Z). However, a problem arises when we need to differentiate mineral phases with similar mean Z numbers.

Solution

By using EDS mapping, it is easy to identify the different elements, and so minerals present in the sample — even grains with similar BSE intensity can be chemically distinguished. In order to do this accurately and avoid potential element mis-identifications, we need to take advantage of advanced algorithms which correct for a variety of common effects. This process can be run in either a static way or in a live implementation where maps are acquired in real time during navigation around a sample.

Results

The BSE image reveals different intensity grains (circled); the left one is brighter, the other two have similar BSE intensity. The resulting EDS overlayed maps and individual element maps can be used for mineral identification. This can also be done from spectra reconstructed post-acquisition.

Figure 1. The BSE image reveals different intensity grains (circled), the left one is brighter, the other two have similar BSE intensity. The resulting EDS overlayed maps and individual element maps can be used for mineral identification. This can also be done from spectra reconstructed post-acquisition.

Conclusion

The acquired hyperspectral EDS map data reveals the true mineral species via the element combinations seen in the EDS X-ray maps: Zircon ZrSiO₄ from the Zr map, Rutile TiO₂ from the Ti map, and Apatite Ca₅(PO₄)₃ from the Ca and P maps. The use of AZtecLive's TruMap functionality provides confidence in the results as it corrects for multiple effects which could otherwise cause misidentification of elements.