57Fe Mössbauer studies of meteorites

Program Code: 
1892
Contact: 

Prof Sean Cadogan (s.cadogan@adfa.edu.au)

Description of Work: 

Objectives:

The classification of meteorites usually involves three major categories which are distinguished on the basis of the amounts of metallic Fe-Ni and Fe-bearing silicates they contain. Irons are mainly Fe-Ni metal, Stones are mainly silicates with a small amount of metal and Stony Irons have roughly equal amounts of metal and silicates. Stony meteorites can be further subdivided into chondrites and achondrites. About 85% of observed meteorite falls are chondrites that most likely originated in asteroidlike objects which were never large enough to undergo melting in the early stages in the formation of the Solar System.

We have a set of meteorite samples that were collected in two hot desert regions: the Nullarbor Desert in Australia and the Sahara Desert in North Africa. Meteorites falling in such dry regions tend not to weather away too quickly.

In this project we will carry our 57Fe Mössbauer spectroscopy on a number of meteorites to identify the oxidation states and crystal chemistry of the Fe-bearing meteoritic phases. When a meteorite reaches Earth, all the iron is present as either Fe0 or Fe2+ Fe2+, with effectively no Fe3+. Therefore, any Fe3+ present in a recovered meteorite can only have been formed on Earth and reflects the interaction of the meteorite with the climatic conditions present at the crash-site. Such information is important to the study of terrestrial climate and involves question such as whether or not meteorites record a signal of the terrestrial climate at the time of their fall. This information can also be used to determine the ‘Terrestrial Age’ of the meteorite i.e. how long has the meteorite been on Earth. We will also study the nanoparticles of Fe-oxides and hydroxides present in a meteorite and investigate their magnetic behaviour at low temperatures.

Description of Work:

  • Preparation of meteorites for 57Fe Mössbauer Spectroscopy measurements;
  • Carry out basic measurements of a meteorite’s magnetic properties using acsusceptibility;
  • Obtain 57FeMössbauer spectra over the temperature range 4–300 K;
  • Analysis of the 57Fe Mössbauer spectra, identification and quantification of the Fe-bearing phases present in the meteorite;
  • Study the magnetic ordering of the nanoparticle Fe-oxides/hydroxides at low temperature.