EDS analysis of the Winchcombe meteorite

Introduction

Analysing meteorite samples in an SEM is always exciting but analysing a piece of rare carbonaceous chondrite meteorite, estimated to be around 4.6 billion years old, is incredibly good fun! It is like time travelling!

Recently, we had the privilege to analyse the Winchcombe meteorite that fell in the little Gloucestershire town in February 2021. The extra-terrestrial rock fell to earth in a spectacular fireball that was witnessed by over a thousand people in the UK. The UK Fireball Alliance (UKFAll) quickly responded to the event and, with the help of local residents in Winchcombe, recovered about 600g of meteoritic material in an excellent condition for scientific analysis. The fragments didn't experience rainfall prior to collection and were placed in a protected environment within 12 hours of the fall, meaning that the quality of the samples is similar to those retrieved from asteroids by space probes.

The largest part of the meteorite is now on display at the Natural History Museum in London. Other parts were shared with different laboratories across the UK for meticulous analysis with a range of techniques, forming the UK Winchcombe consortium study.

Scrutiny of the meteorite showed that it is a rare type known as a carbonaceous chondrite meteorite of similar age to the Earth itself, at just below 4.6 billion years. Understanding the microstructure and composition of this meteorite can give insights into how our planet formed and what the early solar system was like, which in turn can give important clues about the origins of the oceans and life on earth.

Oxford Instruments is part of the UK Winchcombe consortium study, and we received a sample of the meteorite from the Natural History Museum. This application note shows some preliminary results which highlight the magnificent microstructure of this meteorite.

Figure 1. Winchcombe meteorite displayed at the Natural History Museum of London. Photograph from Trustees of the Natural History Museum, London.

Results

For this analysis, a high resolution FEG-SEM equipped with an Ultim Max 170 EDS detector and AZtecLive software was used. In order to have a good overview of the sample, a large area map of the whole sample was collected, i.e. a series of simultaneous electron images and X-ray maps stitched to form one large map (Figure 2). It gave an initial overview of the chondrules and metal grains present.

Figure 2. A series of individual maps stitched together to form a Large Area Map of the meteorite sample using AZtecLive software. The red box is the area that is shown in detail in Figure 3.

Live Chemical Imaging (LCI) was used to great advantage to find areas of interest easily and quickly. With this new technology, it was possible to navigate and see the X-ray elemental maps live; a huge improvement in ease of use and throughput compared to the conventional "move, stop, collect and repeat" workflow.

A short video of the navigation of the sample using LCI can be seen here.

In the video, an area of particular interest was found located on the external top layer of the meteorite as seen in Figure 2, ranging from 0.5 µm to a few hundreds of microns in thickness. It clearly has a different structure to the rest of the sample. This surface layer is known as a fusion crust. A fusion crust is a thin melted layer created under high temperatures when the meteorite entered our atmosphere at very high speed (typically between 15 and 70 km/ seconds). Although it takes only 4 to 5 seconds for the meteorite to pass through the atmosphere, the event generates so much energy it melts the surface of the meteorite (hence the spectacular fireball seen by so many observers).

Figure 3 shows two high resolution maps of the fusion crust at different magnifications collected from the area highlighted with a red rectangle in the large area map (Figure 2). The analysis shows a fine-scaled microstructure with faceted iron oxide and olivine grains in a silicate-rich matrix. The core part of the meteorite has several fascinating microstructures, one of the most beautiful EDS maps is shown in Figure 4.

Figure 3. (a) EDS map combined with secondary electron image from the fusion crust layer of the Winchcombe meteorite at 1,000X magnification and (b) at 10,000X magnification.

Figure 4. Ultra-high resolution EDS map collected using Ultim Max 170. The map shows an Fe-rich serpentine vein structure occurring in an altered olivine grain.

Conclusion

This application note has given an insight into the fascinating microstructure of this meteorite. Please do keep an eye out for more information on our website and more application notes as our research on the Winchcombe meteorite progresses!