Guide 6 of 6

Telling iron oxides apart

Iron oxides and oxyhydroxides are among the most common minerals studied with Mössbauer spectroscopy. At room temperature many of them look alike, but their hyperfine fields and how they change on cooling set them apart.

Compare typical spectra

Choose a mineral and a temperature. The spectra are simulated from typical published values, listed in the table further down.

Typical values

Typical hyperfine parameters. δ is relative to α-Fe. For sextets the middle column is ε; for doublets it is ΔEQ.
Mineral Temperature Spectrum δ (mm/s) ΔEQ or ε (mm/s) Bhf (T)
HematiteRoom temperatureSextet0.37−0.1051.8
4.2 KSextet0.48+0.2054.2
GoethiteRoom temperatureSextet, often broad0.37−0.13about 38
4.2 KSextet0.48−0.1350.6
LepidocrociteRoom temperatureDoublet0.370.53—
4.2 KSextet0.470.0145.8
Ferrihydrite (2-line)Room temperatureDoublet0.35about 0.7—
4.2 KBroad sextet0.47about 0about 47
MagnetiteRoom temperature, A siteSextet0.26049.0
Room temperature, B siteSextet0.67046.0
MaghemiteRoom temperatureSextet0.320about 50

These are typical values for well-characterised samples. Real samples vary with crystallinity, particle size and substitution, so treat them as a guide rather than a rule. To see the published values for real samples, search the database, for example for hematite, goethite or ferrihydrite.

Tips for telling them apart

  • The isomer shift is not enough. All of these minerals are mainly Fe(III), with δ between about 0.3 and 0.5 mm/s at room temperature. The hyperfine field and its behaviour on cooling are more useful.
  • Hematite or goethite? At room temperature hematite's field (about 52 T) is much larger than goethite's (38 T or less). At 4.2 K their fields are closer, but hematite's ε is positive while goethite's stays negative.
  • Magnetite or maghemite? Magnetite has a second sextet with δ near 0.67 mm/s from the Fe(2.5+) site. Maghemite does not. Partly oxidised magnetite falls in between, and the ratio of the two sites shows how far it has oxidised.
  • A doublet at room temperature? It could be lepidocrocite, ferrihydrite or very small particles of goethite or hematite. Measure at 77 K and 4.2 K to tell them apart, as the guide on temperature explains.
  • Lower fields and broad lines often point to small particles or substitution, such as aluminium in goethite or hematite.

Further reading

  • Cornell, R. M. and Schwertmann, U. 2003. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses, 2nd edn. Wiley-VCH, Weinheim.
  • Murad, E. and Cashion, J. 2004. Mössbauer Spectroscopy of Environmental Materials and their Industrial Utilization. Kluwer Academic Publishers, Boston.
  • Thompson, A., Byrne, J. M., Dreher, C. L., Grigg, A. R. C., Joshi, P., Latta, D. E., Neumann, A., Notini, L., O’Neill, K. E. B. and Rothwell, K. A. 2025. Current practices for analyzing soils and sediments via Mössbauer spectroscopy. Journal of Plant Nutrition and Soil Science, 188, 742–773. doi:10.1002/jpln.12024